Dissertations / Theses on the topic 'Mangroves'

Ecotone entre les continents et l’océan, la mangrove couvre l’essentiel du littoral des régions intertropicales. Elle constitue un écosystème unique, façonné par un environnement très contraignant. Environnement à haute valeur scientifique et socio-économique, la mangrove subit cependant de multiples menaces. Le suivi de cet écosystème et la compréhension de sa dynamique constituent maintenant des priorités. Dans ce contexte, notre étude a d’abord porté sur l’amélioration de l’estimations des surfaces de mangrove au niveau mondial et sur le suivi de leur évolution, par l’utilisation de la télédétection. L’importance du proche infrarouge dans l’identification des mangroves a été alors mis en évidence. Nous nous sommes ensuite focalisés sur une région à forte activité hydro-sédimentaire : les mangroves des côtes subissant l’influence du fleuve Amazone. De l’individu au peuplement, du suivi de terrain à l’analyse des données de télédétection, nous avons alors caractérisé la dynamique de ces mangroves au travers de deux de ces phases essentielles. - Le développement d’un peuplement après la colonisation de nouveaux espaces (exemple des bancs de vase en Guyane française) : Le rôle de la microtopographie pour l’implantation des plantules, les phénomènes de croissance et la phénologie des jeunes individus ont été précisés. - La régénération de la mangrove adulte (exemple des chablis au Brésil) : La répartition des plantules à l’intérieur des chablis et l’importance là encore de la microtopographie ont été observées. Les possibilités de cartographie des chablis par télédétection ont été explorées. Des relations étroites entre cycles sédimentologiques et cycles biologiques ont ainsi été mis en évidence. Notre exploitation de données de télédétection variées, de l’optique à basse résolution au laser, participe à une meilleure utilisation de ces techniques pour l’étude et le suivi des écosystèmes de mangrove
Land-Ocean ecotone, the mangrove covers almost all the tropical littoral. It constitutes a unique ecosystem, built by a very constraining environment. Environment with high scientific and socio-economic value, the mangrove undergoes however multiple threats. The monitoring of this ecosystem and the comprehension of it dynamic contitute priorities now. In this context, our study focuses first on the improvement of the mangrove surfaces estimates at world level and on the monitoring of their evolution, by tremote sensing. The importance of the near infra-red for the mangroves identification was then highlighted. We then specially study an area of high hydro-sedimentary dynamic: mangroves under the Amazon river influence. From the individual to the settlement, from ground monitoring to remote sensing data analysis, we then characterized the dynamic of these mangroves through two key-phases: - The settlement growth after colonization of a new environment (example of the mud banks in French uiana): The role of microtopography for the seedlings establishment, the growth phenomena and the phenology of the young individuals were specified. - The regeneration of the adult mangrove (example of forest gap in Brazil): The distribution of the seedlings inside gaps and the importance there still of microtopography were observed. The possibilities of gap cartography by remote sensing were explored. Close connections between sedimentological cycles and biological cycles were thus highlighted. Our use of varied remote sensing data, from optical low resolution to Lidar, takes part in a better use of these technics for the study and the monitoring of the mangrove ecosystems

Mangrove ecosystems thrive in (sub)tropical, intertidal areas where adaptations

like vivipary and the hydrochorous dispersal of propagules become an absolute

necessity. As propagule dispersal and early growth allow for the replenishment of

existing stands and colonization of new habitats, many authors recognize the

importance of these stages in structuring mangrove populations and communities.

However, when it comes to the actual propagule dispersal and recruitment

mechanisms, there is an apparent lacuna in the current understanding of

mangrove ecology. The period between the mature propagule falling from the

parental mangrove tree and the early growth of the established seedling, under

various possible circumstances, remains in the dark. In this study we focus on this

particular period by investigating both the places where these propagules end up

as the pathways their dispersal units follow. And we go one step further.

Mangrove forests are being destroyed worldwide at a threatening pace despite

their tremendous asset to coastal human communities and associated biological

species. The effect of human-induced (cutting and mangrove conversion to

aquaculture ponds) as well as indirectly and/or ‘naturally’ evolving disturbances

(sea level rise) on propagule hydrochory occupies an important place in this study.

Dispersal of water-buoyant propagules of the family Rhizophoraceae and

Acanthaceae (now including the Avicenniaceae) was studied in Gazi Bay (Kenya),

Galle and the Pambala-Chilaw Lagoon Complex (Sri Lanka). The study sites

differ both in tidal regime and vegetation structure, covering an interesting variety

of ecological settings to examine propagule dispersal. Field data and experiments

ranging from micro/ mesotopographical measurements and successive propagule

counts to hydrodynamic and propagule dispersal experiments were collected or

executed in situ.

Two main methodological approaches were employed. Firstly, the question on

mechanisms of propagule recruitment was addressed by statistically investigating

the effect of microtopography, top soil texture and above-ground-root complexes on

the stranding and self-planting of propagules (Chapter 2&3). Afterwards,

suitability maps were created using Geographical Information Systems (GIS) to

assess whether a particular mangrove stand has the ability to succesfully

rejuvenate. Furthermore, the effect of degradation (tree cutting) (Chapter 2&3),

sea level rise (Chapter 2&4) and microtopography-altering burrowing activities of

the mangrove mud lobster Thalassina anomala (Chapter 3), was incoporated in the

GIS-analyses. Secondly, the combined set-up of hydrodynamic modelling and

ecological dispersal modelling was developed to simulate propagule dispersal

pathways influenced by dispersal vectors (tidal flow, fresh water discharge, wind),

trapping agents (retention by vegetation or aerial root complexes) and seed

characteristics (buoyancy, obligated dispersal period) (Chapter 5&6). This type of

approach provided the possibility to explore propagule dispersal within its

ecological context, but was also applied to an implication of shrimp pond area

restoration (Pambala-Chilaw Lagoon Complex, Sri Lanka) (Chapter 5) and to

evaluate changes in propagule dispersal when sea level rises (Gazi Bay, Kenya)

(Chapter 6).

The main findings regarding propagule recruitment indicate that propagules are

not distributed equally or randomly within a mangrove stand, yet species-specific

distribution for anchorage occurs. Characteristics of the environment

(microtopography, top soil texture and above-ground root complex) influence

propagule recruitment in a way that complex root systems (e.g. pencil roots and

prop roots) facilitate the entanglement of dispersal units and a more compact soil

texture (like clay and silt) and a predominant flat topography creates suitable

areas for stranding and self-planting of propagules. This combines effects of

existing vegetation and abiotic factors on mangrove propagule establishment.

Since propagule dispersal is not solely determined by species-specific propagule

characteristics (e.g. buoyancy, longevity, etc.), I emphasize that propagule sorting

by hydrochory has to be viewed within its ecological context. Propagule retention

by vegetation and wind as a dispersal vector, deserve a prominent role in studies

on propagule dispersal. The significance of dense vegetation obstructing long

distance dispersal (LDD in its definition of this work), mainly in inner mangrove

zones, supports our main finding that propagule dispersal is largely a short

distance phenomenon. ‘Largely’ is here understood as quantitatively, not

excluding epic colonization events of rare but important nature.

In accordance with the Tidal Sorting Hypothesis (TSH) of Rabinowitz (1978a),

smaller, oval-shaped propagules were found to disperse over larger distances than

bigger, torpedo-shaped propagules. We can however not fully support the TSH

because (1) these differences are no longer valid when comparing between torpedoshaped

propagules of different sizes and (2) propagule dispersal is not always

directed towards areas more inland, but can be strongly concentrated towards the

edges of lagoons and channels

Anthropogenic pressure on mangrove ecosystems, more specifically clear-felling or

mangrove conversion to aquaculture ponds, imposes limitations on propagule

recruitment due to reduced propagule availability and a decrease in suitable

stranding areas where the architecture of certain root complexes, like prop roots

and pencil roots, function as propagule traps. These types of pressure appear to

have more severe consequences on propagule dispersal than the effect of sea level

rise on mangroves. Mangrove forests, which are not situated in an obviously

vulnerable setting, can be resilient to a relative rise in sea level if a landward shift

of vegetation assemblages and successful early colonization is not obstructed by

human-induced pressures. Also, and this renders mangrove forests vulnerable in

spite of their intrinsic resilience, when the ‘capital’ of forest is severely reduced or

impoverished as happens extensively worldwide, the ‘interest’ on this capital,

understood as propagule availability, delivery and trapping, will not allow them to

efficiently cope with sea level rise, putting sustainability of mangrove ecosystem

services and goods at risk.

In a larger framework of mangrove vegetation dynamics, knowledge on propagule

dispersal will benefit management strategies for the conservation of mangroves

worldwide, besides its fundamental interest to fully fathom the ecology of this

particular marine-terrestrial ecotone formation.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

In South Africa mangrove forests are located in estuaries from Kosi Bay in KwaZulu-Natal (KZN) to Nahoon Estuary in the Eastern Cape. The aims of this study were to determine the present state of mangroves in KwaZulu-Natal, by assessing the current population structure, the changes in cover over time and associated anthropogenic pressures. A second objective of this study was to determine the effect of harvesting on the population structure and sediment characteristics in the Mngazana mangrove forest. To determine if harvesting was sustainable at Mngazana Estuary; the growth and mortality rates and associated growth conditions were measured. Finally by using population modelling sustainable harvesting limits were determined by predicting the change in population structure over time. The study focussed on the KwaZulu-Natal province as a fairly recent study addressed mangrove distribution and status in the Eastern Cape Province. A historical assessment of all mangroves forests in KwaZulu-Natal (KZN) revealed that the potential threats to mangroves in South Africa include; wood harvesting, altered water flow patterns coupled with salinity changes, prolonged closed-mouth conditions and subsequent changes to the intertidal habitat. As a result mangroves were completely lost from eleven estuaries in KZN between 1982 and 1999 and a further two estuaries by 2006. Mangroves only occurred in those estuaries where the mouth was open for more than 56 percent of the time with the exception of St Lucia, where the mouth has been closed for longer but the mangrove communities have persisted because the roots of the trees were not submerged. All mangrove forests in KZN were regenerating in terms of population structure as they had reverse J-shaped population curves as well as high adult: seedling ratios. Kosi Bay and Mhlathuze Estuary were two of the larger forests that showed signs of harvesting (presence of tree or branch stumps), but the greatest threat to smaller estuaries seems to be altered water flow patterns due to freshwater abstraction in the catchments and the change of land use from natural vegetation to sugar-cane plantations. These threats affect the hydrology of estuaries and the sediment characteristics (particle size, redox, pH, salinity, temperature) of the mangrove forests. The environmental conditions under which the mangrove forests currently exist were determined for five species. Lumnitzera racemosa and Ceriops tagal exhibited a narrow range of conditions as these species are only found at Kosi Bay, while Avicennia marina, Bruguiera gymnorrhiza and Rhizophora mucronata were found to exist under a wider range of conditions. The growth rate and response to environmental conditions of the three dominant species were important to determine as these species are impacted by harvesting. Mangrove growth rates were measured at Mngazana Estuary in the Eastern Cape, the third largest mangrove forest in South Africa. Areas of this estuary where mangroves harvesting has occurred, show significant differences in sediment characteristics as well as changes in population structure in harvested compared to non harvested sites. The growth rate (in terms of height) of Avicennia marina individuals increased from seedlings (0.31 cm month-1) to adults (1.2 cm month-1), while the growth of Bruguiera gymnorrhiza stabilised from a height of 150 cm at 0.65 cm month-1. The growth of Rhizophora mucronata peaked at 0.72 cm month-1 (height 151-250 cm) and then decreased to 0.4 cm month-1 for taller individuals. Increases in diameter at breast height (DBH) ranged between 0.7 and 2.3 mm month-1 for all species. Some environmental variables were found to be important drivers of growth and mortality of individuals less then 150 cm. A decrease in sediment pH significantly increased the mortality of Avicennia marina seedlings (0-50 cm) (r = - 0.71, p<0.05) and significantly decreased the growth of Rhizophora mucronata and Bruguiera gymnorrhiza seedlings (r = -0.8, r = 0.52 – p < 0.05 respectively). At Mngazana Estuary, mortality of this species showed a positive correlation with sediment moisture content indicating that this species prefers drier conditions. The density of Rhizophora mucronata was significantly correlated to porewater temperature in Northern KZN as was the growth of adult (>300 cm) Rhizophora trees at Mngazana Estuary. Mortality of Avicennia marina individuals (51-150 cm) was related to tree density indicating intraspecific competition and self thinning. Selective harvesting of particular size classes of Rhizophora mucronata was recorded when comparing length of harvested poles (~301 cm) and the size class distribution of individuals. Taking into account the differences in growth rate for each size class for this species it will take approximately 13 years to attain a height of 390 cm which is the height at which trees are selected for harvesting at this estuary. This is 2.6 times slower than those individuals growing in Kenya. The feasibility of harvesting is dependent on the growth rate of younger size classes to replace harvested trees as well as the rate of natural recruitment feeding into the population. Different harvesting intensity scenarios tested within a matrix model framework showed that limits should be set at 5 percent trees ha-1 year-1 to maintain seedling density at > 5 000 ha-1 for R. mucronata. However harvesting of Bruguiera gymnorrhiza should be stopped due to the low density of this species at Mngazana Estuary. Harvesting of the tallest trees of Avicennia marina can be maintained at levels less than 10 percent ha-1 year-1. Effective management of mangrove forests in South African is important to maintain the current state, function and diversity of these ecosystems. Management recommendations should begin with determining the freshwater requirements of the estuaries to maintain the mouth dynamics and biotic communities and deter the harvesting of (whole) adult trees particularly those species that do not coppice. Further management is needed to ensure that forests are cleared of pollutants (plastic and industrial), and any further developments near the mangroves should be minimized.

Mangrove communities are vulnerable to oil spills due to their location close to harbours, onshore and offshore oil production facilities, oil exploration facilities and tanker routes. Many oil spill accidents have been reported and the literature on these accidents has been examined with particular emphasis on the effects of oil on mangroves and other organisms. Most of the published studies have resulted from research after oil spill accidents occurred. However, there are very few detail studies on oil dose-response (plant symptomatology, growth, physical and chemical action) relationships in plants and sediments. An understanding of the effects of oil on mangroves may assist in predicting the interactions between oil exposure factors, species sensitivity and environmental factors. The study was designed to determine the concentrations, the time dependencies, and the lethal and subtle effects of spilled oils on different ages of mangroves, with particular focus on mangrove seedlings. The effects of volatile hydrocarbons and the interactions of oil with anoxia (lack of oxygen) on plants and sediments were also studied. Moreover, the aims of the experiments were to characterise the toxic fractions by recording chemical action of two oil types on plant leaves and sediments. The results were expected to determine the resistant index of mangroves to oil spills (time and dose) and to clarify the chemical compounds and concentrations which were toxic to mangroves. Kuwait Crude Oil (KCO) and North West Shelf Condensate (NWSC) were chosen for use as common heavy and light grade oils, respectively. Different age levels (seeds, seedlings and saplings) of Avicennia marina, Ceriops tagal, Rhizophora stylosa and Rhizophora mncronata were chosen for experiments due to their differences in morphological features, physiological processes and sizes. The research was divided into two main exposure conditions, laboratory and field conditions. Each species was exposed to different selected doses of oil, ranging from very low (27.5 g m-2) to very high (1100 g m-2), applied to the sediment surface only, or to the sediment surface and shoots. Very low (27.5 g m-2), low (275 g m-2) and medium (1375 g m-2) doses of KCO did not permanently affect the total metabolic processes for plant survival. In certain case, these doses stimulated growth. However, application of the same doses of NWSC produced chronic effects. Exposure to higher doses (2750, 5500 and 11000 g m-2) of both oils significantly increased injury symptoms and decreased plant growth. The interactive effects between oil treatment and duration of treatment were mostly antagonistic at medium high and high doses of oil and became synergistics at very high doses of oil. Application of oil to the sediment and shoots had more acute impacts than application to the sediment surface only, as indicated by a higher symptom index, leaf abscission and mortality, decreased plant growth and reduced biomass. There were variable effects on leaf area and biomass accumulation as responses of any species were affected more by individual plant-size than by oil treatments. The greater tolerance of biomass responses to oil treatments may be because of its slower response to the stress as it follows physiological and biological changes. In certain cases, the effects were more complicated due interactions of response to oil with other environmental stresses. Although the effects of NWSC and KCO on mangroves were variable, A. marina was more sensitive to both types of oil than the three other species. The differences in morphological features and physiological processes may play an important role in sensitivities of different species. Plant stress in Avicennia mangroves was exhibited as primary effects in response to the toxicity of high concentrations of hydrocarbons and other toxic fractions in plant tissues; while, the stress in Rhizophora mangroves was caused by secondary effects such as physical and chemical changes in sediments which affected nutrient deficiencies and metabolic disruptions. Dose-response relationships for individual oil types were different in each species, and were variable under different conditions of experiment. Different species origin, culturing system, sediment characteristics and environmental factors may cause different sensitivities. Furthermore, differences in the capacity of metabolism, and different ages of mangroves resulted in different sensitivities when the same type and doses of oil were applied. The most sensitive age was seed germination, followed by seedlings and saplings, respectively. NWSC as a light oil was more toxic than KCO (a heavy oil) in all species and all age levels of mangroves. The chemical compositions of hydrocarbons in plants was more important than concentration in producing lethal and sublethal impacts than in KCO. The higher increased content of aromatic fractions in NWSC may confer the considerably degree of toxicity to plants. However, different doses of oil caused different responses in each species. While both oils were greatly degraded with time under laboratory and field conditions, the degradation of NWSC was faster than KCO in sediments. The degradation processes may also be influenced by rainfall, tidal flushing, weathering processes (evaporation), biological factors (bacteria, fungi and other micro-organisms) and environmental factors (temperature, oxygen, nutrients, salinity and pressure). In conclusion, different types and doses of oil, and duration of exposures produced different responses in each species of mangroves. Depending on amount of oil applied, the responses developed from growth stimulation to chronic and acute impacts. However, the mechanism of damage appeared to be similar in all species. The responses included foliar injury (leaf chlorosis and necrosis), leaf abscission, stem deformation, reduced number of new leaves, reduced plant growth and biomass accumulation, and mortality.

The saltwater mosquito, Aedes vigilax (Skuse), is a major vector of Ross River virus and Barmah Forest virus across sub-tropical and tropical Australia, and poses a significant human health risk, particularly in densely populated areas such as South East Queensland and Northern New South Wales regions of eastern Australia. The insect uses saltmarsh and mangrove basin forests as oviposition and larval habitats, and various mosquito control methods exist that target larval stages. Fish, acting as predators of larvae, have routinely been used as a component of mosquito control strategies worldwide. If managed appropriately biological control using fish can be effective, but if mismanaged, biological control can have serious environmental consequences. For example, the release of the Mosquitofish (Gambusia holbrooki (Girard)) for mosquito control in Australian waterways has caused significant ecological damage; G. holbrooki is now a major invasive pest. Nonetheless, mosquito control strategies that include the use of native fish populations in the strategy may be more effective for controlling mosquitoes in mangrove basins than those that do not include native fish. However, little is known of fish populations (both exotic and native) within mangrove basins, and the impact these fish do, and could have on mosquito populations. This research examines the relationship between resident fish and saltwater mosquitoes in eastern Australian mangrove basin forests. It focussed specifically on two mangrove basin sites in the South East Queensland/Northern New South Wales region, and evaluates the potential of resident mangrove basin fish as biological control agents in mangrove ecosystems.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

Cette etude s'integre a celles qui concernent le fonctionnement des ecosystemes mangrove et notamment les relations entre les differents peuplements et les principaux parametres de leur environnement (regime hydrique, cycle des nutriments, stabilite du substrat). La biosystematique du genre avicennia, un des principaux composants des mangroves, est indispensable a de telles etudes. Les differents auteurs ne s'accordant pas sur le nombre d'especes d'avicennia (ils en ont decrit jusqu'a 20), une des premieres difficultes est de determiner ce nombre. Cette etude biosystematique se base sur une des classifications les plus recentes qui decrit 8 especes dont 3 dans la region afrique de l'ouest/amerique (a. Germinans, a. Schaueriana et a. Bicolor) et 5 dans la region indo-pacifique (a. Alba, a. Rumphiana, a. Officinalis, a. Integra et a. Marina). Cette etude consiste en une revision des caracteres morphologiques et une recherche de nouveaux marqueurs taxonomiques en anatomie (hypoderme, nervure mediane, idioblastes), phytodermologie (stomates, glandes a sel, trichome) et phytochimie (iridoides). L'anatomie a permis de discriminer 2 groupes au sein du genre avicennia en fonction des differents types de poils (definis sur le nombre de cellules-socle) et des differences tissulaires de la nervure mediane (anneau de sclerenchyme, faisceau abaxial, presence d'idioblastes autour de la nervure). L'isolement de 2 iridoides a partir d'a. Germinans puis leur dosage dans chaque espece grace a des techniques chromatographiques, ont apporte de nouvelles informations au niveau infraspecifique, en particulier pour les populations americaines et africaines d'a. Germinans. L'analyse cladistique des differents caracteres permet une reconstitution phylogenique des avicennias qui tend a confirmer leur origine asiatique et leur migration d'une part vers l'afrique de l'est (a. Marina), d'autre part vers le continent americain (a. Bicolor, a. Schaueriana et a. Germinans), puis vers l'afrique de l'ouest (a. Germinans).

Les mangroves sont considérées comme des filtres efficaces entre la terre et la mer, étant des puits pour les métaux traces et protégeant les eaux côtières des pollutions. Cependant, cette capacité peut dépendre des caractéristiques des sols de mangrove et de l’hydrologie. Le devenir des éléments traces métalliques dans les mangroves est complexe en raison de divers processus biogéochimiques qui s’y déroulent. En raison de leur toxicité pour la biodiversité des mangroves et pour la santé humaine, le cycle des métaux traces est une question sérieuse abordée par de nombreux scientifiques au cours des dernières décennies et de nos jours. Contrairement au reste du monde, la distribution des métaux traces dans la mangrove du Viet Nam a reçu peu d’attention. L’objectif de cette thèse était de caractériser la dynamique des métaux traces dans la mangrove de Can Gio, située au sud du Vietnam, à la limite d’une mégapole densément peuplée – Hô Chi Minh-Ville (près de 10 millions d’habitants) et de la mer de Chine méridionale. Le long de l’estuaire du Can Gio, les métaux traces, principalement issus des sols latéritiques se développant en amont, ont été principalement transportés avec des matières en suspension, notamment des oxihydroxydes. Après avoir été déposés dans les mangroves, les oxihydroxydes sont dissous par des bactéries au cours des processus de décomposition de la matière organique en conditions suboxiques, libérant des métaux traces dans les eaux interstitielles. L’enrichissement des sols de mangrove en matière organique joue un rôle clé dans les processus diagénétiques. Les métaux dissous peuvent reprécipiter avec de nouvelles phases porteuses telles que des complexes organométalliques, des sulfures, des carbonates, etc., en fonction des conditions redox du sol et des caractéristiques de l’élément. De plus, une partie de ces métaux dissous est biodisponible et peut être transférée vers la végétation ou la faune des mangroves, une partie peut également être exportée vers les creeks. Par conséquent, cette thèse a démontré que les écosystèmes de mangrove peuvent être des sources de métaux traces pour les écosystèmes adjacents
Mangroves are considered as efficient barriers between land and sea, being sinks for trace metals and protecting coastal water from pollutions. However this ability may depend on sediment characteristics and hydrology. The fate of trace metal is complex due to various biogeochemical processes across the intertidal zone. Because of their toxicity to mangrove biodiversity and also to human health, the trace metal cycling is a serious question addressed by many scientists during the last few decades and nowadays. In contrast to the rest of the world, trace metal distribution in Viet Nam’s mangrove forest has received little attention. The aim of this research was to characterize some trace metals dynamics in the Can Gio mangrove, which is located in the Southern Viet Nam, being situated at the edge of a densely populated megacity – Ho Chi Minh City (i.e. almost 10 million inhabitants) and the South China Sea. Along the Can Gio estuary, trace metals, which mainly originated from upstream lateritic soils, were transported mostly associated with suspended solids, mainly oxihydroxides forms. After being deposited in mangrove sediments, the oxihydroxides were dissolved by bacteria during organic matter decay processes under suboxic condition, releasing trace metals in pore-waters. The enrichment of mangrove derived-OM from the mudflat to the Rhizophora stand played a key role in controlling diagenetic processes. Dissolved metals were then reprecipitated with new bearing phases such as organometallic complexes, suphides, carbonate etc. depending on the redox condition and on metal characteristics. Furthermore, part of these dissolved metals were available for biota uptake or export to tidal creek by pore-water seepage. Consequently, this PhD thesis also demonstrated that mangrove ecosystems can be sources of trace metals for adjacent ecosystems

This dissertation explores the hydrologic controls on salinity within mangroves and lagoons at sites in Florida and Mexico. The main objective of this research is to better understand hydrologic controls on mangrove ecosystem structure and develop ideas that will be useful to land managers attempting to regulate and conserve these critical habitats. This study was conducted at sites in Ft. Pierce, FL and Costalegre on the central Pacific coast of Mexico. We examined controls on water levels and salinity in a mangrove on a carbonate barrier island along the Indian River Lagoon, east-central Florida. Spectral analysis of water levels showed that mangrove groundwater levels are not tidally influenced. Salinities vary spatially, with values of ~10 in upland environments to ~75 psu in irregularly-flushed mangroves. Water chemistry indicates that water salinities are largely controlled by enrichment due to evapotranspiration. An electrical resistivity survey showed that the freshwater lens is restricted to uplands and that hypersaline waters extend deeply below the mangrove. These results indicate that evapotranspiration lowers water levels in the mangrove, which causes Indian River Lagoon water to flow into the mangrove where it evapoconcentrates and descends, forming a thick layer of high-salinity water below the mangrove. Spatial variability of terrain conductivity in the Ft. Pierce mangrove varied under two hydrologic management regimes, breached rotational impoundment management and rotational impoundment management. The difference in coefficient of variation (CV) between the breached RIM and RIM data was calculated to examine spatial variability in both the shallow and deep layers. A null-hypothesis model was employed to examine the statistical significance of the CV results. The average water levels were -0.06 m amsl and 0.49 m amsl during the breached-RIM and RIM regimes, respectively. The average shallow (EM31) layer terrain conductivity shifted slightly from 1868 mS m -1 to 1825 mS m-1 after the alteration in management regime, yet the standard deviation of these averages decrease from 656 mS m-1 to 216 mS m-1. The average deep (EM34) layer terrain conductivities were 328 mS m-1 and 255 mS m-1 during the breached-RIM and RIM regimes, respectively. The temporal CVs were 0.23 and -0.04 for the shallow and deep layers, respectively. The null-hypothesis model for the shallow layer illustrates that the difference in spatial structure is statistically significant. The deep layer CV was not statistically significant. These results indicate that the transition from breached RIM to RIM resulted in changes to both the physical and chemical hydrologic character of the impoundment, especially in the shallow layer. The second study sites were three mangrove communities along the central Pacific Mexican coast. Salinities varied by water type, with values of ~9 in La Manzanilla, ~17 in La Vena, ~33 in Barra de Navidad, ~0.4 in the fresh waters, and ~34 in the seawater. Sodium and Chloride concentrations and isotopic signatures, as well as salinity, were used as tracers in mass-balance mixing models to quantify estimates of relative fresh-water and seawater contributions to each site. La Manzanilla, a basin mangrove, had mean fresh-water contribution estimates of 63-84%. La Vena, a riverine mangrove, had fresh-water estimates of 39-51%. Barra de Navidad, a fringe mangrove, had low fresh-water contributions of 0-5%. These results illustrates that the role groundwater plays in mangrove hydrodynamics is dependent on the site hydrogeomorphology.

A partir d'une typologie physionomique standardisée, cette thèse entend proposer une méthode de cartographie des mangroves de l'Outre-mer français. Plusieurs jeux de données satellites sont ainsi exploités en vue (i) de déterminer l'extension des surfaces de mangroves, (ii) quantifier la fermeture de canopée, (iii) quantifier la hauteur de la canopée et (iv) identifier les principales espèces de palétuvier. La détermination des surfaces de mangroves se fait via l'exploitation des particularités spectrales des palétuviers dans le moyen-infrarouge visibles sur les images Landsat et Sentinel-2. La quantification de la fermeture de canopée est basée sur un algorithme doublement contraint (FCLSU) de démélengeage linéaire des pixels d'images très haute résolution Pléiades. La quantification de la hauteur de canopée a été effectuée quant à elle grâce à l'utilisation d'une analyse photogrammétrique d'un couple d'images panchromatiques stéréoscopiques WorldView-3 (0.3 mètres de résolution). Enfin, la discrimination des principales espèces de mangroves a été permise grâce à l'exploitation de relevés spectraux effectués sur le terrain et calibration des propriétés spectrales des différentes espèces visibles sur les images satellites
Based on a standardized typology, this thesis aims to propose a method for mapping the French Overseas mangroves. Several sets of satellite data are used to (i) determine mangrove extent, (ii) quantify canopy closure, (iii) quantify canopy height, and (iv) identify main species. Determination of mangrove extent was possible by using spectral characteristics of mangroves in the short wave infrared wavelength observed on the Landsat and Sentinel-2 images. Quantification of canopy closure is based on a fully constrained algorithm (FCLSU) of linear spectral mixture analysis of pixels of a very high resolution Pléiades images. Quantification of canopy height was performed using photogrammetric analysis of WorldView-3 stereoscopic panchromatic images (0.3 meters resolution). Finally, discrimination of main mangrove species was permitted through the use of spectral surveys and calibration of spectral properties of the different species observed on the satellite images

Acknowledging the increasingly prominent urban character of ecosystems globally, mangroves being no exception, and possible impediments to the viability of these ecosystems (i.e. the inherent capacity or ability to grow, develop or recover after disturbances), we adapt a system‟s approach to establish the viability of the peri-urban mangrove of Tudor creek in Mombasa, Kenya. Three important aspects of the peri-urban mangroves are assessed. These include (i) structural aspects (vegetation structure and regeneration), (ii) functional aspects (productivity) and (iii) human aspects (socioeconomics). Chapter 1 and 2 introduce the study, outlining the objectives and the study area. The chapters lay down an overview of the mangrove trees physiological adaptations and the ecological attributes that make the mangrove ecosystems unique and highly adaptable to a harsh and dynamic intertidal environment. The chapters further outline the extent and status of mangroves in Kenya, their socioeconomic importance, and the legislation that governs their management and conservation.

Chapters 3 and 6 describe the structural attributes and regeneration status of the peri-urban mangroves of Tudor creek. Based on species importance values the dominant mangrove species were Rhizophora mucronata Lam. (Rhizophoraceae) and Avicennia marina (Forssk.) Vierh. (Acanthaceae)&61607; Lumnitzera racemosa Willd. (Combretaceae), reported in an earlier floristic survey, was not encountered. Tree density varied between 1,264 trees ha–1 and 1,301 trees ha–1, which are within the range of values reported for similar forests globally. However, the size-class structure showed the numerical dominance of small trees over larger trees. The spatial distribution pattern of adults and juveniles varied greatly between sites had a close to uniform pattern (Morisita‟s Index Iδ << 1) for adult trees, but a tendency for clustered distribution (Iδ >> 1) for juveniles. This pattern of distribution is not expected for a healthy forest. The distribution of regenerating seedlings was mainly impacted by canopy gap sizes. These chapters shows that unmanaged but exploited peri-urban mangroves are structurally degraded, having enlarged canopy gaps, characterised by spatial and temporal heterogeneity in edaphic conditions that influences regeneration. This enlarged gaps and edaphic heterogeneity imposes longer periods for canopy closure by lowering regeneration and promoting mortality of seedlings. Larger gaps (> 60m²) had lower regeneration levels and intermediate gaps (20-50m²) had adequate regeneration. The occurrence of R. mucronata seedlings and saplings in the understorey under all cover types and inundation confers advantages to this species under the current disturbance regime. Disturbances include sewage pollution, unregulated harvesting and siltation. The current status of the forest is reminiscent of a recovery phase, a multiphase species succession stage, after a major disturbance event, accompanied by recurrent anthropogenic pressure. This study shows that species composition and thus recovery of a mangrove forest after disturbance depends in part on the balance between subsequent large-scale natural and recurrent small-scale human disturbances.

Chapter 4 assesses the human dependence on the peri-urban mangrove. Through questionnaires and field surveys, the study demonstrates the challenges of questionnaire surveys targeting respondents involved in exploitation of sensitive resources. This potentially limits if not inhibit information flow. Firewood is the ubiquitous form of mangrove wood utilisation, exploited at both subsistence and commercial scales. Forest assessments indicate the lack of preferred or specific harvesting sites, with R. mucronata being the most harvested, probably due to its distribution range and ease of access. Sewage pollution was viewed with mixed feelings. Many appreciate the nutrient enrichment of the sewage rather than the filtration capacity of mangroves, resulting in the usage of sewage for irrigating small plots of subsistence farms. The study shows that resource exploitation is intense in an urban setting due to an economic drive and an increasing demand. In the rural setting on the other hand, utilisation included both subsistence and commercial charcoal production. This has promoted more efficient, destructive and unsustainable exploitation levels. Associated benefits of these activities grossly under-value the ecosystem goods and services in addition to degrading the ecosystem. Our observations, consistent with other studies, shows that management of mangroves for wood extraction in urban areas may not be a viable and/or sustainable option, as it conflicts with the essential „filtration‟ and „habitat provisioning‟ functions and services of mangrove ecosystems. These functions and services are increasingly important in a “diminishing” urban environment. This arises out of the lack of adequate alternatives and conflicting interests in growing urban areas. It is recommended that „adaptive‟ and „participatory management’ based on multiple uses and users, with specific legislative, education and institutional interventions. Integrating local ecological knowledge, may further expedite the formulation of sustainable management plans for peri-urban mangroves. Chapter 5 presents insights on the productivity of an under-valued, over-exploited and sewage polluted peri-urban mangrove through litter fall studies on three common mangrove species, R. mucronata, A. marina and S. alba. The study covers a period of two years. The mean annual litter fall was estimated at 12 ± 3 t ha-1yr-1 for the whole stand, which is within the range of values reported for similar forests occupying the same latitudinal range. Litter fall, in both content and quantity was highly seasonal, with high rates occurring in the dry North Easterly Monsoon (NEM) season, January-April (ca. 5 ± 1 g DW m-2 day-1) and lower rates in the cool and wet South Easterly Monsoon (SEM) season, June-October (ca. 3 ± 0.5 g DW m-2 day-1). R. mucronata recorded the highest annual rate of 15 ± 3 t ha-1yr-1. No significant differences in litter fall rates were observed between A. marina and S. alba, (11 ± 3 and 10 ± 5 t ha-1yr-1 respectively). Sewage exposure levels did not appear to influence litter production rates despite higher nutrient levels in completely exposed sites. δ15N varied with species; A. marina (6.48 ± 0.03‰) and S. alba (6.76 ± 0.24‰) having higher composition than R. mucronata (3.88 ± 0.64‰). The leaf C:N ratio strongly correlated with elevated leaf δ15N signature. Higher C:N ratio for R. mucronata corresponding with lower leaf δ15N (3.88 ± 0.64‰) signature, and lower C:N ratio for A. marina and S. alba (6.48 ± 0.03‰ and 6.76 ± 0.24‰ respectively) corresponding with higher δ15N signature. This reflects species specific response to raw sewage exposure. This implies the forest has a more open N cycle, favouring δ15N accumulation within the system. This study shows that sewage exposure does not necessarily translate into elevated productivity in mangroves, but may alter litter nitrate content depending on species, possibly altering the decay of litter and nutrient cycling.

Chapter 7 presents a synthesis linking the findings to possible implications on the general status of the mangrove ecosystem. The major disturbances observed for the peri-urban mangroves of Tudor creek include (i) domestic sewage pollution, (ii) recurrent unregulated harvesting; and (iii) recurrent annual siltation during the rainy season. Our observations indicate that

(i) Raw domestic sewage pollution may not be harmful to the mangrove vegetation, but may affect edaphic conditions through nutrients enrichment. Sewage pollution effects, though not qualitatively proven in our study, enhance growth of mangrove trees. This is due to increase in amounts of nutrients available for biomass formation, observed as leaf nitrates resorption efficiencies. However, the raw domestic sewage is reported to alter the general healthy decomposing aerobic-anaerobic mangrove system to a complete anaerobic system. This tends to lower efficiencies in nutrient cycling, and cause accumulation of nutrients in the sediments. Observations within the same site and other East African mangroves (under the PUMPSEA project) indicate negative effects of sewage on the sediment cyanobacterial diversity, with an increase in microalgal abundance. Furthermore, within Mikindani (a sewage impacted site in Tudor creek), high rates of sediment ΣCO2 production indicate a system under stress due to the presence of easily degradable organic matter. (ii) Un-regulated harvesting creates and enlarges canopy gaps, lowering availability of seed bearing trees, altering species composition and stem size distribution due to its selective nature, and lowers regeneration under the enlarged canopy gaps. This strongly lowers recovery rates after major disturbances. (iii) Siltation stands out as a major cause of degradation. Siltation is extrinsic in nature, a result of poor land use practices. This probably makes it a major issue of concern due to its impact on regeneration. A major siltation event, associated with the 1997-1998 ENSO, is widely identified as a cause of enlarged canopy gaps. Little recovery has occurred 10 years after the event due to recurrent anthropogenic pressure. The combined effects of these factors have important implications on growth, productivity and recovery of the mangrove ecosystem. The effects include shifts or changes in mangrove tree species distribution. This has lowered the system functional diversity and response diversity, and therefore ecosystem resilience - viability of the ecosystem. It is recommended that integrated adaptive management, based on sound knowledge of the system is the recommended approach. The participation of stakeholders (government institutions, the private sector and local communities) is crucial for managing peri-urban mangroves for sustainability. Not intervening may only result in a worst case scenario. Especially with the current global financial crisis, more locals will turn to „cheap‟ mangrove firewood.

En vue de l‟augmentation de l‟urbanisation dans les multiples écosystèmes du monde, les mangroves n'étant pas une exception, on observe des obstacles à la viabilité de ces écosystèmes, c.-à-d. leur capacité inhérente de se développer, de s‟étendre ou de récupérer après des perturbations sous des conditions urbaines. Nous avons adapté une approche systémique pour établir la viabilité des mangroves périurbaines de la baie de Tudor à Mombasa, Kenya. Trois aspects importants des mangroves périurbaines sont évalués. Cela inclus (i) les aspects structurels (structure de la végétation et la régénération), (ii) aspects fonctionnels (productivité) et (iii) aspects humains (socio-économiques). Les Chapitres 1 et 2 introduisent l'étude, en exposant brièvement les objectifs et le domaine d'étude. Les chapitres présentent un panorama des adaptations physiologiques des palétuviers et des attributs écologiques qui rendent l‟écosystème de la mangrove unique et hautement adaptable à un environnement intertidal rigoureux et dynamique. Les chapitres suivants exposent l‟étendue et le statut des mangroves au Kenya, leur importance socio-économique et la législation qui cadre leur gestion et conservation.

Les chapitres 3 et 6 décrivent les caractéristiques structurelles et les étapes de la régénération des palétuviers périurbains de la baie de Tudor. Par ordre d'importance des espèces, les palétuviers les plus souvent rencontrés étaient Rhizophora mucronata (Rhizophoraceae) et Avicennia marina (Forssk.) Vierh. (Acanthaceae)&61607; Lumnitzera racemosa Willd. (Combretaceae) n'a pas été rencontrée lors d‟un voyage floristique précédent. La densité d'arbre varie entre 1.264 arbres ha-1 et 1.301 arbres ha-1, ce qui correspond aux moyennes rapportées pour des forêts comparables dans le monde. Cependant, la structure des classes de taille montre une dominance numérique des palétuviers moins développés par rapport aux plus développés. Le pattern de distribution spatiale des adultes et des juvéniles varie considérablement entre les sites et montre presque un modèle uniforme (l'index de Morisita; Iδ << 1) pour les individus adultes. En revanche, pour les juvéniles on retrouve une tendance de distribution groupée (Iδ >> 1). Ce modèle de distribution n'était pas attendu pour une forêt non altérée. La distribution de la régénération des pousses est principalement dictée par la taille des gaps. Ce chapitre montre que les mangroves périurbaines, exploitées et non aménagées, sont structurellement dégradées, ayant des larges gaps caractérisés par une hétérogénéité des conditions édaphiques qui influencent la régénération. Quant aux gaps les plus larges, on retrouve un taux de régénération plus faible. Les gaps élargis et l‟hétérogénéité édaphique imposent de plus longues périodes de fermeture des canopées, en diminuant la régénération et promouvant la mortalité des pousses. Les gaps plus grands (> 60m2) ont des niveaux de régénération plus bas et les gaps intermédiaires (20-50m2) ont une régénération adéquate. L‟occurrence de pousses et de juvéniles de R. mucronata dominent le niveau inférieur de tous les types de couvertures végétales et d‟inondation. Cela confère un avantage à cette espèce sous le régime de perturbation actuel. Les perturbations incluent les eaux usées non traitées, les récoltes non-réglementées et l‟envasement. L'état actuel de la forêt est une phase de récupération, un stade de succession d‟espèces en multiples phases, suite à un événement majeur de perturbation, accompagné d‟une pression anthropogénique récurrente. Cette étude démontre que la composition d‟espèces et donc de la récupération de la forêt de mangrove après une perturbation dépend en partie de l'équilibre entre les perturbations naturelles à grande échelle et humaines à moindre échelle.

Le chapitre 4 évalue la dépendance humaine à l'égard de la mangrove périurbaine. Par des questionnaires et des travaux de terrains, on a constaté que l‟utilisation des questionnaires est délicate. En effet, ceux-ci ciblent des personnes impliquées dans l'exploitation des ressources sensibles. Ceci limite potentiellement sinon empêche le flux de l'information. Le bois de feu est la forme d‟utilisation la plus répandue du bois de mangrove, utilisé dans le cadre de la subsistance et du commerce. Les résultats indiquent qu‟il n‟y a pas de sites de récolte préférés. R. mucronata est l‟espèce la plus récoltée, probablement en raison de sa distribution et facilité d‟accès. La pollution par les eaux usées a appréciation mixte. Certains l‟apprécient pour l‟irrigation de leurs cultures de subsistance, malgré la capacité de filtration des mangroves. L‟étude montre que l‟exploitation des ressources est intense, dans un cadre urbain, dû à une conduite économique et une demande croissante. Par contre, dans le cadre rural, l‟utilisation inclus la production de charbon de subsistance ainsi que commercial. La limitation des moyens de vie dans le cadre rural, couplés à la pauvreté et le besoin d‟énergie domestique bon marché, créent une dépendance des ressources de

mangroves. Ceci a favorisé des niveaux d‟exploitation plus importants, destructeurs et non viables. Les gains associés à ces activités qui dégradent l‟écosystème, sont beaucoup moins importants que les biens et les services offerts par la mangrove. Nos observations, en accord avec d‟autres études, montrent que la gestion de l‟extraction du bois des mangroves dans des zones urbaines n‟est pas une option viable et/ou durable, puisqu‟il entre en conflit avec les fonctions et services essentiels de „filtration‟ et „d’approvisionnement pour l’habitation‟ de la mangrove. Ce phénomène résulte du manque d‟alternatives adéquates et des conflits d‟intérêts des zones urbaines en expansion. Il est recommandé de mettre en place une gestion „adaptative‟ et „participative‟ fondée sur les utilisations et utilisateurs multiples, ainsi qu‟une législation, une éducation et des interventions institutionnelles spécifiques, intégrant les connaissances écologiques locales, afin de faciliter des plans de gestion durable pour les mangroves périurbaines.

Le chapitre 5 présente un aperçu de la productivité de la mangrove périurbaine sous-évaluée, surexploitée et polluée par des eaux usées à travers des études de la litière de trois espèces communes de palétuvier, R. mucronata, A. marina et S. alba. L‟étude couvre une période de deux ans. La chute moyenne annuelle de litière a été estimée à 12 ± 3 t ha-1an-1 pour la totalité du secteur, ce qui correspond aux valeurs de forêts comparables occupant des latitudes similaires. La composition et la quantité de la litière changent fortement avec les saisons. Les taux élevés (ca. 5 ± 1 g DW m2 j-1) s‟observent au cours de la saison sèche (Janvier-Avril), sous le North Easterly Monsoon (NEM).Tandis que les taux inférieurs (ca. 3 ± 0,50 g DW m2 j-1) s‟observent au cours de la saison humide (Juin-Octobre), sous le South Easterly Monsoon (SEM). Il y a des variations significatives entre les espèces. R. mucronata a enregistré le taux annuel le plus élevé 15 ± 3 t ha-1an-1. Par contre, il n‟y a pas de différences significatives entre A. marina et S. alba, (11 ± 3 et 10 ± 5 t ha-1an-1, respectivement). Le niveau de pollution par les eaux usées ne semble pas influencer les taux de production de litière en dépit de la concentration plus élevées des nutriments dans les zones complètement exposées. Le δ15N a varié entre les espèces, A. marina (6,48 ± 0,03‰) et S. alba (6,76 ± 0,24‰) ayant une composition plus élevée que R. mucronata (3,88 ± 0,64‰). Cela implique que la forêt a un cycle de l‟N plus ouvert, favorisant l'accumulation dans le système. Cette étude démontre que l'exposition aux eaux usées ne se traduit pas nécessairement en une productivité élevée des palétuviers, mais peut changer le contenu de nitrogène total des feuilles, probablement en changeant la décomposition de la litière et le cycle des nutriments. Le chapitre 7 présente une synthèse liant les résultats aux implications possibles sur le statut général de l'écosystème des mangroves. Les perturbations principales observées pour les mangroves périurbaines de la baie de Tudor incluent (i) la pollution par les eaux usées domestiques, (ii) la récolte récurrente irrégulière et (iii) l‟envasement annuel pendant la saison des pluies. Nos observations indiquent que: (i) la pollution par les eaux usées non traitées n‟est pas nocive pour les palétuviers, mais peut affecter les conditions édaphiques par l'enrichissement en éléments nutritifs. Les effets de la pollution des eaux usées, quoique non prouvés qualitativement dans notre étude, augmentent la croissance des palétuviers. Ce par une augmentation des quantités de nutriments disponibles pour la formation de biomasse, observée lors de l‟étude de l‟efficacité de résorption des nitrates par les feuilles. Cependant, on rapporte que les eaux usées domestiques non traitées changent le système de décomposition aérobique-anaérobique naturel des mangroves vers un système uniquement anaérobique. Ce qui diminue l‟efficacité du cycle nutritif et engendre l'accumulation des nutriments dans les sédiments. Les observations sur le même site et sur d‟autres mangroves de l‟Afrique de l‟Est (sous le projet PUMPSEA), indiquent des effets négatifs des eaux usées sur la diversité des cyanobactéries du sédiment et une augmentation de l'abondance des micro-algues. En outre, à Mikindani (site affecté par des eaux usées dans la baie de Tudor), les taux élevés de production de ΣCO2 dans le sédiment indiquent un système sous pression (ou sous stress), suite à la présence de la matière organique facilement dégradable. (ii) L‟exploitation non réglementée va créer et agrandir des gaps. En fonction de la nature sélective de l‟exploitation, il y aura une diminution de la disponibilité des arbres produisant des propagules, un changement de la composition des espèces et de la distribution des tailles des arbres. De plus, elle réduit la régénération sous les larges gaps. Cela diminue fortement les taux de rétablissement après d‟importantes perturbations.

(iii) L'envasement est la cause majeure de la dégradation. L'envasement est extrinsèque par nature, parce qu‟il découle de mauvaises pratiques d‟exploitation de la terre. Ce phénomène est probablement le point de concertation majeur, dû à son impact sur la régénération. Un événement d'envasement majeur, lié à l‟ENSO de 1997-1998, est identifié comme étant une cause d‟agrandissement des gaps. Peu de récupération s'est produite lors des dix années qui suivirent l'événement, suite à la pression anthropogène récurrente. Les effets combinés de ces facteurs ont des implications importantes sur la croissance, la productivité et la récupération de l'écosystème des mangroves. Les effets incluent des variations ou des changements de la distribution des espèces de palétuviers. Ceci a diminué la diversité fonctionnelle et la diversité des réponses du système et a donc diminué la résilience de l‟écosystème - la viabilité de l'écosystème. Il est recommandé qu‟une gestion adaptative intégrée, fondée sur la connaissance orale du système, soit la meilleure approche. La participation des décideurs (institutions gouvernementales, secteur privé et communautés locales) est cruciale pour la gestion des mangroves périurbaines. Dans l‟absence d‟intervention, seul le pire scénario peut être envisagé. En particulier avec la crise financière globale actuelle, la population locale se tournera encore plus vers le bois de feu „bon marché‟ de la mangrove.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Doutoramento em Arquitetura Paisagista e Ecologia Urbana - Instituto Superior de Agronomia. Universidade de Lisboa / Faculdade de Ciências. Universidade do Porto / Faculdade de Ciências e Tecnologia. Universidade de Coimbra
Cities in Africa, where the most remarkable forthcoming developments in the global pattern of urbanization are expected, and quite notably in Sub-Saharan cities such as Maputo, are experiencing accelerating population increases. As a consequence of this growth urban infrastructures are being stressed beyond capacity and there is increased pressure on the existent valuable ecosystems. In recent times, and mostly due to foreign intervention, investments have been welcomed into Maputo’s grey urban infrastructure network whereas little attention has been given to green infrastructure. In the city’s coastal plains, the recently constructed Maputo ring road and the Katembe bridge are drawing urban development towards the last stretch of vacant land of the Municipality, compromising the mangrove ecosystems and flood plains of this territory. Based on the hypothesis that mangroves have the potential to become a structuring element for the improvement of resilience in self-produced neighbourhoods on the coastal plains, the aim of this research is to contribute towards the outline of an urban green infrastructure for the coastal areas of Maputo, as a strategy to accommodate current and future urban development challenges, not only as biophysical networks that can create urban socio-ecological networks that improve urban resilience through a stewardship of ecosystems, but also as an ecosystem-based approach for adaptation to climate change. Considering the specific dynamics of Sub-Southern African cities, where research and planning around environmental issues is in very early stages, it is urgent to promote research and design strategies to tackle the problematics of urban development in ecologically sensitive and landscape valuable areas. This research thus expects to anticipate the sustainable development of Maputo, exploring the potential of its coastal landscape for the establishment of an urban green infrastructure
N/A

Sur la côte à ria du littoral du Pará, en Amazonie brésilienne, alternent mangroves, plages et dunes. Les marais maritimes constituent une véritable forêt littorale s’étendant sur près de 2000 km². Cette interface aux limites mouvantes constitue une barrière, empêchant pénétration systématique et installations humaines, mais aussi une zone ressource utilisée par les populations locales pour subsister, grâce à des activités de pêche et de collecte de mollusques et crustacés dont le crabe de mangrove Ucides cordatus. Cet espace s’insère dans la zone côtière, plus peuplée que le reste de l’Etat, et doit faire face aux mutations engendrées par la modernisation et la croissance des échanges. A travers l’étude systémique du littoral où les situations sont très diverses, tant pour ce qui concerne les activités pratiquées que l’intégration à l’espace régional, nous nous intéressons à la question de l’organisation de l’espace. Elle est abordée ici sous différents angles et échelles pour définir ce qui la détermine : milieu physique complexe et original, proximité de l’espace maritime, estuarien ou au contraire terrestre, historique du peuplement et aménagements modernes. Les disparités entre les espaces s’accentuent avec la modernisation, les migrations, la pression démographique et sur les ressources naturelles, ce qui pose la question de la gestion durable des ressources et des espaces. Conflits d’usage, perturbations des milieux, mutations socio-économiques modifient l’organisation des sociétés locales, leur espace de vie et le milieu grâce auquel elles vivent. Différentes stratégies d’adaptation et de gestion permettent de faire face avec plus ou moins de succès à ces mutations
On the ria coastline of the Pará state, in Brazilian Amazonia, we find a succession of mangroves, beaches and sand-dunes. The mangroves there constitute a true coastal forest, covering nearly 2000 km². This interface, marked by its blurred limits, woks simultaneously as a barrier against human systematic penetration and settlement, and as a means of subsistence for the local populations fishing and collecting crustaceans and molluscs. This area, because it is part of the coastal region, more densely populated than the reste of the state, muste endure the changes involved by modernization and growing exchanges. In our study of the coastline as a system, with its immense diversity in terms of men’s working activities or integration within the regional space, we will focus on the question of spatial organization. Our subject wil be dealt with from different angles and on diferent scales, so as to find out what elements influence it, including a complex, unique physical environment, closeness to the land or on the contrary to the sea or estuaries, the history of human settlement, and the road infrastructures. The disparities between the various areas tend to increase with modernization, population pressure, human migration and pressure on the natural ressources, which precisely arouses the question of how to manage them in terms of the latter. The organization of the local human societies, their living space and ressources may change according to the conflicts regarding how to use the land, the perturbations of the environment and the socio-economic mutations. Various strategies may be adopted so as to handle, adapt to and finally cope with the latter more or less successfullly

Les mangroves des Emirats sont situées à la :limite du tropique (24 ° à 26 ° N). Là, elles poussent dans des lagunes et des îles abritées, sous climat aride ou hyper-aride, probablement les sites de mangrove les plus arides du monde. Cependant, aux Emirats comme ailleurs, les activités humaines menacent ces écosystèmes d'un grand intérêt dans une région subdésertique. Curieusement, ce travail semble être la première thèse consacrée aux mangroves du Golfe Persique. Son objectif est d'inventorier et de caractériser les mangroves des Emirats par des relevés de terrain et par la télédétection, en déduisant de cette étude des propositions pour leur protection et leur aménagement. Ce travail peut être divisé en trois parties. Des observations de terrain précises ont été menées sur trois sites-test pour établir des corrélations entre la structure des types de mangrove et les principaux paramètres du milieu. La télédétection est utilisée ensuite pour actualiser les connaissances sur la localisation et la superficie des mangroves des Emirats ; dans cette partie, la recherche est orientée vers l'estimation des capacités des capteurs à haute résolution pour cartographier les communautés de mangrove en milieu aride, en définissant les meilleures bandes et les meilleures méthodes de traitement. Finalement, les résultats obtenus sont utilisés pour proposer un guide pour l'aménagement de ces écosystèmes. Ces résultats consistent notamment en données détaillées sur les effets de l'aridité sur la croissance d'Avicennia marina, ainsi que sur la productivité primaire de ces mangroves (6 à 8 tonnes/ha/an de poids sec). D'autre part, on explique pourquoi les mangroves du Golfe intérieur, qui ont des caractéristiques écologiques différentes de celles du Golfe extérieur, sont constituées de la même espèce : les premiers résultats des recherches en génétique semblent confirmer qu'il s'agit de deux populations différentes. En ce qui concerne la télédétection, nous sommes capables de réaliser des cartes côtières à partir de données HRVIR de SPOT ou ASTER de TERRA dans les bandes visibles, proche infrarouge et moyen infrarouge. Cependant, le traitement numérique des images n'est en aucun cas une technique automatique et standardisée dans les applications concernant le milieu naturel. En dernier lieu, après avoir analysé les impacts de l'industrie pétrolière et d'une croissance démographique et économique spectaculaire, nous proposons quelques recommandations en tenant compte du cadre légal, notamment un programme de sensibilisation. Enfin, la particularité de cette étude est de relier d'une part, les connaissances fondamentales sur la biologie, l'écologie et la dynamique des mangroves des Emirats, d'autre part, les aspects techniques (télédétection) de l'inventaire, du suivi et de la cartographie de ces écosystèmes, et finalement les grandes lignes de plans d'aménagement possibles pour les mangroves des Emirats
Its aim is to survey and characterize the UAE mangrove ecosystems through field investigations and remote sensing, deducing from this study some propositions for their conservation and management. The present work can be devided into three parts. Precise field surveys have been carried out within three test-sites in order to correlate the structure of mangrove types with main environmental parameters. Remote sensing is then used to update the knowledge on the location and areal extent of mangrove ecosystems in UAE ; in this part, the research is oriented to knowing the ability of high resolution sensors for mapping mangrove communities in arid environments, defining the best channels and the best processing methods. Finally, the results obtained are utilised for proposing guidelines for the management of these important ecosystems. These results particularly consist in detailed data on the effects of aridity on Avicennia marina growth, as well as on the primary productivity of these mangroves (6 to 8 tons/ha/year of dry weight). On another hand, it is explained why the mangroves of the inner Gulf and those of the outer Gulf have distinct ecological settings, while bearing only one mangrove species : the first findings related to genetic researches seem to confirm that both populations are distinct. Regarding the use of remote sensing, we are able to produce coastal maps through SPOT-HRVIR and TERRA-ASTER data in the visible, near infra-red and SWIR bands. However, digital image analysis is by no mean an automated and standardized technology when dealing with environmental issues. At the end, after analysing the threats created by oil industry and the spectacular population and economic growths, we propose some recommendations taking into account the legal context, particularly an awareness program. Ultimately, this study has the peculiarity to link fundamental knowledge on the biology, ecology and dynamic process in mangrove ecosystems of the UAE with technical aspects (remote sensing) for the inventory, monitoring and mapping of these ecosystems, and finally with broad lines of possible practical action plans for the management of mangroves, especially in the UAE

Le fonctionnement ecologique et les amenagements agro-sylvicoles des mangroves de guinee sont titubaires d'une dynamique sedimentaire particulierement instable. Celle-ci determine l'evolution des classes d'innondation qui, en depit d'une integration parfois approximative des differents aspects du milieu, constituent le cadre de reference pour une classification des paysages et toute intervention d'amenagement. La physiologie des peuplements et leur translation dans l'espace sont rythmees conjointement par l'evolution morphogenetique du piemont cotier et les variations hydroclimatiques liees a la position latitudinale marginale de la plaine cotiere guineenne. Le degre de stabilite morphodynamique des vasieres conditionne ainsi l'ompact des amenagements et singulierement celui des extensions hydro-agricoles recentes. L'analyse des signatures spectrales fondee sur la comparaison analogique des compositions colorees spot et des photographies aeriennes infrarouge couleur permet de cartographier a moyenne echelle les formations vegetales spontanees et les unites agro-ecologiques qui en derivent. Le traitement informatique des donnees numeriques ameliore la discrimination de certains de ces paysages et precise les correlations entre leur dynamique et l'evolution des domaines continentieux et infralittoraux voisins. Les donnees satellitaires a haute resolution constituent ainsi un outil precieux pour le suivi ecologique des mangroves a forte instabilite morphodynamique
The ecological functioning and the agro-silvical mangement of the guinean mangrove swamps depend on a sedimentary dynamic which is greatly unstable. The latter brings about the evolution of the tidal inondation classes which, in spite of some approximations, form the most useful framework for a classification process and a management scheme. Physiology and habitat change of mangrove communities are closely related both to the continental morphogenic evolution and the hydro-climatic variability in connection with the marginal latitude of the guinean coastal plain. Thus, the unstability of the substrata has a strong influence on the managements impacts, especially those of rice cultivation reclaimed areas which are rapidly extending up to the sea shore. The analysis of spectral signatures based on the analogic comparison between spot colored composite and infrared colour photographs allows the mapping of vegetal and agro-ecological landscape at medium scales. The computer processing techniques help to improve the discrimination between some of these landscapes and to state precisely the correlation between ecosystem dynamicfs and the evolution of backward and foreward environments. High resolution satellite data provide accurate information for the ecological survey of mangroves characterized by unstable conditions of development such as in guinea

Les mattes de procaryotes constituent une niche écologique diversifiée. peu étudié!<..en mangrove et jamais décrjte dans les Antilles. L'objectif de cette thèse est de décrire les procaryotes filamenteux reposant sur le sédiment marin et de caractériser les interactions entre la matte, milieu et entre les différents micro-organismes. Nous avons d'abord caractérisé les micro-organismes majoritaires de la matte par le séquençage de l'ADNr 16S et des hybridations moléculaires (FISH). Il a ainsi été possible de décrire deux nouvelles espèces de Beggiatoaceae dont la structure a été étudiée par microscopie électronique. De plus, afin de caractériser l'environnement chimique de ces bactéries, des capteurs potentiométriques ont été utilisés. Ils ont permis de démontrer que les Beggiaotaceae oxydaient les sulfures en prélevant l'oxygène du milieu, tandis que des analyses de microscopie couplées à de l'EDX ont mis en évidence des réserves de soufre intracellulaires dans ces bactéries. Le séquençage de l'ADNr 16S des cyanobactéries filamenteuses a mis en évidence quatre nouvelles espèces de l'ord~e des Oscillatoriales. Deux d'entre elles, du genre Planktothricoides ont révélé une toxicité positive sur les Artemia sp:, les deux autres ont été identifiées comme proches d'Oscillatoria spongeliae, une espèce symbiotique d'éponge, bien que les coupes uItrafines d'une de ces souches aient montré une morphologie interne proche des Tychonema. L'analyse des données a permis d'étoffer les connaissances sur les communautés microbiennes de mangrove et constitue une base intéressante de travail sur la contribution des micro-organismes au fonctionnement de l'écosystème mangrove dans son ensemble
Procaryotic mats are ecological niches, occuring in many ecosystems. Those structures are little studied in marine mangrove sediment and have never been described in West Indies. The purpose ofthis thesis is to characterize the interactions between the mat and the environment, and between the different filamentous micro-organisms living into the mat. In a first place, we characterized the mainly micro-organisrns of the mat by sequencing 16S rDNA. We confirmed these sequences by molecular hybridization (FISH) with specific probes designed from sequences obtained. Thus, it was possible to describe two new Beggiatoaceae strains, whose structure has been studied by electronic microscopy. Furthemore, we used potentiometric captors in situ and in laboratory, by creating a mesocosm, in order to define the chemical environment where involved these bacteria. These experiences proved that the Beggiatoaceae of the mat oxidized the sulfur taking the oxygen from the medium, while the microscopic analysis coupled with EDX showed intracellular sulfur granules into the bacteria. The study of the filamentous cyanobacteria of the mat highlighted four new cyanobacteria strains, all studied by electronic rmcroscopy. Two of them belongs to Planktothrlcoides genus and showed positive toxicity on Artemia salina. The others species are close to Oscillatorla spongeliae, a sponge symbiont, nevertheless, one ofthem showed an intemal morphology close to Tychonema. The analysis of the different results adduces sorne knowledge about mangrove microbial communities. Furthermore, this study can be used as an interesting base to study the micro-organisms contribution in functioning mangrove ecosystem

Parmi les phénomènes d'origine anthropique impactant les écosystèmes de mangrove, l'apport d'éléments nutritifs issus des eaux usées domestiques est souvent associé à une meilleure productivité végétale. D'autres compartiments du système sont pourtant parfois négativement impactés, notamment la macrofaune benthique dont les représentants sont souvent considérés comme des espèces ingénieurs de l’écosystème. Au cours de cette thèse, nous avons cherché à étudier les réponses écophysiologiques de trois espèces de crabes de mangroves présents dans le Canal du Mozambique, exposés aux apports d’eau usée domestique ou à de l’ammonium, étudié en tant que potentiel proxy d’enrichissement azoté. Différents marqueurs physiologiques et comportementaux ont été mis en place pour répondre à trois objectifs s’appuyant sur des niveaux intégratifs et des échelles spatiales différentes. Dans une première partie, nous avons cherché à compléter les connaissances sur les réponses physiologiques d’une espèce de crabe, Neosarmatium africanum, Sesarmidae occupant la partie haute de la mangrove, parfois directement exposée aux apports d’effluents domestiques sur l’un site d’étude (mangrove de Malamani, Mayotte) en nous focalisant sur un organe métabolique majeur, l’hépatopancréas. Dans une deuxième partie, nous avons cherché à mieux comprendre quelles potentielles réponses physiologiques et comportementales à l’échelle individuelle pouvaient être impliquées dans la modification des communautés de crabes observées dans des zones régulièrement impactées par l’apport d’eau usée domestique. Nous avons pour cela étudié une espèce de crabe violoniste, Paraleptuca chlorophthalmus, Ocypodidae, dont l’abondance diminue drastiquement sur les zones impactées de la mangrove de Malamani. Nos résultats montrent des réponses à court terme (explosion de la consommation d’oxygène, comportement de fuite et d’émersion) qui pourraient devenir délétères lors d’expositions ponctuelles mais chroniques, comme c’est souvent le cas dans le milieu naturel. Enfin, nous avons cherché à comprendre s’il existait une vulnérabilité différentielle face à des variations de salinités et des apports d’éléments nutritifs (ammonium) sur deux espèces de crabes violonistes génétiquement proches mais vivant dans des conditions environnementales opposées : mangrove de Malamani à Mayotte considéré comme écosystème anthropisé et la mangrove d’Europa (îles Eparses, Sud du Canal du Mozambique) considérée comme écosystème pristine. Les résultats indiquent que les crabes de Mayotte, régulièrement exposés à l’eau douce et aux effluents domestiques, semblent plus tolérants aux variations de salinité et développent des acclimatations physiologiques face à l’exposition à l’ammonium, ce que les crabes d’Europa ne développent pas. L’ensemble des résultats renforcent d’une part les connaissances sur la physiologie de ces ingénieurs de l’écosystème, mais permettent également de mieux lier les réponses individuelles obtenues en laboratoire, à celles observées à l’échelle des populations ou des communautés en milieu naturel. Ils encouragent la mise en place d’études concernant le suivi des écosystèmes de mangroves du Canal du Mozambique à travers l’étude d’espèces potentiellement bioindicatrices et permettent de proposer une approche écophysiologique dans le domaine du suivi et de la conservation des milieux naturels
Among the anthropogenic pressures that impact mangrove ecosystems, nutrient inputs from domestic wastewater are often associated with increased plant productivity. However, other compartments of the ecosystem are sometimes negatively impacted, in particular the benthic macrofauna, whose representatives are often considered to be ecosystem engineers. The aim of this study is to analyse the ecophysiological responses of three mangrove crabs living in mangrove forests located in the Mozambique Channel that are typically exposed to domestic wastewater inputs or ammonia-N. These responses could represent potential proxies for nitrogen enrichment. Different physiological and behavioural markers were considered to meet three objectives based on different integrative levels and spatial scales. Firstly, we sought to improve our knowledge on the physiological responses of a crab species, Neosarmatium africanum, Sesarmidae generally occupying the upper part of the mangrove that is directly exposed to domestic effluent inputs in one of our study sites (Malamani mangrove, Mayotte).The focus was mostly on a major metabolic organ, the hepatopancreas. Secondly, we sought to better understand what potential physiological and behavioural responses at the individual scale could be involved in crab community changes observed in areas regularly impacted by domestic wastewater. A fiddler crab species, Paraleptuca chlorophthalmus, Ocypodidae) was studied. For this species abundance is drastically decreased in the wastewater impacted areas of Malamani study site. Short-term responses were obtained: burst of oxygen consumption, escape and emersion behaviour). These effects could become deleterious during acute and/or chronic exposures, as it is often the case in the natural environment. Finally, we sought to understand whether differential vulnerability to salinity variations and increased nutrient inputs (ammonia-N) could occur for two fiddler crab species. These species are genetically related but live in opposite environmental conditions: in anthropized mangrove ecosystem in Mayotte and in a pristine ecosystem (Europa Island located in the southern part of the Mozambique Channel). Data obtained indicate that crabs regularly exposed to freshwater and domestic effluents in Mayotte are more tolerant to salinity variations and develop key physiological acclamatory processes to ammonia-N exposure compared to crabs from the pristine site (Europa). Altogether, this study strengthens our knowledge regarding the physiology of these ecosystem engineers, but also allows us to better link individual responses obtained in laboratory conditions to those observed at the population or community level in the natural environment. This study is paving the way for complementary studies concerning the monitoring of mangrove ecosystems in the Mozambique Channel using potential bioindicator species, and emphasizes the need to consider ecophysiological analyses in the field of monitoring and conservation of natural environments

Le bangladesh est le pays tropical dans lequel les mangroves sont les plus etendues, couvrant environ 4000 km#2 d'un seul tenant. Elles y jouent un role economique fondamental. La teledetection a ete tres largement appliquee dans ce petit pays, notamment pour la constitution d'une base de donnees sur les mangroves. Cette experience peut etre etendue aux mangroves d'autres pays. L'un des objectifs de cette recherche est donc la recherche de l'information existante sur l'ecologie, la sylviculture, les techniques de reboisement et d'amenagement de ces forets au bangladesh. Cette documentation a ete reunie, analysee, synthetisee. Pour la partie teledetection, des travaux complementaires et originaux ont ete faits dans le cadre de la presente recherche, d'autres faisaient partie d'etudes precedentes, de recherches et d'activites operationnelles d'amenagement auxquelles l'auteur a directement participe. Dans ces travaux, photographies aeriennes et donnees satellitaires ont ete utilisees, tant par analyse visuelle que par traitements numeriques. On trouvera dans cette these les resultats obtenus, ainsi qu'une analyse critique confortee par une longue experience de l'auteur puisqu'il a ete directement implique dans les travaux d'amenagement forestier des mangroves ainsi que dans les activites de teledetection au bangladesh, en tant que directeur du sparso (centre d'etudes spatiales du bangladesh)

Cinq localisations de mangrove de la zone equatoriale font l'objet de cette etude : trois le long de la cote de la guyane francaise et deux en indonesie. Les caracteristiques du developpement de ces mangroves sont differentes du point de vue fluviosite, sequence vegetales, geomorphologie et geologie de l'arriere pays. Les sediments mangroves sont constitues essentiellement par des particules argileuses et limoneuses qui sont deposees par l'energie de la maree. Les sables sont rares et se trouvent particulierement dans la zone ou il y a l'influence de l'energie fluviatiles ou celle des vagues. L'ensemble des sediments est relativement riche en matiere organique d'origine vegetale. Apres une etude comparative des sediments, on determine grace a la mineralogie et geochimie un caractere commun essentiel : une origine detritiques preponderante de ces sediments. La quantite des mineraux authigenes (pyrite, halite et jarosite) est peu importante. Cependant qualitativement, ces mineraux sont le reflet du climat regional

Investigations on the biodiversity in relation to conservative and non-conservative parameters in the Mangalavanam mangrove ecosystem, located in the northern fringes of Cochin City have been carried out from January to June 2002. The mangrove ecosystem is regularly under tidal influence and hence submergence and emergence of land takes place depending on the tidal amplitude. The average dissolved oxygen of the water was found to be 3.5ml/l despite the fact, phytoplankton was abundant in the ecosystem. It reveals that respiratory demand of the aquatic biota has exceeded the photosynthetic oxygen production. The indirect relationship exhibited by the quantity of phytoplankton and oxygen is attributed to anthropogenic activities, which resulted in to the eutrophication of the mangrove ecosystem. The general nutrient load was at a higher level. The macrophytic vegetation was dominated by A^icennia marina, Rhizdphora mucronata and Acanthus ilicifolius. The presence of Avicennia and Acanthus in majority of the area that showed decrease in salinity and more freshwater influx. The phytoplankton community was dominated by djatoms represented Naviculaceae followed by Coscinodisceae, which Is evidenced by the presence of high quantity of silicate. The Zooplankton was dominated by copepods. Benthic community is dominated by the infauna such as polychaetes and decapods. Juveniles of common brackish water fishes. Chanos spp., Liza spp., Etroplus spp., Silago spp., Lethrinus spp. and Lutjanus spp., and species of crustaceans like Penaeus spp., Metapenaeus spp., Macrobrachium spp., Acetes spp., Metaplex spp., Sesarma spp., Uca spp., and Scylla spp., have been found to be the residents of the mangrove ecosystem. Avian fauna comprises mostly little cormorants (Phalactocorax niger) and black crowned night heron (Nycticorax nycticorax). Other arboreal fauna is dominated by Indian flying fox (Pteropus giganteus). An evaluation on the biodiversity of the mangrove ecosystem in the light of the present investigations reveals that species diversity Is less, but moderate population density of available species could be observed. To put It In a nutshell, human interventions on the environment has been detrimental and a general degradation of the ecosystem has been evidenced by the emergence of terrestrial vegetation and shrinking of the true mangrove areas.

Cet ouvrage abondamment illustre (194 figures, 94 photos) se divise en trois livres. Le livre un est consacré à l'étude des composantes et des facteurs des marais maritimes du Gabon et de Madagascar : climat, hydrologie, géomorphologie, sols, flore et faune. Le livre deux décrit quelques-uns des marais maritimes situes sur la côte occidentale de Madagascar et au nord-ouest du Gabon. Le livre trois examine les grands problèmes de dynamique des marais soulevés dans l'étude régionale : réseaux de chenaux, mangrove, transitions entre mangrove et foret marécageuse, tannes, exploitation et aménagements (ressources forestières, pèche, agriculture, saliculture, aquaculture). L'ouvrage s'achevé sur une tentative de typologie des marais maritimes tropicaux qui repose sur la part relative dans les marais, de la mangrove, des tannes et des marécages d'arrière-mangrove
This work abundantly illustrated (194 figures, 94 pictures) is divaded in three books. The book one is consecrated at the study of thedifferent elements and factors of the tidal marshes of gabon and madagascar : climate. Hydrology, geomorphology, soils, flora and fauna. Thebook two describe many tidal marches located along the western coast of Madagascar and in the north-west region of Gabon. The book three examine the chief problems of dynamics : tidal creeks systems, mangrove forest, transitions between and swamp forest, "tannes" (salt marshes), exploitation (forest exploitation, fisheries, rice cultivation, salt ponds, aquaculture). The work finish with a attempt of typology of tropical tidal marshes resting on the relative part of manguals, tannes and swamps

Mangroves are defined as those trees and shrubs growing between high water of spring tide and the mean sea level where the wave action is feeble (Macnae, 1968). The term mangroves is generally used for both the vegetative colonisation as well as individual species. Singh et. al. (1986) defined mangroves as characteristic littoral plant formations of tropical and subtropical protected coast lines. They are salt tolerant forest ecosystems, of tropical and subtropical intertidal regions of the world. The distribution and restriction of mangroves in the sub-tropical regions are influenced by the pattern of warm water and cold water currents. Soft mud, sand bars and protected topography of the bays, lagoons and estuaries provide shelter from wave action and thereby enhance luxuriant growth of mangrove vegetation. The geographical occurrence of the mangroves are found in the West Africa, Atlantic U.S.A., Pacific America, East Africa, Australia, Asia and Oceanica, (Krishnamurthy et.al., 1979 and Blatter, 1905).

Alors que la Guadeloupe possède la plus grande bordure littorale de mangroves des Petites Antilles, la microfaune et la microflore bactérienne marine associées à cet écosystème sont très mal connues. Pourtant, ces diverses communautés de micro-organismes sont à la base du réseau trophique des sédiments marins de mangrove. En effet, grâce à leurs activités basées sur des processus hétérotrophes, ces micro-organismes vont permettre de dégrader la litière constituée de feuilles et branches de palétuviers tombées à la surface du sédiment. En condition anoxique, la dégradation des substrats végétaux par des bactéries sulfato-réductrices entraine la production de sulfures qui vont soutenir l’activité de bactéries chimiosynthétiques. Les protistes ciliés sont des micro-organismes eucaryotes unicellulaires caractérisés par la présence de cils sur la surface cellulaire et appartenant au micro-zooplancton. Leur mode de nutrition basé sur la phagocytose permet non seulement de favoriser la reminéralisation de la biomasse microbienne, ce qui augmente le transfert de nutriments à d'autres organismes du réseau trophique, mais facilite surtout l’émergence de nombreuses associations symbiotiques. Les résultats obtenus durant cette thèse ont permis de mettre en évidence la présence d’associations symbiotiques entre des bactéries sulfo-oxydantes ou hétérotrophes et des espèces de protistes ciliés faisant parties du périphyton de mangrove
While Guadeloupe has the largest coastal edge of mangroves in the Lesser Antilles, the microfauna and marine bacterial microflora associated with this ecosystem are very poorly understood. However, these diverse communities of microorganisms are at the base of the marine mangrove sediment food web. Indeed, thanks to their activities based on heterotrophic processes, these micro-organisms will make it possible to degrade the litter composed of mangrove leaves and branches that have fallen to the surface of the sediment. In anoxic conditions, the degradation of plant substrates by sulfate-reducing bacteria leads to the production of sulfides that will support the activity of chemosynthetic bacteria. Ciliates protists are unicellular eukaryotic microorganisms characterized by the presence of cilia on the cell surface and belonging to micro-zooplankton. Their phagocytosis-based nutrition not only promotes the remineralization of microbial biomass, which increases the transfer of nutrients to other organisms in the food web, but also facilitates the emergence of many symbiotic associations. The results obtained during this thesis allowed to highlight the presence of symbiotic associations between sulfur-oxidizing or heterotrophic bacteria and ciliates protist species that are part of the mangrove periphyton

The total mangrove area cover in South Africa is 1631.7 ha, with the largest area cover in a few estuaries in the KwaZulu-Natal Province (1391.1 ha) and the remainder recorded in the Eastern Cape Province with 240.6 ha. This represents 0.05 percent of Africa‟s mangrove area cover and although small adds irreplaceable value to the biodiversity of South Africa. Mangroves are threatened by over-utilization through harvesting for firewood and building materials as well as excessive browsing and trampling by livestock. The objective of this study was to investigate the response of mangroves to different stressors from natural change as well as anthropogenic pressures. This was done by identifying pressures, measuring area cover, population structure and environmental parameters such as sediment characteristics. Mangroves in 17 estuaries along the east coast were investigated. Population structure and the area covered by mangroves in 2011/2012 were compared with data from the same area for 1999. Detailed studies were conducted in St. Lucia Estuary to investigate the response of mangroves to reduced tidal flooding; mangrove expansion at a latitudinal limit in a protected area at Nahoon Estuary was studied and the effect of cattle browsing on mangroves was measured at Nxaxo Estuary. The St. Lucia Estuary (28°S; 32°E) represented a unique study site as the mouth has been closed to the sea since 2002 and the mangrove habitats have been non-tidal. St. Lucia Estuary is both a Ramsar and World Heritage site and therefore understanding the response of mangroves to changes in the environment is important. In 2010 sediment characteristics and mangrove population structure were measured at four sites which were chosen to represent different salinity and water level conditions. The site fringing the main channel had the highest density of mangrove seedlings and saplings. The dry site had a lower density of mangroves with mostly only tall adult trees and few saplings. Mangrove tree height and density increased at sites with high sediment moisture and low surface sediment salinity. Few seedlings and saplings were found at sites with dry surface sediment and high salinity. Long term data are needed to assess the influence of mouth closure on recruitment and survival of the mangrove forest at St. Lucia Estuary; however this study has shown that sediment characteristics are unfavourable for mangrove growth at sites now characterized by a lack of tidal flooding. It is not known when exactly the mangroves were planted in Nahoon Estuary (32°S; 27° E), East London, but it is suspected that this was in the early 1970s. Avicennia marina (Forrsk.)Vierh. was planted first, followed a few years later by the planting of Bruguiera gymnorrhiza (L.) Lam. and Rhizophora mucronata (L.) among the larger A. marina trees. Surprisingly the mangrove population appears to be thriving and this study tested the hypothesis that mangroves have expanded and replaced salt marsh over a 33 year period. This study provides important information on mangroves growing at higher latitudes, where they were thought to not occur naturally due to lower annual average temperatures. It further provides insights on future scenarios of possible shifts in vegetation types due to climate change at one of the most southerly distribution sites worldwide. The expansion of mangroves was measured over a 33 year period (1978 - 2011) using past aerial photographs and Esri ArcGIS Desktop 10 software. In addition, field surveys were completed in 2011 to determine the population structure of the present mangrove forest and relate this to environmental conditions. The study showed that mangrove area cover increased linearly at a rate of 0.06 ha-1 expanding over a bare mudflat area, while the salt marsh area cover also increased (0.09 ha-1) but was found to be variable over time. The mangrove area is still small (< 2 ha) and at present no competition between mangroves and salt marsh can be deduced. Instead the area has the ability to maintain high biodiversity and biomass. Avicennia marina was the dominant mangrove species and had high recruitment (seedling density was 33 822 ± 16 364 ha-1) but only a few Bruguiera gymnorrhiza and Rhizophora mucronata individuals were found (< 10 adult trees). The site provides opportunities for studies on mangrove / salt marsh interactions in response to a changing climate at the most southern limit of mangrove distribution in Africa. This research has provided the baseline data, permanent quadrats and tagged trees to be used in future long-term monitoring of population growth and sediment characteristics. At Nxaxo Estuary (32°S; 28°E) the response of mangrove trees (Avicennia marina) to cattle browsing and trampling was investigated by using cattle exclusion plots. Exclusion plots were established by fencing in five 25 m2 quadrats and adjacent to each experimental quadrat a control quadrat (not fenced in, 25 m2) was set-up. Trees were tagged and measured annually from 2010 to 2012. Sediment salinity, pH, moisture, organic content, compaction as well as sediment particle size was also measured in each quadrat. Sediment characteristics did not vary between control and experimental plots but did show changes between the years. The mangrove trees in the cattle exclusion plots grew exponentially over a period of two years. There was a significant increase in mean plant height (5.41 ± 0.53 cm), crown volume (0.54 ± 0.01 m3) and crown diameter (7.09 ± 0.60 cm) from 2010 to 2012. Trees in the control plots had significantly lower growth (p < 0.05). There was a decrease in plant height (-0.07 ± 0.67cm1) and only small increases in crown volume (0.14 ± 0.1 m3) and crown diameter (2.03 ± 2.61 cm). The research showed that browsing on mangroves by cattle stunts growth and causes a shrubby appearance as a result of coppicing. The browsed trees were dwarfed with horizontal spreading of branches and intact foliage close to the ground while the plants in the cattle exclusion plots showed an increase in vertical growth and expansion. In the cattle exclusion plots there was a significantly higher percentage of flowering (67 percent) and fruiting (39 percent) trees in 2012 compared to the control sites where 34 percent of the plants were flowering and 5.4 percent of the plants carried immature propagules. Observations in the field also indicated that cattle had trampled a number of seedlings thus influencing mangrove survival. The study concluded that browsing changes the morphological structure of mangrove trees and reduces growth and seedling establishment. This is an additional stress that the mangroves are exposed to in rural areas where cattle are allowed to roam free. Seventeen permanently open estuaries provide habitat for mangrove forests along the former Transkei coast. This part of the Eastern Cape is mostly undeveloped and difficult to access. Mangrove area cover, species distribution, population structure and health of the mangrove habitat were compared with results from previous studies in 1982 and 1999. The mangrove Bruguiera gymnorrhiza had the densest stands and was widely distributed as it was present in 13 of the 17 estuaries. Avicennia marina was dominant in those estuaries which had the largest area cover of mangroves and was present in 10 estuaries, while Rhizophora mucronata was rare and only present in five estuaries. Anthropogenic and natural impacts were noted within the mangrove habitats in each of these estuaries. Harvesting of mangrove wood, livestock browsing and trampling and footpaths occurred in most of the estuaries (> 70 percent). It was observed that browsing on trees resulted in a clear browse-line and browsing on propagules mainly by goats resulted in reduced seedling establishment in most of the estuaries except those in protected areas. Mangroves had re-established in estuaries where they had been previously lost but mouth closure due to drought and sea storms resulted in the mass die back of mangroves in the Kobonqaba Estuary. There was a total loss of 31.5 ha in mangrove area cover in the last 30 years and this was a total reduction of 10.5 ha (11 percent) for every decade. This is high considering that the present total mangrove area cover is only 240.6 ha for all the Transkei estuaries. In this study it was concluded that the anthropogenic impacts such as livestock browsing and trampling as well as harvesting in these estuaries contributed most to the mangrove degradation as these are continuous pressures occurring over long periods and are expected to increase in future with increasing human population. Natural changes such as sea storms occur less frequently but could result in large scale destruction over shorter periods. Examples of these are mouth closure that result in mangrove mass mortality as well as strong floods which destroy forest by scouring of the banks.

Estudos recentes demonstram a eficÃcia do manguezal em reter nutrientes e, em especial, a capacidade dos componentes minerais do seu solo em tamponar elevados teores de fÃsforo. Em geral, os solos dos manguezais tÃm sido considerados como importantes sumidouros de nutrientes devido a sua grande capacidade de depuraÃÃo de efluentes. Entretanto, dependendo das condiÃÃes geoquÃmicas existentes, esses solos podem funcionar como fonte de fÃsforo para outros ambientes e/ou para as Ãguas costeiras. Tendo em vista que o comportamento geoquÃmico do fÃsforo, bem como seu papel na eutrofizaÃÃo dos corpos d'Ãgua, à melhor avaliado atravÃs do comportamento de suas diferentes fraÃÃes, o presente trabalho visa realizar um fracionamento das diferentes formas de fÃsforo em manguezais impactados por distintos efluentes. O objetivo da presente dissertaÃÃo à estudar trÃs Ãreas a fim de se avaliar como as atividades impactantes interferem no processo de ciclagem de nutrientes (com especial Ãnfase na dinÃmica das formas de fÃsforo) e, como o manguezal suporta o estresse ocasionado por estas atividades. AlÃm disso, se avaliarà o potencial de eutrofizaÃÃo de cada uma das atividades antrÃpicas. Levando-se em consideraÃÃo os impactos que esses ambientes sofrem em consequÃncia de distintas atividades, foram estabelecidas as seguintes Ãreas de estudo: um manguezal impactado por efluentes de carcinicultura; um manguezal impactado por efluentes urbanos; e uma Ãrea controle localizada em uma Ãrea preservada que ainda encontra-se pouco afetada por impactos antrÃpicos. Nas amostras foram determinados pH, Eh, salinidade, granulometria e teores totais de C e P. AlÃm disso, foi realizada a extraÃÃo seqÃencial de fÃsforo que permite a diferenciaÃÃo de 7 fraÃÃes: P trocÃvel (NaCl-P); P associado a Ãxidos de Fe (FeP); P orgÃnico (AH-P); fÃsforo ligado a hidrÃxidos de Al (Al-P); P associado a compostos de cÃlcio (Ca-P); fÃsforo associado à matÃria orgÃnica refratÃria (P-RES) e fÃsforo nÃo reativo (P-NR). Os resultados obtidos indicam que o descarte de efluentes nos manguezais aumenta a quantidade de fÃsforo nesses ambientes, principalmente nas formas orgÃnicas; o fÃsforo ligado aos compostos de cÃlcio à a principal fraÃÃo inorgÃnica nesses ambientes. Palavras-chave: ciclagem de nutrientes; extraÃÃo sequencial; carcinicultura; efluente domiciliar
Recent studies demonstrated the efficacy of mangrove retaining nutrients and, in particular, the ability of the mineral component of the buffer in its high soil phosphorus levels. In general, the mangroves have been considered as important sinks of nutrients due to its high capacity purification of effluents. However, depending on the geochemical conditions exist, these soils can act as a source of phosphorus to other environments and / or coastal waters. Given that the geochemical behavior of phosphorus and its role in eutrophication of water bodies, is best measured by the behavior of its different fractions, this paper aims at a fractionation of the different forms of phosphorus in wetlands impacted by different effluent. The objective of this project is to study three areas in order to assess how activities impacting interfere in the process of nutrient cycling (with special emphasis on the dynamics of phosphorus forms) and, as the marsh supports the stress caused by these activities. Also, if you evaluate the potential for eutrophication of each human activities. Taking into consideration the impact that these environments suffer as a result of separate activities, were established the following areas of study: a marsh impacted by effluents from shrimp, a marsh impacted by effluents, and a control area located in a preserved area that still finds is little affected by human impacts. The samples were determined pH, Eh, salinity, grain size and the total content of C and P. In addition, extraction was performed sequentially phosphorus which allows differentiation of fractions 7: P exchangeable (NaClP), P associated with iron oxides (Fe-P); organic P (AH-P), the bound phosphorus hydroxides Al (Al-P), P associated with compounds of calcium (Ca-P); phosphorus associated refracting matter (P-RES) and unreacted phosphorus (P-NR). The results indicate that the discharge of effluents in mangrove increases the amount of phosphorus in these environments, especially in organic form, the phosphorus bound to carbonate is the major inorganic fraction in these environments.

Tese (doutorado)—Universidade de Brasília, Instituto de Geociências, Programa de Pós-Graduação em Geologia, 2016.
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Zonas costeiras do mundo afora estão sob forte pressão da contaminação antrópica, uma vez que a população global e as atividades econômicas concentram-se ao longo das costas e dos estuários. A ameaça de contaminantes nestes ecossistemas torna imperativo o desenvolvimento de ferramentas capazes de detectar mudanças biogeoquímicas no intuito de auxiliar a prevenção, o monitoramento e a predição de riscos em estudos ambientais. Assim, esta tese investiga a geoquímica isotópica do Zinco (Zn) de forma a desenvolver uma ferramenta capaz de traçar fontes naturais e antrópicas, identificar processos biogeoquímicos e possibilitar o biomonitoramento de contaminação metálica em áreas costeiras e mangues. Para este fim, composições isotópicas de Zn foram determinadas em várias amostras naturais coletadas na baía de Sepetiba (sudeste do Brasil), um estuário lagunar impactado por uma costa industrializada próximo à cidade do Rio de Janeiro. Esta baía constitui um laboratório natural ideal para avaliação do sistema isotópico de Zn para questões ambientais, pois apresenta importantes ecossistemas de interesse comercial e ecológico – estuários, mangues e planícies de maré – ameaçados pela contaminação de uma antiga atividade galvânica e outras fontes difusas. As amostras coletadas incluem testemunhos de sedimento, sedimentos superficiais de mangue, folhas de árvores de mangue, tecido mole de moluscos bivalves (ostras e mexilhões) e rochas. Minérios do depósito de Vazante (Minas Gerais, Brasil), também foram coletadas para representar a matéria-prima utilizada na antiga atividade galvânica. Primeiramente, um trabalho laboratorial inicial estabeleceu um método acurado e preciso para determinações isotópicas de Zn em amostras naturais por espectrometria de massa com plasma indutivamente acoplado e multi-coletor (MC-ICP-MS). Análises espaciais e temporais dos resultados das composições isotópicas de Zn de amostras de sedimento e rocha se ajustam à um modelo de mistura entre três membros finais: i) materiais continentais carreados pelos rios; ii) fontes marinhas; e iii) uma fonte antropogênica principal associada a antigos rejeitos de galvanoplastia lançados na baía. Testemunhos de sedimento coletados na planície lamosa mostraram altas correlações entre as composições isotópicas de Zn e fator de enriquecimento de Zn, sugerindo (i) uma boa preservação dos registros isotópicos de fontes naturais e antrópicas, e (ii) ausência de fracionamento isotópicos significativos durante o transporte de sedimentos ou em reações diagenéticas pós-deposição no sistema estuarino. O testemunho de sedimento coletado em um mangue localizado na zona impactada pelos antiga atividade galvânica apresentou níveis de Zn acima de 4% (peso seco) e preservou as assinaturas isotópicas dos rejeitos da galvanoplastia. Entretanto, há evidências de que processos biogeoquímicos promovidos por processos hidrodinâmicos, biotubarção e rizosfera podem alterar sutilmente as assinaturas isotópicas em algumas camadas do perfil. Cálculos baseados neste modelo de mistura quantificaram contribuições da principal fonte antropogênica variando de valores desprezíveis em períodos pré-industriais até 80% durante períodos da atividade eletrogalvânica entre as décadas de 60 e 90. A sistemática dos isótopos de Zn de bivalves não foi associada a processos de mistura de fonte. Em vez disso, suas assinaturas bioisotópicas parecem estar relacionadas às diferentes rotas de bioacumulação, i.e, via incorporação da fase dissolvida ou particulada. A hipótese é que na zonas severamente impactadas pelos antigos rejeitos da galvanoplastia, os bivalves incorporam altas concentrações de Zn na fase dissolvida através das brâquias, enquanto fora desta zona, estes organismos incorporam o Zn lábil ligado ao material partículado durante a digestão. Assinaturas isotópicas de Zn de folhas também não permitiram a identificação de fontes por causa do significativo fracionamento isotópico durante a incorporação do Zn pelas raízes. Folhas de ambientes contaminados apresentaram padrões isotópicos de Zn diferentes dos padrões encontrados em folhas de áreas pouco ou não contaminadas. Estes padrões podem estar associados à ativação de mecanismos de tolerância pelas árvores do mangue onde as concentrações de Zn atingem concentrações tóxicas. Em conclusão, as composições isotópicas de Zn de amostras abióticas como sedimentos são efetivas para detectar mudanças biogeoquímicas desencadeadas por atividades antrópicas e, portanto, podem ser úteis para dar suporte à prevenção, ao monitoramento e à predição de riscos em áreas impactadas pela contaminação metálica. Amostras biológicas de moluscos bivalves e folhas de árvores de mangue não são adequadas para traçar fontes, porém, os distintos padrões isotópicos de Zn encontrados para amostras de ambientes altamente contaminados são promissores para aplicar isótopos de Zn como biomarcadores de reações metabólicas e efeitos fisiológicos associados à contaminação metálica. Futuras investigações são necessárias para compreender as relações entre a especiação de Zn, mecanismos de incorporação e as assinaturas bioisotópicas de tecidos de bivalves e folhas.
Coastal areas worldwide are under strong pressure from anthropogenic contamination, as most of the global population and of economic activities are concentrated along the coasts and estuaries. The threaten of contaminant releasing into these ecosystems makes imperative the development of tools capable of detecting biogeochemical changes in order to help prevention, monitoring and prediction of risks in environmental studies. In this way, this thesis investigates the isotope biogeochemistry of Zinc (Zn) in order to develop a tool capable of tracing natural and anthropogenic sources, identifying biogeochemical processes and enabling the biomonitoring of metal contamination in coastal areas and mangroves. To this end, Zn isotopes compositions were determined in several natural samples collected from Sepetiba bay (southeastern Brazil), an estuarine-lagoon impacted by an industrialized coastal area near Rio de Janeiro. This bay constitutes an ideal natural laboratory for evaluating the Zn isotopic system to environmental issues, since it hosts important ecosystems of commercial and ecological interest – estuaries, mangroves and tidal flats – threaten by the metal contamination resultant of old electroplating activity and other anthropogenic diffuse sources. The collected samples include sediment cores, surface mangrove sediments, suspended particulate matter (SPM), leaves of mangrove’s trees, tissues of bivalve mollusks (oysters and mussels) and rocks. Ores from Vazante deposit, Brazil were collected to represent the raw material used in the old electroplating industry. Firstly, an initial laboratory work established a method for accurate and precise determinations of Zn isotope compositions in natural samples by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Spatial and temporal analysis of Zn isotope compositions of sediment and rock samples fits well in a model of mixing between three main end-members: i) continental materials brought via rivers; ii) marine sources; and iii) a major anthropogenic source associated to the old electroplating wastes released into the bay. Sediment cores collected in the mud flat showed high correlation between Zn isotope compositions and Zn enrichment factors, suggesting (i) good preservation of isotopic records of natural and anthropogenic sources and (ii) no significant isotopic fractionation during sediment transport or as a result of diagenetic reactions post-deposition in the estuarine system. The sediment core sampled from a mangrove located in the zone impacted by the old electroplating activity presented levels of Zn up to 4% (dry weight) and preserved the isotopic signatures of electroplating wastes. However, there is evidence that biogeochemical processes triggered by hydrodynamics, bioturbation or rhizosphere processes slightly changed the isotopic signatures in some layers. Calculations based in this mixing model quantified contributions of the major anthropogenic source of Zn, ranging from negligible values in the pre-industrial period to nearly 80% during periods of electroplating activities between the 60’s and 90’s. The Zn isotope systematics of mollusc bivalves were not associated to mixing process of sources. Instead, these bioisotopic signature seems related to different routes of bioaccumulation, i.e. uptake via dissolved or particulate phase. It is hypothesized that in the zone heavily impacted zone by old electroplating wastes, the bivalves incorporate the high levels of Zn in the dissolved phase though the bivalve gills, while outside this zone, these organisms incorporate the labile Zn bound to particulate matter during the gut digestion. Zinc isotopic signatures of leaves did not also allowed identification of sources due to the significant isotopic fractionation during Zn uptake by the roots. Leaves of sites highly contaminated presented different Zn isotopic patterns of those of low or no contaminated sites. These patterns may be associated to activation of tolerance mechanisms of mangrove’s trees where Zn reach toxic levels. To conclude, Zn isotopes compositions of abiotic samples such as sediments are effective to detect biogeochemical changes triggered by anthropogenic activities and, therefore, can be useful to support prevention, monitoring and prediction of risks in coastal sites impacted by metal contamination. Biological samples of mollusc bivalves and leaves of mangrove’s trees are not suitable to sources tracing, but the distinct isotopic patterns of Zn found for those samples from sites highly contaminated are promising as biomarkers of metabolic pathways and physiological effects associated to metal contamination. Future investigations are required to constrain the relationships among Zn speciation, uptake mechanisms and the Zn bioisotopic of leaves and bivalve tissues.
Les zones côtières du monde entier sont sous fort pression de contamination anthropique comme conséquence de la concentration de la plupart de la population mondiale et des activités économiques le long des côtes et des estuaires. La menace de contaminant sur les écosystèmes rend primordial le développement d’outils capable de détecter les modifications biogéochimiques en vue d’aider dans la prévention, la gestion, et la prédiction de risques dans les études environnementales. Dans ce but, cette thèse étudie la biogéochimie des isotopes du Zinc (Zn) en vue de développer un outil capable de tracer les sources naturelles et anthropiques, d’identifier les processus biogéochimiques et de permettre à la biosurveillance de la contamination par les métaux dans les zones côtières et les mangroves. A cette fin, les compositions isotopiques du Zn ont été déterminées à plusieurs échantillons naturels prélevés dans la baie de Sepetiba (au sud-est du Brésil), un estuaire lagunaire affecté par une côte industrialisée située près de Rio de Janeiro. Cette baie constitue un laboratoire naturel idéal pour valider le système isotopique du Zn. En effet, cette zone héberge des écosystèmes d’intérêt commercial et écologique –estuaire, mangrove, estran- menacés par la contamination d’une ancienne activité de galvanoplastie, et d’autres sources diffuses. Les échantillons collectés comprennent des carottes de sédiments, des sédiments de la superficie des mangroves, des matériaux particulaires en suspension (SPM), des feuilles provenant d’arbres de mangrove, des tissus de mollusques bivalves (huîtres et moules) et des roches. Minéraux de dépôt de Vazante (Brésil) ont été collecté pour representé matière première utilisée par l’industrie de la galvanoplastie. Tout d’abord, un travail initial de laboratoire a établi une méthode exacte et précise pour les déterminations isotopiques Zn en échantillons naturelles par spectrométrie de masse avec plasma couplé par induction et multicollecteur (MC-ICP-MS). Des analyses spatiales et temporelles des compositions isotopiques du Zn des échantillons de sédiments et de roches s’ajustent bien à un modèle de mélange entre trois principales extrémités : i) les matériaux continentaux charriés par les rivières ; ii) les sources marines ; et iii) une source anthropique majeure associée aux anciens déchets de galvanoplastie jetés dans la baie. Les carottes de sédiment collectées dans la vasière ont montré une haute corrélation entre la composition isotopique du Zn et le facteur d’enrichissement du Zn. Ceci suggère : i) une bonne préservation du registre isotopique des sources naturelle et anthropique, ii) l’absence de fractionnement isotopique significatif durant le transport de sédiments ou durant les réactions diagénétiques pos-dépositions dans le système estuarien. La carotte de sédiments collectée dans la mangrove, située dans la zone impactée par l’ancienne activité galvanoplastique a présenté des concentrations de Zn au-dessus de 4% (pèse sec) et a préservé les signatures isotopiques des déchets de la galvanoplastie. Cependant, il est évident que les processus biogéochimiques déclenchés par les processus hydrodynamiques, par la bioturbation, et par la rhizosphère peuvent altérer les signatures isotopiques de certaines couches de sédiment. Les calculs basés sur ce modèle de mélange quantifient les contributions de la principale source anthropique variant de valeurs négligeables en périodes préindustrielles jusqu’aux 80% pendant les périodes d’activités de galvanoplastie entre les années 60 and 90. La systémique des isotopes du Zn des mollusques bivalves n’est pas associée au processus de mélange des sources. Au lieu de cela, ces signatures bioisotopiques semblent liées à différentes routes de bioaccumulations, i.e. par l’incorporation de phase dissoute ou de particules. L’hypothèse est que, dans les zones sévèrement impactées par les anciens rejets de galvanoplastie, les bivalves incorporent les hautes concentrations du Zn sous forme dissoute via les branchies. Cependant, hors de cette zone, ces organismes incorporent via la digestion le Zn labile. Les signatures isotopiques du Zn des feuilles également n’ont pas permis l’identification des sources en raison du fractionnement isotopique significatif au cours de l’incorporation du Zn par les racines. Les feuilles des sites hautement contaminé ont montré des standards isotopiques du Zn diffèrent des feuilles des sites peu ou non contaminé. Ces standards peuvent être associés à l’activation de mécanismes de tolérance par les arbres de la mangrove où le Zn atteint des niveaux toxiques. En conclusion, les compositions isotopiques du Zn des échantillons abiotiques, comme les sédiments, permettent de détecter les changements biogéochimiques déclenchés par des activités anthropiques. Ainsi, elles sont utiles pour donner des supports á la prévention, á la gestion, et á la prédiction de risques dans les zones impactées par la contamination métallique. Échantillons biologiques de mollusques bivalves et de feuilles provenant d’arbres de mangroves ne sont pas appropriés pour tracer les origines du Zn. Cependant, les distinctes compositions isotopiques du Zn des échantillons collecté aux sites hautement contaminé sont prometteurs pour l’application de ces isotopes comme marqueurs biologiques de réactions métaboliques et de réponse physiologiques. Toutefois, il faut plus de recherches afin de comprendre la relation entre la speciation du Zn, mécanismes de d’incorporation et les signatures bioisotopiques de cet élément dans les tissus de bivalves et feuilles.

Les mangroves présentent des fonctions et valeurs écologiques, socio-économiques et d’atténuation du changement climatique majeures et vitales pour la population littorale dans le monde et à Madagascar. Leur richesse en fait des milieux intensément exploités, les soumettant à de fortes pressions naturelles et anthropiques. Pourtant à Madagascar « les mangroves sont très mal comprises et nous n'avons pas en main les éléments nécessaires à un bon diagnostic » alors qu’on associe celles de la région Sud-ouest à un état de perpétuelle régression. Cette thèse a pour objectifs l’identification, la cartographie et la quantification de la dynamique d’évolution (depuis 1949) des mangroves de 5 sites du Sud-Ouest : Manombo-Fitsitike, Ambondrolava, Ankiembe, Sarodrano et Andriambe. Elle vise aussi à diagnostiquer les différents facteurs d’évolution en faisant la part des pressions anthropiques et naturelles. Pour atteindre ces objectifs, deux approches ont été adoptées : la géomatique se basant sur l’analyse diachronique d’images Spot de 1987, 1998, 2012 et 2014 associées à des photos aériennes de 1949 et des recherches sur terrain avec des inventaires floristiques, des mesures physico-chimiques, des analyses granulométriques des substrats et des enquêtes. Les résultats montrent des dynamiques d’évolution complexes et contrastées entre progression, stabilité et régression. Au final, en s’appuyant sur les connaissances acquises sur les dynamiques d’évolution des mangroves sur plus de 60 ans, il est possible de mettre à la disposition de tous un outil d’aide à la décision et à la gestion durable et adéquate pour protéger et conserver ces écosystèmes, particulièrement dans le contexte du changement climatique qui va impacter les dynamiques d’évolution naturelles et les forçages anthropiques
Mangroves have many ecological, socio-economic and climate change mitigation values and functions vital for the littoral populations around the world and in Madagascar.This richness induce them intense exploitation, subjecting to strong natural and anthropogenic pressures. However in Madagascar "the mangroves are very poorly understood and we do not have the elements necessary for a good diagnosis", while they are presented as of perpetual regression in the Madagascar Southwest region. This study aims at identifying, mapping and quantifying the evolution (since 1949) of 5 mangrove’s sites in the Southwest : Manombo-Fitsitike, Ambondrolava, Ankiembe, Sarodrano and Andriambe. It also aims the diagnosis of the different factors of evolution putting in perspective the anthropogenic and natural pressures. To achieve these objectives, two approaches were adopted : geomatics based on the diachronic analysis of Spot images from1987, 1998, 2012 and 2014 associated with aerial photographs (1949) and field work with floristic inventories, physico-chemical measurements, particle size analyzes of substrates and surveys. The results show complex and contrasting trend evolution’s dynamics between growth, stability and regression. In the end, based on the knowledge gained on the mangroves dynamic over more than 60 years, it is possible to make available to all a tool to help decision-making and sustainable and adequate management to protect and conserve these ecosystems, particularly in the context of climate change that will impact natural changes and anthropogenic forcing

As dominant ecosystems on protected tropical and subtropical shorelines, mangroves are globally important for essential ecosystem services such as acting as nursery habitat for juvenile nekton, land building and coastal protection. The structural complexity associated with the aerial roots of mangroves strongly underpins these services. However, due to the lack of a satisfactory method for measuring and quantifying this complexity, the relationship between complexity and mangrove ecosystem services is still obscure. The objectives of this study were (1) to find a low-cost method for realistically quantifying habitat complexity; and (2) to assess the importance of habitat structural complexity to the principal ecosystem services offered by mangroves, namely, supporting fish assemblage, flow attenuation and sediment trapping. An innovative, simple, and low-cost method based on an RGB_D scanning sensor (Kinect) and free and readily accessible software (Meshlab, Matlab, Qubicle Constructor and Voxeliser) was used to capture realistic 3D models of mangrove aerial roots. This low-cost approach provides a novel method to capture and measure structural complexity at a mesoscale in a full 3D approach, enabling an analysis of the relationship between habitat complexity and mangrove ecosystem services. The fractal dimension (FD) and AVR (area/volume ratio of the 3D model) indices were developed to quantify mangrove root structural complexity. The cube counting method was used for three-dimensional characterisation of FD of the space around aerial roots. To assess the apparent complexity of the structure to fish potentially using the roots, rectangular prisms with dimensions corresponding to the allometry of the fish were used to estimate the FD values.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
Full Text

OLIVEIRA FILHO, Romildo Lopes de. Dinâmica de fósforo em manguezais impactados por águas residuárias no Estado do Ceará. 2012. 62 f. Dissertação (Mestrado em ecologia e recursos naturais)- Universidade Federal do Ceará, Fortaleza-CE, 2012.
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Recent studies demonstrated the efficacy of mangrove retaining nutrients and, in particular, the ability of the mineral component of the buffer in its high soil phosphorus levels. In general, the mangroves have been considered as important sinks of nutrients due to its high capacity purification of effluents. However, depending on the geochemical conditions exist, these soils can act as a source of phosphorus to other environments and / or coastal waters. Given that the geochemical behavior of phosphorus and its role in eutrophication of water bodies, is best measured by the behavior of its different fractions, this paper aims at a fractionation of the different forms of phosphorus in wetlands impacted by different effluent. The objective of this project is to study three areas in order to assess how activities impacting interfere in the process of nutrient cycling (with special emphasis on the dynamics of phosphorus forms) and, as the marsh supports the stress caused by these activities. Also, if you evaluate the potential for eutrophication of each human activities. Taking into consideration the impact that these environments suffer as a result of separate activities, were established the following areas of study: a marsh impacted by effluents from shrimp, a marsh impacted by effluents, and a control area located in a preserved area that still finds is little affected by human impacts. The samples were determined pH, Eh, salinity, grain size and the total content of C and P. In addition, extraction was performed sequentially phosphorus which allows differentiation of fractions 7: P exchangeable (NaClP), P associated with iron oxides (Fe-P); organic P (AH-P), the bound phosphorus hydroxides Al (Al-P), P associated with compounds of calcium (Ca-P); phosphorus associated refracting matter (P-RES) and unreacted phosphorus (P-NR). The results indicate that the discharge of effluents in mangrove increases the amount of phosphorus in these environments, especially in organic form, the phosphorus bound to carbonate is the major inorganic fraction in these environments.
Estudos recentes demonstram a eficácia do manguezal em reter nutrientes e, em especial, a capacidade dos componentes minerais do seu solo em tamponar elevados teores de fósforo. Em geral, os solos dos manguezais têm sido considerados como importantes sumidouros de nutrientes devido a sua grande capacidade de depuração de efluentes. Entretanto, dependendo das condições geoquímicas existentes, esses solos podem funcionar como fonte de fósforo para outros ambientes e/ou para as águas costeiras. Tendo em vista que o comportamento geoquímico do fósforo, bem como seu papel na eutrofização dos corpos d'água, é melhor avaliado através do comportamento de suas diferentes frações, o presente trabalho visa realizar um fracionamento das diferentes formas de fósforo em manguezais impactados por distintos efluentes. O objetivo da presente dissertação é estudar três áreas a fim de se avaliar como as atividades impactantes interferem no processo de ciclagem de nutrientes (com especial ênfase na dinâmica das formas de fósforo) e, como o manguezal suporta o estresse ocasionado por estas atividades. Além disso, se avaliará o potencial de eutrofização de cada uma das atividades antrópicas. Levando-se em consideração os impactos que esses ambientes sofrem em consequência de distintas atividades, foram estabelecidas as seguintes áreas de estudo: um manguezal impactado por efluentes de carcinicultura; um manguezal impactado por efluentes urbanos; e uma área controle localizada em uma área preservada que ainda encontra-se pouco afetada por impactos antrópicos. Nas amostras foram determinados pH, Eh, salinidade, granulometria e teores totais de C e P. Além disso, foi realizada a extração seqüencial de fósforo que permite a diferenciação de 7 frações: P trocável (NaCl-P); P associado a óxidos de Fe (FeP); P orgânico (AH-P); fósforo ligado a hidróxidos de Al (Al-P); P associado a compostos de cálcio (Ca-P); fósforo associado à matéria orgânica refratária (P-RES) e fósforo não reativo (P-NR). Os resultados obtidos indicam que o descarte de efluentes nos manguezais aumenta a quantidade de fósforo nesses ambientes, principalmente nas formas orgânicas; o fósforo ligado aos compostos de cálcio é a principal fração inorgânica nesses ambientes. Palavras-chave: ciclagem de nutrientes; extração sequencial; carcinicultura; efluente domiciliar.

Les zones côtières du monde entier sont sous fort pression de contamination anthropique comme conséquence de la concentration de la plupart de la population mondiale et des activités économiques le long des côtes et des estuaires. La menace de contaminant sur les écosystèmes rend primordial le développement d'outils capable de détecter les modifications biogéochimiques en vue d'aider dans la prévention, la gestion, et la prédiction de risques dans les études environnementales. Dans ce but, cette thèse étudie la biogéochimie des isotopes du Zinc (Zn) en vue de développer un outil capable de tracer les sources naturelles et anthropiques, d'identifier les processus biogéochimiques et de permettre à la biosurveillance de la contamination par les métaux dans les zones côtières et les mangroves. A cette fin, les compositions isotopiques du Zn ont été déterminées à plusieurs échantillons naturels prélevés dans la baie de Sepetiba (au sud-est du Brésil), un estuaire lagunaire affecté par une côte industrialisée située près de Rio de Janeiro. Cette baie constitue un laboratoire naturel idéal pour valider le système isotopique du Zn. En effet, cette zone héberge des écosystèmes d'intérêt commercial et écologique -estuaire, mangrove, estran- menacés par la contamination d'une ancienne activité de galvanoplastie, et d'autres sources diffuses. Les échantillons collectés comprennent des carottes de sédiments, des sédiments de la superficie des mangroves, des matériaux particulaires en suspension (SPM), des feuilles provenant d'arbres de mangrove, des tissus de mollusques bivalves (huîtres et moules) et des roches. Minéraux de dépôt de Vazante (Brésil) ont été collecté pour representé matière première utilisée par l'industrie de la galvanoplastie. Tout d'abord, un travail initial de laboratoire a établi une méthode exacte et précise pour les déterminations isotopiques Zn en échantillons naturelles par spectrométrie de masse avec plasma couplé par induction et multicollecteur (MC-ICP-MS). Des analyses spatiales et temporelles des compositions isotopiques du Zn des échantillons de sédiments et de roches s'ajustent bien à un modèle de mélange entre trois principales extrémités : i) les matériaux continentaux charriés par les rivières ; ii) les sources marines ; et iii) une source anthropique majeure associée aux anciens déchets de galvanoplastie jetés dans la baie. Les carottes de sédiment collectées dans la vasière ont montré une haute corrélation entre la composition isotopique du Zn et le facteur d'enrichissement du Zn. Ceci suggère : i) une bonne préservation du registre isotopique des sources naturelle et anthropique, ii) l'absence de fractionnement isotopique significatif durant le transport de sédiments ou durant les réactions diagénétiques pos-dépositions dans le système estuarien
Coastal areas worldwide are under strong pressure from anthropogenic contamination, as most of the global population and of economic activities are concentrated along the coasts and estuaries. The threaten of contaminant releasing into these ecosystems makes imperative the development of tools capable of detecting biogeochemical changes in order to help prevention, monitoring and prediction of risks in environmental studies. In this way, this thesis investigates the isotope biogeochemistry of Zinc (Zn) in order to develop a tool capable of tracing natural and anthropogenic sources, identifying biogeochemical processes and enabling the biomonitoring of metal contamination in coastal areas and mangroves. To this end, Zn isotopes compositions were determined in several natural samples collected from Sepetiba bay (southeastern Brazil), an estuarine-lagoon impacted by an industrialized coastal area near Rio de Janeiro. This bay constitutes an ideal natural laboratory for evaluating the Zn isotopic system to environmental issues, since it hosts important ecosystems of commercial and ecological interest - estuaries, mangroves and tidal flats - threaten by the metal contamination resultant of old electroplating activity and other anthropogenic diffuse sources. The collected samples include sediment cores, surface mangrove sediments, suspended particulate matter (SPM), leaves of mangrove's trees, tissues of bivalve mollusks (oysters and mussels) and rocks. Ores from Vazante deposit, Brazil were collected to represent the raw material used in the old electroplating industry. Firstly, an initial laboratory work established a method for accurate and precise determinations of Zn isotope compositions in natural samples by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Spatial and temporal analysis of Zn isotope compositions of sediment and rock samples fits well in a model of mixing between three main end-members: i) continental materials brought via rivers; ii) marine sources; and iii) a major anthropogenic source associated to the old electroplating wastes released into the bay. Sediment cores collected in the mud flat showed high correlation between Zn isotope compositions and Zn enrichment factors, suggesting (i) good preservation of isotopic records of natural and anthropogenic sources and (ii) no significant isotopic fractionation during sediment transport or as a result of diagenetic reactions post-deposition in the estuarine system. The sediment core sampled from a mangrove located in the zone impacted by the old electroplating activity presented levels of Zn up to 4% (dry weight) and preserved the isotopic signatures of electroplating wastes. However, there is evidence that biogeochemical processes triggered by hydrodynamics, bioturbation or rhizosphere processes slightly changed the isotopic signatures in some layers. Calculations based in this mixing model quantified contributions of the major anthropogenic source of Zn, ranging from negligible values in the pre-industrial period to nearly 80% during periods of electroplating activities between the 60's and 90's

Les forêts de mangrove contribuent de manière significative au flux d'énergie, au cycle des nutriments et du carbone dans l'océan côtier, étant un puits pour le CO2 atmosphérique. Les forêts de mangroves sont très productives et stockent une quantité élevée de carbone à la fois dans leurs sols et dans leur biomasse.Au cours de la décomposition de la litière, les nutriments et le carbone peuvent être recyclés ou exportés vers les écosystèmes adjacents par l'action des marées. La mangrove de Can Gio (Ho Chi Minh Ville, Vietnam), dégradée par l'épandage de défoliants pendant la guerre du Vietnam, a pu être restaurée grâce à la replantation et à la régénération naturelle. À ce jour, la forêt de mangrove de Can Gio est la plus grande forêt de mangrove contiguë au Vietnam, et est devenue la première réserve biosphère UNESCO dans ce pays. L'objectif principal de cette thèse était de caractériser le cycle du carbone dans la forêt de mangrove tropicale.Les résultats de cette thèse ont permis de:- Développer des équations allométriques permettant d’estimer la biomasse aérienne de la forêt plantée de mangroves de l’espèceRhizophora apiculatadans le sud du Vietnam;- Calculer les stocks de carbone totaux dans différents peuplements de mangrove se développant sous le climat tropical du sud du Vietnam;- Caractériser les taux de décomposition de la litière et évaluer la dynamique des nutriments et des métaux traces au cours des processus de dégradation de la litière, ainsi que l'évolution de δ13C pendant la décomposition;- Déterminer la variabilité saisonnière des flux de CO2 à différentes interfaces: sol-air, eau-air et tronc-air, et caractériser les profils de concentration en CO2 dans la canopée
Mangrove forests significantly contribute to energy flow, nutrient and carbon cycling in the coastal ocean, being a sink for atmospheric CO2. Mangroves forests are highly productive and store high amount of carbon both in their soils and in their biomass. During leaf litter decomposition, nutrients and carbon can be recycled or exported to adjacent ecosystems by the tidal action. Can Gio mangrove, degraded by the spraying of defoliants during the Vietnam War, successfully recovered through replantation and natural regeneration after 40 years. To date, the Can Gio mangrove forest is the largest contiguous mangrove forest in Vietnam, and became the first Mangrove Biosphere Reserve in this country. The main objective of this PhD thesis was to characterize carbon cycling within the Can Gio mangrove forest, which is a tropical one.The results of this PhD thesis allowed to: - Develop allometric equations and to estimate the aboveground biomass of Rhizophora apiculata Blume planted mangroves forest in Southern Vietnam; - Calculate the total carbon stocks in different mangrove stands developing under the tropical climate of Southern Vietnam; - Characterize the leaf litter decomposition rates, and assess nutrients and trace metals dynamics during litter decay processes, as well as the evolution of δ13C during decay; - Determine the seasonal variability CO2 fluxes at different interfaces: soil-air, water-air and trunk-air, and to characterize CO2 concentrations profiles in the canopy

L'objectif de cette thèse de doctorat consistait à évaluer la production primaire d'une mangrove d'estuaire en Guyane française. Pour répondre à cet objectif, deux approches complémentaires ont été mises en parallèle : l'une a l'échelle locale et l'autre a l'échelle régionale. La première approche abordait des processus internes à la mangrove. A partir de la caractérisation (structure, phytomasse épigée) de la mangrove en cinq stades évolutifs, des dispositifs expérimentaux ont permis de suivre mensuellement les variations spatiales et saisonnières de la chute et de la décomposition des litières et des apports au sol en nutriments. Les résultats sont comparables avec ceux des mangroves se situant aux mêmes latitudes. Les conditions du substrat peuvent expliquer en partie les variations spatiales observées. Les variations saisonnières sont liées aux données climatiques (corrélation significative avec la pluviométrie, l'insolation et le vent). Il semblerait que ce soit l'âge de la population, le mode de croissance des espèces et les conditions de drainage des milieux qui induisent les variations de compositions foliaires en nutriments. La deuxième approche pourrait permettre à terme de spatialiser ces processus à une échelle plus globale. Pour cela, des photographies aériennes à grande échelle, acquises a bord d'un Ulm et à des altitudes variant de 100 à 1500 m, ont été utilisées pour mettre en évidence des relations entre paramètres mesures au sol et des paramètres observables par photo-interprétation.

Mangroves are intertidal ecosystems found along the tropical and subtropical coastlines.

Though globally recognised as ecosystems of ecological, biological and economical

remarkable importance, these ecotone formations are characterised by a continuously

increasing anthropization. However, very little studies have been focused on the impact of

various anthropogenic activities on the mangrove vegetation structure.

We have firstly (a) assessed the commercial and subsistence utilization of mangrove

wood products in the Littoral region (Cameroon estuary). Then, we have confronted the

subsistence usages of mangrove wood products in the Southern region (close to the mouth of

the Nyong River and Mpalla village (Kribi)) in comparison with the Littoral region. By doing,

we have compared the local residents‟ perceptions on environmental changes that occurred

within the two regional mangrove forests. Also, we have (c) studied the structural dynamic of

mangrove vegetation neighbouring the Douala city (Cameroon). Always in the vicinity of this

town, we have (d) reconstructed the original structure of largely disturbed mangrove forests.

Moreover, we have (e) map the mangrove structure in a non peri-urban setting located within

the Cameroon estuary. Here, we have finally (f) analysed the spatial distribution of a black

mangrove namely Avicennia germinans (L.) Stearn.

Our results underlined an excessive utilization of mangrove wood products in the

Cameroon estuary. We have showed that the frequency of mangrove harvesting was relatively

fewer in Kribi (Mpalla) and the mouth of the Nyong River. The local people inhabiting these

two localities perceived mangroves as less degraded areas. In contrast, those established

within the Cameroon estuary stated that mangroves were largely disturbed. When combining

the local people statements with our field observations, we recorded that it a complex mix of

causes (e.i. clear-felled corridors, agriculture, sand and gravel extraction, over-harvesting and

anarchic urbanization) that have led to the largely degradation (vegetation and sediment) of

the peri-urban mangroves in Cameroon. A diachronic analysis (1974, 2003, 2009) of their

coverage revealed that over the 35-year period, mangrove had decreases in cover of 53.16%

around Douala. We have also showed that in the peri-urban settings, wood harvesting was

commonly applied on the structurally more complex (highly dense stands neighbouring the

habitations) mangrove forests (Mboussa Essengue) and, in a lesser extent, on the structurally

more developed mangrove stands (fewer dense stands faraway from Douala). On the other

hand, the mapping analysis of the non peri-urban mangroves (distant from Douala) has

revealed that the structure of these intertidal forests was relatively less impacted. In the

Cameroon estuary, we also showed that A. germinans trees were randomly distributed on

almost one-half of the sampling plots and clumped at some scales on the remaining plots.

Accordingly, this species might play a significant role in the recovery process of artificial

gaps found in the non peri-urban areas.

The multi-disciplinary approach employed in this study has allowed a better

understanding of the direct and indirect impacts of anthropogenic activities on the mangrove

vegetation structure in Cameroon. These results constitute a fundamental data base quite

useful for the multi-temporal monitoring of these littoral ecosystems perpetually disturbed.

The application of similar approach in other mangroves facing high anthropogenic pressures

appears important.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Mangroves in South Africa are prone to anthropogenic pressures such as browsing and trampling by livestock and by natural disturbances such as drought and floods. These mangroves exist at one of the most southerly limits in the world providing a unique opportunity to study recovery and resilience to change. This study used long term data at three South African study sites located in the subtropical (St Lucia Estuary) and warm temperate regions (Nxaxo and Kobonqaba estuaries) to compare mangrove growth rate, population structure and responses to disturbance. The first objective was investigated at St Lucia Estuary where site specific or microhabitat differences were measured to assess the influence of these on mangrove growth and population structure. It was suggested that site - specific variability would ensure mangrove survival and analysis showed that seedlings were present at different sites in different years. There was always some recruitment but often little survival to the next size class. Over time seedling numbers were quite variable and self – thinning of adults was evident. The second objective was to identify the environmental factors influencing population density and growth. Results showed that sediment moisture and salinity influenced seedling and adult density due to fluctuations in estuary water level. Mangrove growth rates for Avicennia marina in terms of height was faster (40 – 75 cm yr-1 ) at Site 1 where conditions were waterlogged and moderately saline and slower (5 – 25 cm yr1 ) in dry and hypersaline conditions at Site 4. Overall mangroves at St Lucia have shown persistence through drought and fluctuations in environmental conditions however resilience may be hindered at sites that are subjected to partially flooding and prolonged waterlogging. The second site was Nxaxo Estuary in the Eastern Cape where cattle exclusion plots (nonbrowsed) and control plots (browsed) were used to assess the recovery of A. marina trees from cattle browsing. Trees in the browsed plots showed no vertical growth while trees in the non-browsed plots grew significantly faster (5.4 ± 0.5 cm yr-1). When cattle were prevented from entering the mangrove area, the trees recovered fairly quickly and within 3 years growth was similar in both the non – browsed (17.9 ± 3.2 cm yr -1) and browsed plots (18 ± 1.6 cm yr -1). Lastly, mangrove recovery was investigated at Kobonqaba Estuary where long-term closure of the mouth to the sea resulted in high water levels, inundation of pneumatophores and die-back of the majority of the mangroves. This study measured the recovery of the mangroves by assessing changes in vegetation cover and sediment characteristics along transects. High initial porewater nutrient concentrations promoted salt marsh growth and plants increased average cover from 0% in 2011 to 18.9% (2013) and 50% in 2015. The total number of A. marina individuals increased from only seven to 27 individuals over four years. Salt marsh competition and facilitation will likely influence mangrove recovery in the future. Overall it was concluded that when a short term pressure (cattle browsing) is alleviated, mangrove forests even at warm temperate sites are able to recovery rapidly by increasing growth and seedling establishment. However, mangroves in the subtropical sites show more resilience and recovery potential to long term pressures such as fluctuating environmental conditions because of faster growth rates.

For the first time in the history of mangroves, the Ganges-Brahmaputra delta in particular, this doctoral research aims to quantify forest change with an unprecedented period spanning from 1906 to 2014. The world’s largest mangroves – the Sundarbans of the Ganges-Brahmaputra delta accounts for 4.5% of the world’s mangrove forests, has been used as the test site. The research quantified the forest change into two distinct strands: (a) an assessment of vegetation dynamics over 106-years (1906-2012) in the Bangladesh Sundarbans and (b) a 42-years long (1973-2014) satellite imagery-based assessment of spatial change patterns of the Sundarbans. To address those objectives, this study used three different datasets: (1) a three month long extensive ground survey in 2011-12; (2) synthesis of six epochs of vegetation estimates: 1906-10, 1923-26, 1957-59, 1982-84, 1996-97 and 2011-12; and (3) mapping forest and forest types from six epochs of Landsat time-series: 1973 (MSS1), 1979 (MSS3), 1989 (ETM+ 7), 2010 (TM5), and 2014 (OLI8) using ground-based training samples and high (5m-RapidEye) to very high (<5m-GeoEye, IKONOS, QuickBird, OrbView) spatial resolution optical imagery spanning from 1967 to 2014. Ground survey of 164 sample plots, 400 m2 per plot, has recorded 21 tree species from 33 recorded plant species having median values of stem diameter and total height estimated to 3 cm and 5.4 m, respectively. Out of 47,293 stems, gewa was found dominating (42%) which together with sundri constitute about 80% of the stems. Sundri stems were found to be taller than gewa but opposite in the case of stem median diameter and are significant in both cases. Stocking has declined to 50 stems.ha-1 from 650 stems.ha-1 from ≥20 cm to ≥10 cm diameter. Tree richness, diameter and total height has found declining with increasing salinity. The southeast region of the Bangladesh Sundarbans has recorded the highest diameter and taller stems. Overall, total height of stems has declined while tree mortality from top-dying has increased 4.5 times. Over the last 106-years (1906-2012), a 58% decline of ≥15 cm diameter sundri has been estimated. From 1923-2012, the sundri-dominated forest has declined by 34% while gewa and other-dominated forests have increased by 11% and 24% respectively. Decline in larger diameter stems (≥ 5cm) has provided space for younger stems to grow and dominate which showed an overall increase in stocking of sundri, gewa and other-dominated forest types. These long-term forest change estimates will benefit in understanding ecology and carbon dynamics of mangroves that eventually contribute in UN-led reduced emission from deforestation and forest degradation (REDD+) programmes for mangroves of the Ganges-Brahmaputra delta.

L'objectif de ce travail est double: d'une part, trouver des methodes d'inventaire des mangroves et etudier les problemes biologiques de leur developpement, d'autre part, etablir une carte aussi automatique que possible de l'ecosysteme mangrove. Inventaire et cartographie ont ete realises en laboratoire en france et en indonesie. La methode retenue a necessite la prise en compte de travaux de terrain detailles, permettant de bien connaitre la mangrove de java et la validation des resultats. Notre travail comprend les trois etapes suivantes: etablissement d'une carte thematique preliminaire, saisie des donnees de terrain et etablissement d'une carte thematique definitive. Donnees de terrain et donnees satellitaires ont ete utilisees pour l'etablissement d'une synthese et pour etablir la carte definitive couvrant les deux regions javanaises: cilacap (cote sud de java) et surabaya (cote nord de java). Les resultats permettent d'estimer le devenir de cette mangrove, de poser les bases d'un bon amenagement de ces ressources naturelles avec une bonne connaissance de leur evolution. Ce travail s'inscrit donc dans une perspective scientifique portant sur une meilleure utilisation de la teledetection spatiale. Il a ete realise dans le cadre du developpement du centre de cartographie et teledetection de l'institut technologique sepuluh november a surabaya, indonesie