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1
Kim, Hey-Jin. "Climate impacts on the planktonic marine ecosystem in the Southern California current." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2008. http://wwwlib.umi.com/cr/ucsd/fullcit?p3307584.
Texte intégralRésumé :
Thesis (Ph. D.)--University of California, San Diego, 2008.<br>Title from first page of PDF file (viewed July 18, 2008). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
2
Sakai, Yoichiro. "Spatio-temporal dynamics of planktonic food webs in the coastal ecosystem of Lake Biwa." 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/180371.
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Drexel, Jan Peter. "Contribution of Nitrogen Fixation to Planktonic Food Webs North of Australia." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/19733.
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Nitrogen fixation is no longer considered to be a minor factor of the nitrogen cycle in oceanic ecosystems. Recent geochemical and biological efforts have led to a significant increase in the estimated input of nitrogen to marine ecosystems by biological fixation, while molecular studies have increased our knowledge of the number and diversity of nitrogen fixers known to be active in the ocean. Although Trichodesmium spp. have long been viewed as the primary marine nitrogen fixers, recent efforts have shown that various members of the picoplankton community are also actively involved in nitrogen fixation. The relative abundance of different nitrogen fixers is an important ecosystem parameter since nitrogen fixers may differ significantly in their physiology, life history and ecology. Here we combine rate measurements and stable isotope natural abundance measurements to constrain the impact of N2 fixation in the waters north of Australia. Samples were collected in the Coral, Arafura, and East Timor Seas, thus spanning three distinct hydrographic regions. Our data show that Trichodesmium has a significant influence on the stable nitrogen isotope ratios of particulate and zooplankton biomass and suggest that Trichodesmium is a significant source of nitrogen for the pelagic ecosystem. Based on stable carbon isotope ratios, it is also likely that the pathways are indirect and nitrogen fixed by Trichodesmium enters the higher trophic levels via decomposition as dissolved organic and inorganic nitrogen. Picocyanobacteria showed high diazotrophic activity at some stations, but unlike Trichodesmium, their N2 fixation rate was not reflected in the stable N isotope ratios of particulate and zooplankton biomass. Our results suggest an important N contribution to biomass by diazotrophs in the Coral Sea, Arafura Sea and East Timor Sea.
4
Chabert, Pierre. "Impact of Synoptic Wind Variability on the Dynamics and Planktonic Ecosystem of the South Senegalese Upwelling Sector." Electronic Thesis or Diss., Sorbonne université, 2023. http://www.theses.fr/2023SORUS096.
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En plus du cycle saisonnier du vent, les systèmes d'upwelling de bord Est des océans subissent des fluctuations à des échelles de temps plus courtes, intrasaisonnières ou synoptiques. Dans cette thèse, nous nous concentrons sur l'impact d'une intensification ou d'une relaxation du vent synoptique sur une période de 5 à 10 jours sur la dynamique et l'écosystème planctonique du secteur d'upwelling du sud Sénégal (SSUS). Ce système possède un plateau continental particulièrement peu profond et est situé au sud de l'abrupte péninsule du Cap-Vert, qui casse la continuité de la ligne de côte. Notre objectif est d'apporter des connaissances supplémentaires sur ce système d'upwelling côtier qui, malgré son importance, a reçu peu d'attention, en particulier aux échelles de temps synoptiques. Pour étudier cela, nous développons une expérience de modélisation qui consiste à appliquer une intensification et une relaxation idéalisées du vent synoptique à un ensemble d'états climatologiques du SSUS. Les fluctuations synoptiques ont un impact sur toutes les variables dynamiques et façonnent des anomalies robustes des structures spatiales à l'échelle du système et à la méso-échelle. En appliquant un bilan de chaleur de la couche mélangée, nous identifions l'importance des processus horizontaux et l'importance très localisée des processus verticaux dans la variabilité du SSUS. Aussi, nous constatons que les biomasses planctoniques oscillent dans l'espace et le temps en réponse aux fluctuations synoptiques. La perturbation atmosphérique est amortie lors de sa propagation vers les niveaux trophiques supérieurs de l'écosystème. La réponse de l'écosystème planctonique est complexe et hétérogène sur le plateau, avec un comportement distinct sur le plateau interne. Un bilan des diatomées révèle que leur biomasse est principalement contrôlée par la production primaire, le broutage du zooplancton et la mortalité-agrégation. L'équilibre entre ces processus est responsable des réponses oscillatoires de la biomasse des diatomées aux événements synoptiques. Toutes les variables dynamiques et biogéochimiques présentent de modestes asymétries entre les réponses d'intensification et de relaxation du vent. Cela supporte l'hypothèse selon laquelle la variabilité synoptique a un impact seulement modeste sur l'état moyen climatologique. Les implications de nos résultats pour les futures questions de recherche sont discutées, notamment l'importance des observations biogéochimiques et les avancées de la modélisation des écosystèmes planctoniques<br>In addition to the wind seasonal cycle, Eastern Boundary Upwelling Systems undergo fluctuations at shorter synoptic to intraseasonal time scales. This thesis focuses on the impact of synoptic wind intensifications and relaxations with a period of 5-10 days on the dynamics and planktonic ecosystem of the South Senegalese Upwelling Sector (SSUS). This system is located south of the sharp Cape Verde peninsula which acts as an abrupt coastline break and has a particularly shallow continental shelf. We aim to bring additional knowledge on this important coastal upwelling system that has received little attention, especially at synoptic time scales. To investigate this, we develop a modeling framework that involves applying idealized synoptic wind intensification and relaxation to an ensemble of climatological SSUS states. Synoptic fluctuations impact all dynamical variables out of their intrinsic variability range and shape robust anomalies of SSUS-scale and mesoscale spatial patterns. Using a mixed layer heat bud- get over the shelf, we identify the importance of horizontal processes in the SSUS heat variability and the very localized importance of vertical processes. Plankton biomass are found to oscillate in space and time in response to synoptic wind fluctuations. The atmospheric perturbation is damped during its propagation towards the upper trophic levels of the ecosystem. The response of the planktonic ecosystem is complex and heterogeneous over the shelf, with a distinctive inner shelf behavior. A diatoms budget reveals that their biomass is primarily controlled by primary production, zooplankton grazing and mortality-aggregation. The balance between these processes is responsible for the oscillatory responses of the diatoms biomass to synoptic wind events. All dynamical and biogeochemical variables exhibit modest asymmetries between wind intensification and relaxation responses. This brings support to the hypothesis that synoptic variability has a modest net impact on the climatological mean state. The implications of our results for future research questions are discussed, including the importance of biogeochemical observations and advances in plankton ecosystem modeling
5
Rykaczewski, Ryan Ross. "Influence of oceanographic variability on the planktonic prey and growth of sardine and anchovy in the California current ecosystem." Diss., [La Jolla] : University of California, San Diego, 2009. http://wwwlib.umi.com/cr/ucsd/fullcit?p3354961.
Texte intégralRésumé :
Thesis (Ph. D.)--University of California, San Diego, 2009.<br>Title from first page of PDF file (viewed June 16, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
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Kretschmer, Kerstin [Verfasser], Michael [Akademischer Betreuer] Schulz, Michael [Gutachter] Schulz, and Gerold [Gutachter] Wefer. "Global assessment of species-specific habitats of planktonic foraminifera : an ecosystem modeling approach / Kerstin Kretschmer ; Gutachter: Michael Schulz, Gerold Wefer ; Betreuer: Michael Schulz." Bremen : Staats- und Universitätsbibliothek Bremen, 2017. http://d-nb.info/1153119374/34.
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Aquino, Camila Akemy Nabeshima. "A distribuição funcional do fitoplâncton prediz a variabilidade ambiental entre dois rios subtropicais." Universidade Estadual do Oeste do Paraná, 2017. http://tede.unioeste.br/handle/tede/3482.
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Previous issue date: 2017-03-31<br>Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Estado do Paraná (FA)<br>Phytoplankton traits diversity provides a powerful means to addressing ecology’s questions, and can be 43 adopted to simplify and predict the community structure, in function of the multiples environmental filters 44 that operate in the different ecosystems. Thus, we evaluated the response of phytoplankton functional 45 groups of two subtropical rivers in a temporal scale, identifying the main environmental filters associated 46 with the presence of the different groups and their functional traits during a seasonal cycle. Using 47 multivariate analysis, we found an environmental dissimilarity predicted by the presence of different 48 functional groups in the rivers. Six GFs were recorded: J (chlorophyceans chlorococcales), M (colonial 49 cyanobacteria), N (desmids), W1 (euglenophyceans), X2 (flagellated unicellular chlorophyceans) and F 50 (flagellated colonial chlorophyceans). The GFs J, M and N were exclusive to the first river, while X2 and 51 F were exclusive to the second river. GF W1 was recorded in both rivers, however, its greatest 52 contribution occurred to the second river. Thus, the GFs reflected the environmental dissimilarity, mainly 53 related to the conditions of water flux, conductivity, light availability and depth of the environments. In 54 view of the obtained results, the functional grouping considered a relevant tool in phytoplankton ecology, 55 offers a practical means to investigating the relation between phytoplankton and ecosystem functioning, 56 and consequently can assist in decision-making for the management and conservation of the biodiversity 57 in lotic environments<br>A diversidade dos traços fitoplanctônicos fornece um poderoso recurso para abordar as questões da 13 ecologia e pode ser adotada para simplificar e prever a estrutura da comunidade, em função dos múltiplos 14 filtros ambientais que operam nos diferentes ecossistemas. Assim, avaliamos a resposta dos grupos 15 funcionais fitoplanctônicos de dois rios subtropicais em escala temporal, identificando os principais filtros 16 ambientais associados à presença dos diferentes grupos e seus traços funcionais durante um ciclo sazonal. 17 Com a análise multivariada, encontramos uma dissimilaridade ambiental prevista pela presença de 18 diferentes grupos funcionais nos rios. Foram registrados seis GFs: J (clorofíceas clorococcales), M 19 (cianobactérias coloniais), N (desmídias), W1 (euglenofíceas), X2 (clorofíceas unicelulares flageladas) e 20 F (clorofíceas coloniais flageladas). Os GFs J, M e N eram exclusivos do primeiro rio, enquanto X2 e F 21 eram exclusivos do segundo rio. GF W1 foi registrado em ambos os rios, no entanto, a maior contribuição 22 ocorreu no segundo rio. Assim, os GFs refletiram a dissimilaridade ambiental, principalmente relacionada 23 às condições de fluxo de água, condutividade, disponibilidade de luz e profundidade dos ambientes. Em 24 vista dos resultados obtidos, o agrupamento funcional considerado uma ferramenta relevante na ecologia 25 do fitoplâncton, oferece um meio prático para investigar a relação entre o fitoplâncton e o funcionamento 26 do ecossistema e consequentemente pode auxiliar na tomada de decisões para a gestão e conservação da 27 biodiversidade em ambientes lótico
8
Haupt, Florian. "Plankton vertical migrations - Implications for the pelagic ecosystem." Diss., lmu, 2011. http://nbn-resolving.de/urn:nbn:de:bvb:19-135130.
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Yool, Andrew. "The dynamics of open-ocean plankton ecosystem models." Thesis, University of Warwick, 1997. http://wrap.warwick.ac.uk/1129/.
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Leach, Taylor Hepburn. "Cause and Consequences of Spatial Dynamics of Planktonic Organisms in Lake Ecosystems." Miami University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=miami1479747973843758.
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Wallhead, Philip John. "Accounting for unpredictable spatial variability in plankton ecosystem models." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/63762/.
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Limitations on our ability to predict fine-scale spatial variability in plankton ecosystems can seriously compromise our ability to predict coarse-scale behaviour. Spatial variability which is deterministically unpredictable may distort parameter estimates when the ecosystem model is fitted to (or assimilates) ocean data, may compromise model validation, and may produce mean-field ecosystem behaviour discrepant with that predicted by the model. New statistical methods are investigated to mitigate these effects and thus improve understanding and prediction of coarse-scale behaviour e.g. in response to climate change. First, the standard model fitting technique is generalised to allow model-data ‘phase errors’ in the form of time lags, as has been observed to approximate mesoscale plankton variability in the open ocean. The resulting ‘variable lag fit’ is shown to enable ‘Lagrangian’ parameter recovery with artificial ecosystem data. A second approach employs spatiotemporal averaging, fitting a ‘weak prior’ box model to suitably-averaged data from Georges Bank (as an example), allowing liberal biological parameter adjustments to account for mean effects of unresolved variability. A novel skill assessment technique is used to show that the extrapolative skill of the box model fails to improve on a strictly empirical model. Third, plankton models where horizontal variability is resolved ‘implicitly’ are investigated as an alternative to coarse or higher explicit resolution. A simple simulation study suggests that the mean effects of fine-scale variability on coarse-scale plankton dynamics can be serious, and that ‘spatial moment closure’ and similar statistical modelling techniques may be profitably applied to account for them.
12
Liu, Cheng-Chien. "Using SeaWiFS ocean colour data to test a plankton ecosystem model." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.343733.
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Lange, Michael. "Embedding individual-based plankton ecosystem models in a finite element ocean model." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/18051.
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Computational models of the ocean plankton ecosystem are traditionally based on simulating entire populations of microbes using sets of coupled differential equations. However, due to recent advances in high-performance computing, a new class of individual-based models (IBM) has come to the fore, which uses computational agents to model individual sub-populations of marine plankton. Although computationally more expensive, these agent-based models offer features that cannot be re-created using population-level dynamics, such as individual life cycles, intra-population variability and an increased stability over parameter ranges. The main focus of this thesis is the implementation and verification of an embedded modelling framework for creating agent-based plankton ecology models in Fluidity-ICOM, a state-of-the-art ocean model that solves the Navier-Stokes equations on adaptive unstructured finite element meshes. Since Fluidity-ICOM provides an interface for creating population-based ecology models, a generic agent-based framework not only enables the integration of existing plankton IBMs with adaptive remeshing technology, but also allows individual and population-based components to be used within a single hybrid ecosystem. This thesis gives a full account of the implementation of such a framework, focusing in particular on the movement and tracking of agents in an unstructured finite element mesh and the coupling mechanism used to facilitate agent-mesh and agent-agent interactions. The correctness of the framework is verified using an existing agent-based ecosystem model with four trophic levels, which is shown to settle on a stationary annual attractor given a stable cycle of annual forcing. A regular cycle of phytoplankton primary production and zooplankton reproduction is achieved using a purely agent-based implementation and a hybrid food chain version of the model, where the two top-level components of the ecosystem are modelled using Eulerian field equations. Finally, a standalone phytoplankton model is used to investigate the effects of vertical mesh adaptivity on the ecosystem in a three-dimensional mesh.
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Spall, Steven Andrew. "The impact of mesoscale jet activity on plankton heterogeneity and primary production : a numerical modelling study." Thesis, University of Southampton, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243174.
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Penczykowski, Rachel M. "Interactions between ecosystems and disease in the plankton of freshwater lakes." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50368.
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I investigated effects of environmental change on disease, and effects of disease on ecosystems, using a freshwater zooplankton host and its fungal parasite. This research involved lake surveys, manipulative experiments, and mathematical models. My results indicate that ecosystem characteristics such as habitat structure, nutrient availability, and quality of a host’s resources (here, phytoplankton) can affect the spread of disease. For example, a survey of epidemics in lakes revealed direct and indirect links between habitat structure and epidemic size, where indirect connections were mediated by non-host species. Then, in a mesocosm experiment in a lake, manipulations of habitat structure and nutrient availability interactively affected the spread of disease, and nutrient enrichment increased densities of infected hosts. In a separate laboratory experiment, poor quality resources were shown to decrease parasite transmission rate by altering host foraging behavior. My experimental results also suggest that disease can affect ecosystems through effects on host densities and host traits. In the mesocosm experiment, the parasite indirectly increased abundance of algal resources by decreasing densities of the zooplankton host. Disease in the experimental zooplankton populations also impacted nutrient stoichiometry of algae, which could entail a parasite-mediated shift in food quality for grazers such as the host. Additionally, I showed that infection dramatically reduces host feeding rate, and used a dynamic epidemiological model to illustrate how this parasite-mediated trait change could affect densities of resources and hosts, as well as the spread of disease. I discuss the implications of these ecosystem–disease interactions in light of ongoing changes to habitat and nutrient regimes in freshwater ecosystems.
16
Perriss, Stephen James. "The physiological ecology of photosynthetic ciliated protozoa and their trophic roles in freshwater and brackish planktonic microbial food webs." Thesis, Lancaster University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.334069.
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Blight, Stephen Paul. "Microbial metabolism and temperature : comparative studies in the Southern Ocean and a temperate coastal ecosystem." Thesis, Bangor University, 1996. https://research.bangor.ac.uk/portal/en/theses/microbial-metabolism-and-temperature--comparative-studies-in-the-southern-ocean-and-a-temperate-coastal-ecosystem(b794f8c8-258d-41cf-847d-b355e2091a96).html.
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Bacterial abundances and production, and the size distribution of oxygen metabolism and chlorophyll a concentration were followed through two seasonal cycles in the Menai Strait (North Wales, U. K. ) and during austral summer in the Southern Ocean. In the Menai Strait, spring blooms were characterised by a diatom to Phaeocystis succession. In both the Menai Strait and the Southern Ocean, meso- and microphytoplankton dominated phytoplankton production and biomass during diatom blooms. Nanophytoplankton predominated when production and biomass were low, i. e. during the summer in the Menai Strait, in waters near the Polar Front, and in some samples from the Weddell Sea. In both ecosystems substantial respiration resided in the bacterial (< 0.8 gm) size-fraction. Consequently during the Menai Strait temporal study, phasing of respiration in relation to photosynthesis was strongly influenced by bacterial metabolism and abundance changes. The respiration maximum occurred 1-2 weeks after the Phaeocystis abundance maximum. An explanation for this temporal lag was sought by considering the time scales of flow of organic material between the phytoplankton and the bacteria. The observations were consistent with routes via a slowly cycling pool, such as polymeric organic material. This pool would function as a reservoir and result in microheterotrophic respiration persisting after the decline of photosynthesis, causing a positive to negative temporal sequence in net community production. There was no evidence for differences in any measure of microbial biomass between the Southern Ocean and the Menai Strait. General relationships could be derived for both ecosystems: (a) the biomass quotient (< 20 µm phytoplankton / unfractionated phytoplankton) generally increased sharply as unfractionated phytoplankton biomass decreased, (b) bacterial biomass generally increased as phytoplankton biomass increased, (c) the biomass quotient of bacteria to unfractionated phytoplankton increased sharply as unfractionated phytoplankton biomass decreased. Different relationships were derived for the oxygen fluxes in terms of phytoplankton biomass for the Southern Ocean and Menai Strait observations. In these relationships, the oxygen fluxes were generally relatively (relative to the explanatory variable: phytoplankton biomass) higher in the Menai Strait. In contrast, a single relationship for DCR in terms of GCP was fitted for both data sets. This difference is consistent with a temperature effect on the oxygen fluxes, with GCP and DCR similarly suppressed at lower temperatures.
18
Haupt, Florian [Verfasser], and Herwig [Akademischer Betreuer] Stibor. "Plankton vertical migrations - Implications for the pelagic ecosystem / Florian Haupt. Betreuer: Herwig Stibor." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2011. http://d-nb.info/1015925219/34.
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Hull, Pincelli Marie. "Macroevolutionary patterns in planktonic foraminifera and the recovery of Pelagic Ecosystems from the Cretaceous-Paleogene mass extinction." Diss., [La Jolla] : University of California, San Diego, 2010. http://wwwlib.umi.com/cr/ucsd/fullcit?p3398253.
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Thesis (Ph. D.)--University of California, San Diego, 2010.<br>Title from first page of PDF file (viewed May 6, 2010). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.
20
Thompson, Patrick Lyn. "Regional plankton diversity as a buffer against environmental change in freshwater ecosystems." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/17411.
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Many experiments show that species diversity at small, local scales affects ecosystems;
however, conservation is concerned with extinctions of species across broad
landscapes. The relevance of global or regional diversity to ecosystems therefore
remains in question. I asked whether regional biodiversity in freshwater zooplankton
affects the resilience and resistance of local ecosystems to the multiple stressors of
warming and salinization. I hypothesised that dispersal of species from the regional
community should buffer ecosystems against environmental change by providing
species with traits adapted to the novel conditions. I subjected freshwater zooplankton
communities in mesocosms that were either connected to or isolated from the larger
regional species pool to a factorial manipulation of experimental warming and increased
salinity. Dispersal introduced heat-tolerant regional taxa that were able to compensate
for reductions in local taxa under warmed conditions. Dispersal also dampened the
effects of warming on net primary productivity, suggesting that regional diversity can
provide stability against some aspects of climate change. However, other measures of
ecosystem performance like decomposition and sedimentation were affected by
warming and salinity but not dispersal. The results indicate that regional biodiversity
provides important insurance that can stabilize ecosystems in a dynamic environment.
However, compensation by the regional biota could not buffer all ecosystem rates
against all sources of stress. My results show that the connectivity of habitats to
regional biodiversity introduces species with broad ranges of traits that can maintain
some local ecosystem function in the face of environmental changes.
21
Briland, Ruth. "Evaluating the causes and consequences of ecosystem change in Lake Erie: From plankton to fish." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu1532076326598788.
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Behl, Stephan [Verfasser], and Herwig [Akademischer Betreuer] Stibor. "Diversity effects on ecosystem processes : a mechanistic approach using plankton communities / Stephan Behl. Betreuer: Herwig Stibor." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2012. http://d-nb.info/1025821971/34.
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Sales, Claudiana Paula de Souza. "Diversidade de bactérias quitinolíticas isoladas em amostras de água do mar e plâncton coletadas na região costeira do estado de São Paulo." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/87/87131/tde-21122009-111113/.
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Bactérias quitinolíticas são autóctones do ecossistema marinho e tem um importante papel no processo de degradação de quitina. Relativamente pouco é conhecido sobre a diversidade e potencial enzimático de bactérias quitinolíticas isoladas de ambientes tropicais costeiros. Amostras de água do mar e de plâncton foram coletadas no Canal de São Sebastião, Baixada Santista e Ubatuba. As bactérias quitinolíticas foram enumeradas e isoladas em meio mínimo contendo quitina coloidal e caracterizadas através de métodos fenotípicos e genotípicos. As maiores contagens de bactérias quitinolíticas foram observadas em amostras de água do mar e plâncton coletadas na Baixada Santista. A diversidade de bactérias quitinolíticas e o potencial de produção de quitinases foram influenciados pelo nível de contaminação fecal presente no ecossistema marinho. Uma maior diversidade foi encontrada em ambiente com médio e baixo impacto antropogênico, mas bactérias quitinolíticas isoladas de ambiente com alta atividade antropogênica mostraram os maiores valores de produção de quitinases.<br>Chitinolytic bacteria are autochthonous in marine ecosystems and have an important role in chitin degradation process. A very little is know about the diversity and enzymatic potential of chitinolytic bacteria isolated from coastal tropical environments. Seawater and plankton samples were collected at Canal de São Sebastião, Baixada Santista and Ubatuba. Chitinolytic bacteria were counted and isolated in minimal media containing colloidal chitin and characterized using phenotypic and genotypic methods. Highest counts of chitinolytic bacteria were observed in seawater and plankton samples collected at Baixada Santista. The diversity of chitinolytic bacteria and the potential of chitinases production were influenced by the level of fecal contamination present in the marine ecosystem. Highest diversity was found in environment with medium and low anthropogenic impact, but chitinolytic bacteria isolated from environment with high anthropogenic influences showed highest chitinases production.
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Sachse, René. "Influence of climate change on lake ecosystems - disentangling physical, chemical and biological interactions." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-167312.
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Climate change affects lake ecosystems in many ways by direct and indirect temperature impacts on hydrophysical structure, hydrology, chemical cycles and on biological interactions. The identification of these climate signals can be complicated and superimposed by other environmental changes, such as land use changes. The aim of this thesis was to seperate temperature effects from effects of management and other environmental influences and to understand the underlying complex processes causing significant changes of ecosystem states. This understanding is important for decisions of lake and reservoir managers to counteract unfavorable consequences of climate change. For the recent study, long-term data of meteorological, hydrophysical and biological variables (phytoplankton, crustacean zooplankton, fish) of the German drinking water reservoir Saidenbach were analysed. Based on this long-term data set, strong indicators for climate induced changes have been identified. In particular, increasing water temperatures since 1975, earlier break up of ice covers and an altered hydrophysical structure could be detected. Thereby, stratification stability increased and turbulent mixing decreased in summer. The water of the reservoir warmed more than the tributaries resulting in a trend to deeper entrainment of the inflows. As further indicators of climate change, an increased annual biomass of phytoplankton and species shifts in the phytoplankton community in spring and summer had been observed. During the spring mass development, the diatom Aulacoseira subarctica became dominant in recent years with warm winters and early ice-out. Its unusual spatial pattern with occurrences in aphotic depths could be explained by easier resuspension compared to other diatoms. By being resuspended first and establishing a high inoculum, A. subarctica profits from an earlier ice-out and earlier full circulation. In spite of a reduced nutrient loading to the epilimnion, in summer, the diatom Fragilaria crotonensis was displaced increasingly by cyanobacteria. This species shift could be explained well by the hydrophysical regime shift. Although, the annual total phytoplankton biomass increased since 1990, the crustacean zooplankton in Saidenbach reservoir did not seem to profit from improved food resources. To the contrary, Daphnia abundances reduced tremendously. We could show that the influcence of fish stocks were underestimated. The stocked silvercarp may have contributed up to 70 % of the total zooplanktivorous fish biomass which had a temperature and density dependent effect. The faster growth of Daphnia at higher temperatures could not compensate for the more actively grazing fish when stock of zooplankitvorous fish was too high. Still, temperature was identified as the most important factor that explained 29 % of the zooplankton phenology, while the second most important predictors were zooplanktivorous fish biomass and nutrient loading, explaining 18 % of the variance. The importance of submerged macrophytes in shallow lakes is well investigated. To increase also the understanding of their impact and their role during climate change on water quality in deep lakes, a model for stratified lakes that includes submerged macrophytes was developed. The simulations showed that macrophyte effects were mainly positive for water quality and macrophytes in deep lakes were able to potentially reduce summer phytoplankton, especially cyanobacteria by 50 % in 11 m deep and still by 15 % in 100 m deep oligotrophic lakes. Nutrient competition with phytoplankton contributed most to this macrophyte effect. In conclusion, for deep lake restoration the re-establishment of submerged macrophytes might be as important as for shallow lakes. The full lake model includes hydrophysical and ecological submodules and thus will allow further comprehensive climate simulations and the evaluation of the effectivity of adaptive strategies and scenarios for deep lakes and reservoirs<br>Der Klimawandel beeinflusst Seeökosysteme vielfältig durch direkte und indirekte Temperatureffekte auf die hydrophysikalische Struktur, die Hydrologie, chemische Kreisläufe und biologische Interaktionen. Die Identifikation von Klimasignalen kann durch Landnutzungs- und weitere Umweltveränderungen überlagert werden. Ziel dieser Arbeit war es, Temperatureffekte von Effekten zu unterscheiden, die durch Gewässermanagement oder anderen Umweltveränderungen verursacht werden. Weiterhin sollten komplexe Prozesse verstanden werden, die zu signifikanten Veränderungen in Seeökosystemen führen. Dieses Verständnis ist für Talsperren- und Gewässermanager von besonderer Bedeutung, um ungewünschten Folgen des Klimawandels entgegenwirken zu können. Für die Studie wurden Langzeitdaten für meteorologische, hydrophysikalische und biologische Variablen (Phytoplankton, Crustaceen-Zooplankton, Fischbesatz) der Talsperre Saidenbach ausgewertet. Mehrere Indikatoren für die Auswirkungen des Klimawandels konnten basierend auf diesen Daten identifiziert werden. Diese gehören insbesondere eine Erhöhung der Wassertemperatur seit 1975, zeitigere Eisaufbrüche und eine veränderte Schichtungsstruktur. Dabei wurde im Sommer die Schichtungsstabilität höher und die Intensität der Durchmischung geringer. Das Wasser in der Talsperre erwärmte sich stärker als die Zuflüsse, wodurch diese sich zunehmend tiefer und unterhalb der Thermokline einschichten. Eine zunehmende jährliche Phytoplanktonbiomasse und Artenwechsel innerhalb der Planktongemeinschaft sind weitere Indikatoren für Klimafolgen. Die Kieselalge Aulacoseira subarctica erlangte in Jahren mit warmen Wintern und zeitigen Eisaufbrüchen eine Dominanz während der Frühjahrsentwicklung. Das ungewöhnliche Auftreten dieser Art in aphotischen Tiefen konnte durch eine leichtere Resuspension im Vergleich zu anderen Kieselalgen erklärt werden. Durch zeitige Resuspension gleich nach Eisaufbruch kann A. subarctica ein hohes Inokulum etablieren. Trotz reduzierter Nährstoffzufuhr ins Epilimnion wurde im Sommer die Kieselalge Fragilaria crotonensis vermehrt durch Cyanobakterien verdrängt, was jedoch gut mit den Änderungen der hydrophysikalischen Struktur erklärt werden kann. Obwohl seit 1990 insgesamt mehr Phytoplankton zur Verfügung steht konnte das Crustaceen- Zooplankton in der Talsperre Saidenbach nicht von diesen verbesserten Nahrungsbedingungen profitieren. Die Daphnia-Abundanzen waren seit 1990 stark verringert. Es konnte gezeigt werden, dass der Einfluss des Fischbesatzes unterschätzt wurde und die künstlich ins System eingebrachten Silberkarpfen zeitweise bis zu 70% der zooplanktivoren Fischbiomasse ausgemacht haben. Zoo- planktivore Fische haben einen temperatur- und dichteabhängigen Effekt auf das Zooplankton. Das schnellere Populationswachstum von Daphnia kann bei hohem Besatz mit zooplanktivoren Fischen nicht die erhöhte Fraßaktivität der Fische ausgleichen. Dennoch konnte Temperatur als der wichtigste Einflussfaktor auf die Phänologie des Zooplanktons identifiziert werden, gefolgt von zooplanktivorem Fisch und Nährstoffzufuhr. Die Wichtigkeit von submersen Makrophyten in Flachseen ist gut untersucht. Um den Einfluss von Makropyhten auf die Wasserqualität während des Klimawandels auch in tiefen Seen abschätzen zu können, wurde ein komplexes Seemodell entwickelt. Die Simulationen zeigen, dass sich Makrophyten hauptsächlich positiv auf die Wassergüte auswirken und zur Reduktion von Phytoplankton, insbesondere von Cyanobakterien im Sommer, beitragen. In einem 11 m tiefen See betrug die Reduktion 50 %, in 100 m tiefen oligotrophen Seen immer noch 15 %. Die Konkurrenz um Nährstoffe mit dem Phytoplankton war dabei die ursächliche Makrophyten-Plankton-Interaktion. Submerse Makrophyten könnten für die Restaurierung von tiefen Seen folglich genauso wichtig sein, wie für Flachseen. Das komplette Seemodell enthält hydrophysikalische und ökologische Module und ermöglicht damit weitere umfassende Simulationen zur Untersuchung der Auswirkungen des Klimawandels und zur Evaluation von Adaptionsstrategien für Seen und Talsperren
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Rohr, Tyler W. "Computational analysis of the biophysical controls on Southern Ocean phytoplankton ecosystem dynamics." Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/122325.
Texte intégralRésumé :
Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2019<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references (pages 193-220).<br>Southern Ocean net community productivity plays an out sized role in regulating global biogeochemical cycling and climate dynamics. The structure of spatial-temporal variability in phytoplankton ecosystem dynamics is largely governed by physical processes but a variety of competing pathways complicate our understanding of how exactly they drive net population growth. Here, I leverage two coupled, 3-dimensional, global, numerical simulations in conjunction with remote sensing data and past observations, to improve our mechanistic understanding of how physical processes drive biology in the Southern Ocean. In Chapter 2, I show how different mechanistic pathways can control population dynamics from the bottom-up (via light, nutrients), as well as the top-down (via grazing pressure). In Chapters 3 and 4, I employ a higher resolution, eddy resolving, integration to explicitly track and examine closed eddy structures and address how they modify biomass at the mesoscale.<br>Chapter 3 considers how simulated eddies drive bottom-up controls on phytoplankton growth and finds that division rates are, on average, amplified in anticyclones and suppressed in cyclones. Anomalous division rates are predominately fueled by an anomalous vertical iron flux driven by eddy-induced Ekman Pumping. Chapter 4 goes on to describe how anomalous division rates combine with anomalous loss rates to drive anomalous net population growth. Biological rate-based mechanisms are then compared to the potential for anomalies to evolve strictly via physical transport (i.e. dilution, stirring, advection). All together, I identify and describe dramatic regional and seasonal variability in when, where, and how different mechanisms drive phytoplankton growth throughout the Southern Ocean. Better understanding this variability has broad implications to our understanding of how oceanic biogeochemisty will respond to, and likely feedback into, a changing climate.<br>Specifically, the uncertainty associated with this variability should temper recent proposals to artificially stimulate net primary production and the biological pump via iron fertilization. In Chapter 5 I argue that Southern Ocean Iron Fertilization fails to meet the basic tenets required for adoption into any regulatory market based framework.<br>by Tyler W. Rohr.<br>Ph. D.<br>Ph.D. Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution)
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Meilander, Tracey Trzebuckowski. "The Role of Bacterioplankton in Lake Erie Ecosystem Processes: Phosphorus Dynamics and Bacterial Bioenergetics." [Kent, Ohio] : Kent State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=kent1163880480.
Texte intégralRésumé :
Thesis (Ph.D.)--Kent State University, 2006.<br>Title from PDF t.p. (viewed Mar. 5, 2009). Advisor: Robert T Heath. Keywords: bacterioplankton, phosphorus dynamics, bacterial bioenergetics, labile dissolved organic carbon, bacterial productivity, bacterial respiration, bacterial growth efficiency, Lake Erie, hypoxia. Includes bibliographical references (p. 357-397).
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Gimenes, Manuela Vieira. "Virioplâncton na Amazônia: estudo da diversidade dos vírus das famílias Phycodnaviridae e Myoviridae nos rios Negro, Solimões e Cuieiras." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/42/42132/tde-10012011-084849/.
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O virioplâncton é o mais diverso e o mais abundante componente do plâncton, o qual exerce grande importância ecológica, estando envolvido em processos de ciclagem de nutrientes, diversificação e distribuição de algas e bactérias, controle de florações fitoplanctônicas, formação de nuvens e transferência gênica horizontal. Os objetivos deste projeto foram analisar as populações das famílias Phycodnaviridae e Myoviridae, nos rios Cuieiras, Negro e Solimões (AM), e determinar um possível impacto do lançamento de efluente doméstico sobre essas populações. Miofagos foram detectados nas amostras dos 3 rios estudados, enquanto que os ficodnavírus somente foram encontrados nos rios Solimões e Cuieiras. Análises filogenéticas revelaram que os miofagos não se agrupam em função das características do ambiente nem da localidade, diferentemente dos ficodnavírus. A interferência do lançamento de efluentes domésticos sobre as características da água e sobre as populações locais das famílias Phycodnaviridae e Myoviridae e fitoplanctônicas não foi observada.<br>The virioplankton is the most diverse and abundant plankton component, which exerts great ecological importance by being involved in processes such as nutrient cycling, diversification and distribution of algae and bacteria, bloom termination, cloud formation and horizontal gene transfer. The aims of the present work were to analyze the viral populations of Phycodnaviridae and Myoviridae families from the Cuieiras, Negro and Solimões rivers (AM), and to determine whether or not sewage discharge in the area is affecting these populations. Myophages were detected in all samples from the 3 studied rivers while phycodnaviruses were only found in the Solimões and Cuieiras rivers. Phylogenetic analyses revealed that myophages do not cluster accordingly neither to the environment nor to the location, differently from phycodnaviruses. The interference of sewage discharge on the water characteristics and the local viral (phycodnavirus and myophage) and phytoplanktonic populations was not detected.
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Harlin, Hugo. "2D Modelling of Phytoplankton Dynamics in Freshwater Lakes." Thesis, Uppsala universitet, Avdelningen för beräkningsvetenskap, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-388868.
Texte intégralRésumé :
Phytoplankton are single celled organisms capable of phytosynthesis, and are present in all the major oceans and lakes in the world. Phytoplankton contribute to 50% of the total primary production on Earth, and are the dominating primary producer in most aquatic ecosystems. This thesis is based on the 1D deterministic model by Jäger et. al. (2010) which models phytoplankton dynamics in freshwater lakes, where phytoplankton growth is limited by the availability of light and phosphorus. The original model is here extended to two dimensions to include a horizontal dimension as well as a vertical dimension, in order to simulate phytoplankton dynamics under varying lake bottom topographies. The model was solved numerically using a grid transform and a finite volume method in MATLAB. Using the same parameter settings as the 1D case studied by Jäger et. al. (2010), an initial study of plankton dynamics was done by varying the horizontal and vertical diffusion coefficients independently.
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Hellekant, Nils. "Adaptive Evolution of Resource Use, Phenotypic Diversity, and Productivity of Phytoplankton Communities." Thesis, Umeå universitet, Institutionen för fysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-161240.
Texte intégralRésumé :
There is growing concern that the worldwide loss in biodiversity will harm the stability of the ecosystems, and thereby, the carrying capacity and critical ecosystem services the biosphere provides. Phytoplankton (microalgae) in lakes and oceans are arguably the most important primary producers. They are responsible for approximately half of the earth's primary production. However, there is little research into what influences the biodiversity of phytoplankton communities and of those studies the mechanisms for coexistence of phytoplankton have so far almost exclusively been studied on ecological time scales. We, therefore, explored how biodiversity and biomass (a proxy to primary production) of phytoplankton communities respond to co-varied environmental drivers over evolutionary time scales. We model adaptive evolution of phytoplankton' resource use, with a non-dimensionalized model of negatively buoyant phytoplankton inhabiting a partially mixed one-dimensional water column using reaction-advection-diffusion equations. We show that a number of environmental drivers have novel effects on biodiversity and biomass on evolutionary timescales. In contrast with previous non-evolutionary work, we found that decreasing light attenuation or increasing resource use efficiency can result in decreased biomass of plankton communities and nutrient-poor environments. One novel driver of species diversity was the combination of low rates of diffusion with relatively intermediate rates of sinking promote species diversity. Furthermore, we show that the phytoplankton turnover rate affects environmental heterogeneity and is, therefore, a contributing driver to species diversity.The evolution of half saturation constants can produce a variety of biodiversity-ecosystem function patterns as two positive, one unimodal, and one negative association were found when comparing biodiversity-ecosystem function. Collectively, our analyses suggest that environmental drivers can have substantially different effects over evolutionary timescales than those effects ecological modeling has previously shown.
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Ballón, Soto Roberto Michael. "Étude acoustique du macrozooplancton au Pérou : estimation de biomasse, distribution spatiale, impact du forçage physique, et conséquences sur la distribution des poissons fourrage." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20052/document.
Texte intégralRésumé :
La partie nord du Système du courant de Humboldt (NSCH) couvre moins de 0.1% de la surface océanique mondiale mais produit plus de poisons, en particulier d'anchois du Pérou (Engraulis ringens), par unité de surface que n'importe quelle autre région du monde. Bien que ce système produise suffisamment de macrozooplancton pour alimenter les populations de poisson fourrage, le manque d'informations sur ce compartiment limite nos capacités d'étude. L'objectif de cette thèse est d'étudier la dynamique de la distribution spatiotemporelle de la biomasse en macrozooplancton du NSCH en relation avec l'environnement physique et les poissons fourrage, à différentes échelles. Pour ce faire une méthode acoustique bi-fréquences a été développée et appliqué à des séries de données acoustiques historiques. Des informations à haute résolution ont ainsi pu être extraite sur la biomasse et les patrons de distribution du macrozooplancton, de la galathée pélagique 'munida', des poissons et des autres compartiments. Cette méthode nous a également permis d'estimer l'extension verticale de la communauté épipélagique (ZVEEC). Nous avons démontré que ZVEEC coïncide avec la limite supérieure de la zone de minimum d'oxygène (ZMO), ce qui permet de produire des donnés spatialisées à haute résolution de la limite supérieure de la ZMO et d'estimer le volume d'habitat de l'anchois. Notre estimation de biomasse en macrozooplancton, environ quatre fois supérieures aux estimations antérieures, est en accord avec les découvertes récentes sur l'écologie trophique des poissons fourrage du NSCH et fournit des éléments étayant les théories actuelles sur l'origine de la haute productivité en poissons du NSCH. L'étude des impacts des structures physiques de submeso- et mesoéchelle sur la distribution du macrozooplancton supporte l'hypothèse d'une structuration de type 'bottom-up'. Nous avons également mis en évidence l'impact de la structuration spatiale du macrozooplancton sur la distribution des poissons fourrage. Les données physiques et biologiques à haute résolution obtenues grâce à cette étude ouvrent de nouvelles perspectives pour réaliser des études écologiques intégrées à échelles multiples et pour calibrer les modèles biogéochimiques, trophiques ou End-to-End<br>The Northern Humboldt Current system (NHCS) represents less than 0.1% of the world ocean surface but produces more fish, mainly Peruvian anchovy (Engraulis ringens), per unit area than any other region in the world. Although this system produces enough macrozooplankton to feed its high production of forage fish, the paucity of information on zooplankton hampers research in the system. The objective of this study was to investigate the multiscale dynamics of the spatiotemporal distribution of the macrozooplankton biomass off Peru in relation to the physical environment and their fish predators. For that a bi-frequency acoustic method was developed and applied to extract, from historical acoustic data, high-resolution information on the biomass and the patterns of distribution of macrozooplankton, the pelagic red squad 'munida', fish and other marine compartments. This method also allows estimating the vertical extension of this epipelagic community (ZVEEC). We demonstrated that ZVEEC coincide with the upper limit of the oxygen minimum zone (OMZ), which allowed both producing high-resolution spatial data of the upper limit of the OMZ and estimating the volume habitat of anchovy. The estimated macrozooplankton biomass was about four times higher than previously reported. This estimate is in agreement with the recent findings on forage fish trophic ecology and supports the current hypotheses explaining the NHCS high fish production. The study of the impacts of the submeso- and mesoscale physical structures on macrozooplankton provided evidence of the bottom-up physical effect on the distribution of macrozooplankton biomass. We also found further evidence of the structuring bottom-up effect that macrozooplankton exert on forage fish. The high-resolution biological and physical data obtained in this study opens new perspective to perform integrated multiscale ecological studies and to calibrate biogeochemical, trophic and End-to-End models
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Beaugrand, Grégory. "Biodiversité pélagique et changements hydroclimatiques dans l'océan Atlantique Nord." Paris 6, 2001. http://www.theses.fr/2001PA066390.
Texte intégral
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Vincent, Flora. "Diatom interactions in the open ocean : from the global patterns to the single cell." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCB094/document.
Texte intégralRésumé :
Les diatomées sont des micro-algues unicellulaires, qui jouent un rôle primordial dans l’eco-système marin. En effet, elles sont responsables de 20% de l’activité photosynthétique sur Terre, et sont à la base de la chaîne alimentaire marine, toujours plus menacée par le changement climatique. Les diatomées établissent diverses interactions microbiennes avec des organismes issus de l’ensemble de l’arbre du vivant, à travers des méchanismes complexes tels que la symbiose, le parasitisme ou la compétition. L’objectif de ma thèse a été de comprendre comment ces interactions structurent la communauté du plancton, à grande échelle spatiale. Pour ce faire, j’ai développé de nouvelles approches basées sur le jeu de données inédit de Tara Océans, une expédition mondiale qui a exploré la diversité et les fonctions des microbes marins, en récoltant plus de 40.000 échantillons à travers 210 sites autour du monde. Grâce à l’analyse de réseaux de co-occurrence microbiens, je montre d’une part que les diatomées agissent comme des « ségrégateurs répulsifs » à l’échelle globale, en particulier envers les organismes potentiellement dangeureux tels que les prédateurs et les parasites, et d’autre part que la co-occurrence des espèces ne s’explique qu’en minorité par les facteurs environnementaux. Grâce à la richesse des données Tara Océans, j’ai par ailleurs permis la charactérisation d’une interaction biotique impliquant une diatomée et un cilié hétérotrophe à l’échelle de l’eco-système, illustrant de surcroît le succès des approches dirigées par les données. Dans l’ensemble, ma thèse contribue à notre compréhension des interactions biotiques impliquant les diatomées, de l’échelle globale à la cellule unique<br>Diatoms are unicellular photosynthetic microeukaryotes that play a critical role in the functioning of marine ecosystems. They are responsible for 20% of global photosynthesis on Earth and lie at the base of marine food webs, ever more threatened by climate change.Diatoms establish microbial interactions with numerous organisms across the whole tree of life, through complex mechanisms including symbiosis, parasitism and competition. The goal of my thesis was to understand how those biotic interactions structure the planktonic community at large spatial scales, by using new approaches based on the unprecedented Tara Oceans dataset, a unique and worldwide circumnavigation that collected over 40.000 samples across 210 sites to explore the diversity and functions of marine microbes. Through the analysis of microbial association networks, I show that diatoms act as repulsive segregators in the ocean, in particular towards potentially harmful organisms such as predators as well as parasites, and that species co-occurrence is driven by environmental factors in a minority of cases. By leveraging the singularity of the Tara Oceans data, I provide a comprehensive characterization of a prevalent biotic interaction between a diatom and heterotrophic ciliates at large spatial scale, illustrating the success of data-driven research. Overall, my thesis contributes to our understanding of diatom biotic interactions, from the global patterns to the single cell
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Rosero, Edith Mariela Burbano. "Frequência e diversidade de colifagos somáticos isolados de amostras de água do mar, plâncton e bivalves da baixada santista, canal de São Sebastião e Ubatuba." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/42/42132/tde-23102009-153715/.
Texte intégralRésumé :
Os colifagos somáticos (CS) são os melhores indicadores de poluição fecal. Neste trabalho, foi determinada a abundância de CS em amostras de água do mar, plâncton, e bivalves coletadas em Santos, São Sebastião e Ubatuba. Houve correlação positiva entre CS e as bactérias marinhas viáveis, coliformes termotolerantes, E.coli e enterococos intestinais, e a correlação foi negativa com a temperatura. As maiores contagens de CS foram obtidas em Santos. As freqüências das famílias encontradas nas amostras de água do mar e plâncton foram: Siphoviridae (50% e 65,8%), Podoviridae (36% e 15,8%), Microviridae (9% e 15,8%) e Myoviridae (5%, 2,6%), respectivamente. Em bivalves, só foi observada Siphoviridae. Os morfotipos observados foram A1 (3%), B1 (63%), C1 (21%) e D1 (13%). As técnicas de RFLP e rep-PCR não foram discriminatórias. 9,6% dos colifagos apresentaram os genes que codificam para as toxinas ST e/ou LT. O presente estudo está identificando os colifagos como perigos microbiológicos e gerando subsídios para avaliação de riscos microbiológicos no ecossistema marinho.<br>The somatic coliphages (SC) are the better indicator for fecal pollution. In this research, it was obtained the SC abundance in seawater, plankton and bivalves samples collected from Santos, São Sebastiâo and Ubatuba. SC counts were correlated with marine viable bacteria, thermotolerant coliforms, E. coli and intestinal enterococci, and the correlation was negative with the temperature. Highest SC counts were obtained from samples collected at Santos. The frequency of SC families found in seawater and plankton samples were: Siphoviridae (50% and 65.8%), Podoviridae (36% and 15.8%), Microviridae (9% and 15.8%), and Myoviridae (5%, 2.6%), respectively. In bivalves, only Siphoviridae was found. Morphotypes A1 (3%), B1 (63%), C1 (21%) and D1 (13%) were observed. The RFLP and rep-PCR techniques were not discriminatory. 9.6% of coliphages contained genes codifying for thermostable toxin (ST) and/or thermolabil toxin (LT). This study is identifying the coliphages as microbial hazard and giving support to later studies for microbial risk assessment of marine ecosystem.
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Andrianjakarivony, Felana Harilanto. "Caractérisation du virome d’un écosystème tropical fortement anthropisé : la lagune Ebrié en Côte d’Ivoire." Electronic Thesis or Diss., Aix-Marseille, 2022. http://www.theses.fr/2022AIXM0579.
Texte intégralRésumé :
Dans cette thèse, nous avons choisi d’étudier la composante virale d’un site lagunaire exposé aux rejets domestiques, agricoles et industriels : la Lagune Ebrié bordée par la ville d’Abidjan, en Côte d’Ivoire. Les objectifs de cette thèse visaient (1) à caractériser les viromes benthiqes et planctoniques dans 7 sites de cette lagune présentant des niveaux d'eutrophisation contrastés, en distinguant les viromes ADN et ARN, et (2) à examiner les stratégies de reproduction virale. Pour cela, une approche métagénomique shotgun combinée à des analyses bioinformatiques a été utilisée. Nous avons montré que la composition des viromes ADN était spécifique à chaque compartiment (plancton/benthos). À l’inverse, la composition des viromes ARN était plus influencée par le niveau d’eutrophisation du milieu. Les viromes des sites les plus eutrophisés présentaient des séquences associées aux pathogènes humains d'origine fécale et aux indicateurs de pollution fécale humaine. L’étude des interactions entre les virus et leurs hôtes bactériens, a permis de montrer que cette lagune tropicale était plus propice aux stratégies lytiques de reproduction virale dans les stations les plus eutrophes. Enfin, en utilisant une approche basée sur la prédiction théorique des hôtes bactériens, nous avons pu montrer la fiabilité de l’approche choisie générant des profils taxonomiques bactériens comparables à ceux obtenus par l’approche classique basée sur le métabarcoding ciblant le gène ARN 16S. Ce travail de thèse a donc permis d’apporter un jeu de données unique, mais aussi de nouvelles connaissances fondamentales sur la composition du virome de sites aquatiques soumis à de forts niveaux de pollution.u<br>In this thesis, we chose to study the viral community in a tropical lagoon exposed to domestic, agricultural and industrial discharge : the Ébrié Lagoon bordering the city of Abidjan in the Ivory Coast. The objectives of this study were (1) to characterize the benthic and planktonic viromes in seven sites in the lagoon with contrasting levels of eutrophication, distinguishing between DNA and RNA viromes, and (2) to examine the reproductive strategies of viruses. To this end, we used shotgun metagenomic sequencing combined with bioinformatics analysis. The key findings showed that the composition of DNA viromes was specific to each compartment (plankton/benthos). Conversely, the composition of RNA viromes was more influenced by the level of eutrophication than by the compartment. Viromes of the most eutrophicated sites contained sequences associated with human pathogens of faecal origin and with indicators of human faecal pollution. The study of interactions between the viruses and their bacterial hosts showed that the most eutrophic sites in this tropical lagoon were more conducive to lytic viral reproductive strategies, while lysogeny was more common in the most oligotrophic sites. Lastly, the results of an approach based on the theoretical prediction of bacterial hosts via the Prokaryotic virus Host Predictor indicated the reliability of this tool in generating taxonomic profiles of bacterial hosts comparable to those obtained by the classical approach based on metabarcoding targeting the 16S rRNA gene. This study provided not only a unique dataset, but new fundamental knowledge on the composition of the virome of aquatic sites subjected to high levels of pollution
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Reboul, Guillaume. "Metabarcoding and metagenomic approaches to decipher microbial communities in suboxic environments Microbial eukaryotes in the suboxic chemosyn- thetic ecosystem of Movile Cave, Romania Hyper- diverse archaea near life limits at the polyextreme geothermal Dallol area Performance of the melting seawater-ice elution method on the metabarcoding characterization of benthic protist communities Core microbial communities of lacustrine microbialites sampled along an alkalinity gradient Environmental drivers of plankton protist communities along latitudinal and vertical gradients in the oldest and deepest freshwater lake Ancient Adaptive Lateral Gene Transfers in the Symbiotic Opalina-Blastocystis Stramenopile Lineage Marine signature taxa and microbial community stability along latitudinal and vertical gradients in sediments of the deepest freshwater lake." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASL041.
Texte intégralRésumé :
L’écologie microbienne concerne l’étude des microorganismes et de leurs interactions biotiques et abiotiques dans un écosystème donné. Ces vingt dernières années, l’avancement des techniques moléculaires pour analyser la diversité microbienne et, notamment, les nouvelles technologies de séquençages (NGS) ont permis de surmonter les limitations associées aux approches traditionnelles basées sur la culture et la microscopie. Ces approches moléculaires ont conduit à une accumulation des données de diversité microbienne et de potentiel métabolique dans des communautés microbiennes des écosystèmes variés.Cependant, ces efforts ont été principalement appliqués sur des environnements facilement accessibles ou liés à l’humain, comme le plancton (marin principalement) et la flore intestinale. Néanmoins, ceci a conduit à une très forte augmentation de données environnementales et au développement de la bioinformatique par le biais de nombreux outils. Parmi les environnements délaissés des études, les environnements faibles en oxygène sont probablement également porteurs de nouveautés phylogénique ou métaboliques.Afin de palier à cela, nous avons choisi d’explorer deux environnements suboxiques relativement peu étudiés : la cave Movile (Roumanie) et les sédiments du lac Baikal (Sibérie, Russie). Notre but étant de montrer les diversités phylogénétiques et fonctionnelles des microbes de ces biotopes.Pour cela, j’ai d'abord développé un pipeline d’analyse de données métabarcoding (petite sous-unités ribosomique). Ensuite, j’ai appliqué cet outil sur des données de métabarcoding de protistes provenant d’échantillons d’eau et de tapis microbiens de la cave de Movile, un écosystème chemosynthétique pratiquement fermé. Nous avons montré que la diversité des protistes de la cave s’étendait à quasiment tous les grands groupes eucaryotes et provenait à la fois d’origine d’eaux douces et marines. De plus, la plupart ont été affiliées à des groupes d’organismes typiquement anaérobies, ce qui est concordant avec les paramètres abiotiques de la cave. Écologiquement, ces protistes sont des prédateurs mais aussi vraisemblablement des partenaires symbiotiques avec des espèces procaryotes de la cave.Dans une deuxième étude, j’ai eu l’opportunité d’appliquer ce pipeline de métabarcoding sur des données procaryotes et eucaryotes provenant des couches superficielles des sédiments du lac d’eau douce Baikal. Comme attendu, les communautés microbiennes dans ces sédiments sont particulièrement diverses et relativement enrichis en archées. Nous avons aussi pu mettre en évidence des lignées que l’on pensait exclusivement marines dans ces sédiments. Ces lignées sont probablement planctoniques mais s’accumulent au fond par sédimentation. Enfin, les échantillons ont été prélevés dans le but de tester les influences de la profondeur, du bassin et de la latitude sur les communautés. Aucune d’elles ne s’est révélée significative.Dans une troisième étude, j'ai utilisé une approche métagénomique afin de révéler les acteurs écologiquement majeurs dans les sédiments, leurs rôles et de reconstruire leurs génomes. Cela nous a permis notamment de mettre en évidence le rôle primordial des Thaumarchaeota dans le cycle de l’azote et la production primaire de molécules de carbone. Les chloroflexi et les protéobacteries ont aussi un rôle important dans la surface des sédiments du lac Baikal. Ce travail de thèse participe à la connaissance globale de la diversité microbienne sur la planète en mettant en lumière des environnements peu étudiés. De plus, l’étude de la surface des sédiments du lac Baikal apporte de nouvelles données sur le sujet de la transition eau douces/eau marines des microbes. Enfin, la métagénomique a permis de révéler le cycle des nutriments et les microorganismes y participant dans ces échantillons de sédiment. En résumé, ce travail vient mettre en lumière l’écologie microbienne d’écosystèmes suboxiques, notamment la surface des sédiments du lac Baikal<br>Microbial ecology is the science of micro-organisms and their biotic and abiotic interactions in a given ecosystem. As technology has advanced, molecular techniques have been widely used to overcome the limitations of classical approaches such as culturing and microscopy. Indeed, the development of Next Generation Sequencing (NGS) technologies in the past twenty years has largely helped to unravel the phylogenetic diversity and functional potential of microbial communities across ecosystems.Nonetheless, most of the environments studied through these techniques concentrated on relatively easily accessible, tractable and host-related ecosystems such as plankton (especially in marine ecosystems), soils and gut microbiomes. This has contributed to the rapid accumulation of a wealth of environmental diversity and metagenomic data along with advances in bioinformatics leading to the development of myriads of tools. Oxygen-depleted environments and especially their microbial eukaryote components are less studied and may lead to future phylogenetic and metabolic discoveries.In order to address this, we conducted analyses on two poorly studied suboxic ecosystems: Movile Cave (Romania) and lake Baikal sediments (Siberia, Russia). In this task, we aimed at unveiling the taxonomic and functional diversity of microorganims in these environments.To do so, I first evaluated the available bioinformatics tools and implemented a bioinformatics pipeline for 16S/18S rRNA gene-based metabarcoding analysis, making reasoned methodological choices. Then, as a case study, I carried out metabarcoding analyses of the water and floating microbial mats found in Movile Cave in order to investigate its protist diversity. Our study showed that Movile Cave, a sealed off chemosynthetic ecosystem, harbored a substantial protist diversity with species spanning most of the major eukaryotic super groups. The majority if these protists were related to species of freshwater and marine origins. Most of them were putatively anaerobic, in line with the cave environment, and suggesting that in addition to their predatory role, they might participate in prokaryote-protist symbioses.In a second study, I applied my metabarcoding pipeline to explore unique and relatively unexplored environment of Lake Baikal sediments. I first applied a metabarcoding approach using 16S and 18S rRNA genes to describe prokaryotic as well as protist diversity. Overall, the communities within these ecosystems were very diverse and enriched in ammonia-oxidizing Thaumarchaeota. We also identified several typical marine taxa which are likely planktonic but accumulate in sediments. Finally, our sampling plan allowed us to test whether differences across depth, basin or latitude affected microbial community structure. Our results showed that the composition of sediment microbial communities remained relatively stable across the samples regardless of depth or latitude.In a third study, we applied metagenomics to study the metabolic potential of communities associated to Baikal sediments and to reconstruct metagenome-assembled genomes (MAGs) of dominant organisms. This revealed the considerable ecological importance of Thaumarchaeota lineages in lake Baikal sediments, which were found to be the major autotrophic phyla and also very implicated in the nitrogen cycle. Chloroflexi and Proteobacteria-related species also appeared ecologically important.This PhD thesis reveals the taxonomic diversity of poorly studied suboxic ecosystems and therefore contributes to our knowledge of microbial diversity on Earth. Additionally, the analyses of surface sediment samples in lake Baikal adds new light on freshwater-marine transitions. The metagenomic analyses reported here allowed us to postulate a model of nutrient cycle carried out by microorganismsin these sediments. Overall, this work sheds light on the microbial ecology of oxygen-depleted environments, and most notably lake Baikal surface sediments
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Healey, Katherine Margaret. "Perturbation dynamics of a planktonic ecosystem." Thesis, 2008. http://hdl.handle.net/1828/1028.
Texte intégralRésumé :
Planktonic ecosystems provide a key mechanism for the transfer of CO2 from the atmosphere to the deep ocean via the so-called "biological pump". Mathematical models of these ecosystems have been used to predict CO2 uptake in surface waters, and more recently have been embedded in global climate models.
While the equilibrium properties of these models are well studied, less attention has been paid to their response to external perturbations, despite the fact that as a result of the variability of environmental forcing such ecosystems are rarely, if ever, in equilibrium. Human induced perturbations to these ecosystems, namely the addition of limiting nutrients (e.g. iron) to areas where nitrate is plentiful to accelerate the biological pump, have been proposed as a solution to reduce atmospheric CO2. Linear theory is used to determine the structure of "unit-norm" perturbations (size in mmol N m^-3) to state variables of an ecosystem model in steady state, describing Ocean Station P (50N 145W) in summer, that optimize either instantaneous export flux of organic matter at fixed times or integrated export as the ecosystem relaxes towards equilibrium. For all perturbations, the flux to higher trophic levels is the primary contributor to export flux, the contribution of aggregation is negligible, and (sinking) detritus increases significantly in the transient dynamics. Two perturbations considered optimize instantaneous export flux; both perturbations synchronize P1 and Z1 relative to their predator prey cycle, resulting in a maximum instantaneous export flux of 4.4 mmol N m^-2 d^-1, and also increased integrated export above that at steady state (6 g C m^-2 over 150 days). An increase in larger phytoplankton (P2), representing diatoms, results in the highest integrated export (7 g C m^-2). The perturbations in which P2 persist the longest give the highest integrated export, and these perturbations are primarily increases in P2.
The additional integrated export in response to a proportional increase to steady state concentrations of both large and small phytoplankton is positive, but much lower than the optimal perturbations. However, the additional integrated export in response to an increase in only P1 is negligible.
The linear and nonlinear ecosystem and export responses to two perturbations are compared; for perturbations of magnitude 0.5 mmol N m^-3, the linearization of the ecosystem dynamics, rather than of the export flux, is the primary cause for differences between the fully linear and fully nonlinear cases.
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Miao, You-Chun, and 苗祐軍. "Planktonic community respiration and organic carbon cycle in a coral reef ecosystem: Nan-Wan Bay, southern Taiwan." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/67733441054640457511.
Texte intégralRésumé :
碩士<br>國立臺灣師範大學<br>生命科學研究所<br>95<br>The purpose of this study is to understand potential factors impact on planktonic community respiration (CR) and organic carbon cycle in the water column of coral reef ecosystem in the Nan-Wan Bay, southern Taiwan. Results showed that CR varied between 1.7~ 213 mg C m-3 d-1 during study period. Further analysis showed that the rate was mainly determined by biomass and production of planktonic community, especially phytoplankton. This assumption can be evident by significant relationships observed between integrated values over euphotic zone of CR versus chlorophyll a (Chl-a; 1.8~67 mg Chl m-2) and primary production (PP; 43~569 mg C m-2 d-1; all p < 0.05). In addition, Results also showed that integrated bacterial biomass (BB; 11~1313 mg C m-2) and production (BP; 18~823 mg C m-2 d-1) were significantly regressed against both dissolved and particulate organic carbon (all p<0.01). It suggests that growth of heterotrophic bacteria in this coral reef system might be limited by the amount of organic substrates. The mean ratio of primary production to community respiration (i.e., P/R ratio) was 0.38 ± 0.51, and this indicates that the ecosystem of water column in the Nan-Wan Bay is heterotrophic. This result also suggests that allochthonous organic carbon is needed to support the organic carbon consumption, and organic exudates from the benthos, e.g., corals, might be the most important source in this coral reef ecosystem.
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Laurenceau, EC. "Ecosystem controls on carbon export efficiency from the naturally iron-fertilised phytoplankton bloom over the Kerguelen Plateau." Thesis, 2015. https://eprints.utas.edu.au/23226/1/Laurenceau_whole_thesis.pdf.
Texte intégralRésumé :
In the ocean, the perpetual 'snowfall' of biogenic marine particles exports organic carbon from the well-lit surface layer to the deep sediments, promoting its sequestration. The efficiency of this 'biological carbon pump' (BCP), presents strong spatio-temporal variations that are not yet fully explained. Changes in surface plankton communities and trophic interactions appear important because they lead to modifications of sinking particle characteristics (e.g. composition, structure, sinking velocity). These controls are explored here via the characterization of sinking particles originating from varying planktonic community structures and evaluation of their ability to export carbon. During the second KErguelen Ocean and Plateau compared Study (KEOPS2) conducted in Oct.-Nov. 2011, six sites were sampled over and downstream of the Kerguelen Plateau (Southern Ocean), where a mosaic of phytoplankton blooms of changing communities forms in response to natural iron fertilisation. Sinking particles were collected with free-drifting sediment traps at four mesopelagic depths to examine their form and composition, including optical characterization using polyacrylamide gel filled traps. Concurrently, aggregates were formed in roller tanks from surface water phytoplankton assemblages, to explore the intricate influences of particle size, structure and composition on the sinking velocity. At each site, carbon export efficiencies were calculated as the ratio of carbon flux to net primary productivity (e-ratio).
High productivity was associated with the lowest carbon export efficiency (e-ratio ~0.02) while maximum export efficiency (e-ratio ~0.2) was found at low-productivity sites. Two explanations were identified. Firstly, at high-biomass sites, strong zooplankton grazing generated large fecal pellets sustaining high carbon fluxes at 100-200 m (180 mg C m⁻² d⁻¹). This export pathway represented a 'dead end' due to rapid attenuation of the fecal pellet flux at 200-400 m, releasing most of the carbon (48±21 % carbon flux decrease). Secondly, based on the roller tank results, the morphology of dominant diatom species appeared to be an important control on aggregate sinking velocities, possibly via species-specific coagulation efficiency affecting particle structure and density. At high-biomass sites, dominant small spine-forming species formed loose slow-sinking aggregates (~10 m d⁻¹), whereas chain-forming diatoms without spines, at low-productivity sites, produced compact fast-sinking aggregates (~250 m d⁻¹). The similarity of aggregate morphology and structure from roller tank and gel traps (2-D fractal number = 1.8 and 1.9 respectively), increased confidence in applying these results to in situ conditions. A generic 3-D physical-biogeochemical (BGC) model was modified to investigate conceptually the influence of planktonic community variations on carbon export efficiency through their control on detritus composition and sinking velocity. This was achieved by introducing in the model a variable detritus sinking velocity based on phytoplankton and zooplankton detrital fractions (using experimental results). Changes from a constant (100 m d⁻¹) to a variable sinking velocity induced a significant increase of the annual integrated carbon flux at 100 m (45±23 %) highlighting the importance of sinking velocity parameterisation in BGC models. Simulations indicate that export efficiency could depend upon subtle trophic interactions between phyto- and zooplankton communities influencing the relative rates of productivity and associated carbon flux and determining the conditions of biomass retention or export. The insights and tools developed here improve our understanding of how a climate-mediated shift of surface plankton communities can alter the efficiency of the BCP.
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Lai, Chao-Chen, and 賴昭成. "Temperature effects on plankton community respiration in a subtropical freshwater ecosystem." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/sf6cc5.
Texte intégralRésumé :
博士<br>國立臺灣大學<br>海洋研究所<br>105<br>With a ten-year weekly to biweekly data set taken from a P-limited subtropical reservoir, this study intends to explore the potential mechanisms in controlling the temporal variation of plankton community respiration rate (CR) and bacterial respiration rate (BR). Summer not only had high CR and BR value, but also high variation. The results showed that CR, BR, specific plankton community respiration (SCR), and specific bacterial respiration (SBR) all correlated with temperature significantly (p < 0.05). Activation energy, Ea, of CR is 0.80±0.04, SCR is 0.34±0.06, BR is 0.93±0.06, and SBR is 0.39±0.06. The results also indicated that temperature might be the major controlling factor for CR and BR. We also found that Ea-BR is high than Ea-CR, which indicate that BR was more sensitive to temperature than CR.
Temperature manipulation experiment provide a situation to estimate temperature effect in wilder range. However, the most common characteristic of temperature response, activation energy (Ea), might be more variation. Our result combined two years temperature manipulation, the result proved that BR is more sensitive than CR either short-term temperature change (CR:0.69 and BR: 1.07) or long-term seasonal variation(CR: 0.67 ± 0.05 and BR:0.94 ± 0.08). Temperature change would increase system unstability. Two years result comparison showed that environmental condition would affect result warming.
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Hall, Spencer Ryan. "Species sorting and biomass partitioning along light : nutrient predation risk gradients in planktonic pond ecosystems /." 2003. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3097111.
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Shajina, I. "Statistical evaluation of plankton diversity in mangrove ecosystems in Cochin area." Thesis, 1992. http://eprints.cmfri.org.in/11133/1/Shajina%20I..pdf.
Texte intégralRésumé :
Mangroves are unique ecosystems which provide food, fodder and
a host of other products to the coastal populations in tropical and subtropical areas. They help in preventing natural calamities such as large scale soil erosion and floods. Mangroves characterise an ecosystem where both terrestrial and aquatic fauna interact and strike a perfect balance. Due to the presence of high organic matter these areas act as important
nursery grounds for a number of finfishes and shellfishes. The export of nutrients and rich detrital load from mangroves to adjoining areas such as estuaries makes these locations also important in the context of fishery. Mangroves are also important from the view of aquaculture. These areas with suitable modifications can be converted into culture
ponds with high rate of production.
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Evans, R. "An integrated study of a rapidly changing continental shelf ecosystem : linking physical conditions, prey field dynamics and top predator behaviour through a marine heatwave event." Thesis, 2019. https://eprints.utas.edu.au/33605/1/Evans_whole_thesis.pdf.
Texte intégralRésumé :
The land-sea interface provides some of the world’s most valuable and biodiverse habitats, despite being exposed to anthropogenic pressures. Marine predators which cross this interface are particularly vulnerable, with human activities in coastal zones diminishing both the quality and availability of suitable breeding and foraging areas. These predators are constrained to forage in smaller oceanic regions while rearing young on-land, therefore their reproductive success is intrinsically linked to the productivity of nearshore waters. Changing environmental conditions, as a direct and indirect consequence of climate change, can alter the structure, distribution and community composition of lower-trophic level prey. In order to predict the response of ecosystems to this change, and to changes as a result of extreme events such as marine heatwaves (MHW), an in depth understanding of the links between environmental factors, prey-field dynamics and predator behaviour is needed.
The continental shelf to the south-east of Tasmania is a hotspot of biodiversity, where seasonal productivity supports a large and diverse array of marine birds and mammals. However, this region is also subject to rapid environmental change, being situated within the south-east Australian climatic-hotspot. Due to the intensification and increasing southward penetration of the East Australian Current (EAC), a major western boundary current running from the sub-tropical Coral Sea to the south-east coast of Australia, warming is occurring at an accelerated rate. Quantifying how prey-field dynamics respond to these changing environmental conditions, and the flow-on effects to the behaviour of apex predators, formed the main objective of this study. Surveys were conducted over a three-year period (2015-2018), during which a prolonged marine heatwave (MHW) event occurred that increased water temperatures of the entire western Tasman Sea by a mean of 2.9°C above climatology for 251 days. To develop an integrated understanding of ecosystem dynamics through a period of high environmental variability, zooplankton prey-field dynamics, fish school presence, little penguin (Eudyptula minor) foraging behaviour, and the distribution and abundance of key bird species were analysed in relation to local environmental factors.
Zooplankton community composition and abundance were examined in relation to environmental drivers. Generalised additive models (GAMs) indicated a significant decrease in community abundance during the MHW, with a shift in species assemblages away from temperate species and towards EAC-associated species. The size structure of the zooplankton community was also analysed using the normalised biomass size spectra (NBSS). The NBSS is an effective way to demonstrate the variability present in a community, in terms of gains and loss of energy through respiration, predation and mortality. It can also be indicative of changes to the equilibrium of a community. Strong seasonality was detected in the results, with temperature, current velocity and mixed-layer depth being significant drivers of variability in the NBSS.
These lower trophic level dynamics were linked to the behaviour of top predators through a detailed case study of the at-sea habitat preference of little penguins breeding in south-east Tasmania (n=13). Tracking was conducted over two summer periods, in 2016 during the MHW, and in 2018 under cooler and more stable environmental conditions. Habitat models (species distribution models) were developed to asses spatial distribution patterns and examine the bio-physical factors influencing foraging trips at fine-scale. Regions of higher sea-surface temperature gradients and cooler than average temperatures were found to increase the probability of penguin presence. The predictability of little penguin habitat-use according to prey-type was also assessed by including covariates for the general distribution of resources in the region; e.g. total zooplankton abundance, and the abundance of Australian krill (Nyctiphanes australis), which forms part of little penguin diet. Little penguin foraging areas were more influenced by the distribution of Australian krill than by general zooplankton abundance.
The response of local predators to changes in bio-physical parameters were measured by modelling the distribution of 10 species of seabirds using boosted regression trees. Key species ranged from small planktivores, such as the common diving petrel (Pelecanoides urinatrix), to albatross (family Diomedeidae). Therefore, to encompass the range of prey that underpins the distribution of these species, biological covariates included zooplankton biomass, and the presence (and absence) of fish schools (determined using hydro-acoustics during surveys). Seabird species were separated into feeding groups using multivariate analysis and modelled separately to reveal potential drivers for each group. Despite different biological predictors influencing the distribution of different groups, sea surface temperature was found to explain the greatest amount of variation across all feeding groups. This influence is thought to be prey-mediated, as both biological covariates tested exhibited negative correlations with increasing SST.
Through considering the complex links which exist between predators, their prey and the physical environment, this study produces new insights into the potential effects of extreme events. Further, it improves our understanding of how general warming trends affect prey structure and the possible flow-on effects for predators. Modelling the distribution of apex predators enables the identification of important foraging regions with favourable bio-physical characteristics. We highlight how detailed assessments of ecosystem and environmental interactions can be pivotal to informing the effective management of these vulnerable and biodiverse ecosystems into the future.
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Laurent, Arnaud. "Examining the influence of meteorological events on plankton dynamics in a coastal ecosystem (Lunenburg Bay, Canada)." 2011. http://hdl.handle.net/10222/13707.
Texte intégralRésumé :
Pelagic ecosystems are inherently complex in coastal inlets where they are controlled by physical processes and influenced by biogeochemical and foodweb interactions. Meteorological events are important drivers of this ecological variability. This thesis investigates their effect on the plankton dynamics of Lunenburg Bay, an inlet on the Atlantic coast of Nova Scotia (Canada). In this region, meteorological events are dominated by upwelling in summer, which are a dominant source of flushing and nutrient variability for the inlets. Despite these events, which induce phytoplankton blooms in other regions, the concentration of phytoplankton as chlorophyll remains relatively low throughout the summer in Lunenburg Bay. To reveal the underlying processes limiting the development of phytoplankton biomass, and therefore to improve our understanding of the factors regulating plankton dynamics in this inlet, the objectives of this thesis are to determine the main drivers of variability in phytoplankton biomass and plankton community structure, and to identify the factors limiting the development of phytoplankton biomass in Lunenburg Bay. For that, I use a dataset collected at a coastal observatory located in Lunenburg Bay that covers the years 2003–2006, complemented by a series of transects carried out in summer 2006. The dataset covers physical, chemical and biological properties of the bay, including plankton taxonomy. Two types of physical-biological coupled models are developed: a low-resolution box model of Lunenburg Bay with steady-state wind forcing, and a high-resolution nested model of Lunenburg Bay using the Regional Ocean Modelling System (ROMS) to hindcast a series of upwelling events in 2006. The results reveal that four factors regulate the phytoplankton response to upwelling events in Lunenburg Bay, namely (1) the duration of an upwelling event, (2) the low nitrate concentration in source waters, (3) the flushing rate of the inlet (hence transport), and (4) the bathymetry along the inshore-offshore axis of the bay. In addition, (5) the occurrence of upwelling and (6) the inshore-offshore gradient of increasing depth influence the structure of respectively phytoplankton and zooplankton communities, indicating a dissimilarity in the processes structuring plankton communities in the lower food web. A conceptual model is then developed to describe the role of transport and nitrate concentration in source waters in controlling plankton dynamics in an inlet.
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Quijón, Pedro Armando. "Predator regulation of sedimentary fauna in a sub-Arctic fjord ecosystem / y Pedro Armando Quijón." 2004.
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Sachse, René. "Influence of climate change on lake ecosystems - disentangling physical, chemical and biological interactions." Doctoral thesis, 2014. https://tud.qucosa.de/id/qucosa%3A28696.
Texte intégralRésumé :
Climate change affects lake ecosystems in many ways by direct and indirect temperature impacts on hydrophysical structure, hydrology, chemical cycles and on biological interactions. The identification of these climate signals can be complicated and superimposed by other environmental changes, such as land use changes. The aim of this thesis was to seperate temperature effects from effects of management and other environmental influences and to understand the underlying complex processes causing significant changes of ecosystem states. This understanding is important for decisions of lake and reservoir managers to counteract unfavorable consequences of climate change.
For the recent study, long-term data of meteorological, hydrophysical and biological variables (phytoplankton, crustacean zooplankton, fish) of the German drinking water reservoir Saidenbach were analysed. Based on this long-term data set, strong indicators for climate induced changes have been identified. In particular, increasing water temperatures since 1975, earlier break up of ice covers and an altered hydrophysical structure could be detected. Thereby, stratification stability increased and turbulent mixing decreased in summer. The water of the reservoir warmed more than
the tributaries resulting in a trend to deeper entrainment of the inflows.
As further indicators of climate change, an increased annual biomass of phytoplankton and species shifts in the phytoplankton community in spring and summer had been observed. During the spring mass development, the diatom Aulacoseira subarctica became dominant in recent years with warm winters and early ice-out. Its unusual spatial pattern with occurrences in aphotic depths could be explained by easier resuspension compared to other diatoms. By being resuspended first and establishing a high inoculum, A. subarctica profits from an earlier ice-out and earlier full circulation. In spite of a reduced nutrient loading to the epilimnion, in summer, the diatom Fragilaria crotonensis was displaced increasingly by cyanobacteria. This species shift could be explained well by the hydrophysical regime shift.
Although, the annual total phytoplankton biomass increased since 1990, the crustacean zooplankton in Saidenbach reservoir did not seem to profit from improved food resources. To the contrary, Daphnia abundances reduced tremendously. We could show that the influcence of fish stocks were underestimated. The stocked silvercarp may have contributed up to 70 % of the total zooplanktivorous fish biomass which had a temperature and density dependent effect. The faster growth of Daphnia at higher temperatures could not compensate for the more actively grazing fish when stock of zooplankitvorous fish was too high. Still, temperature was identified as the most important factor that explained 29 % of the zooplankton phenology, while the second most important predictors were zooplanktivorous fish biomass and nutrient loading, explaining 18 % of the variance.
The importance of submerged macrophytes in shallow lakes is well investigated. To increase also the understanding of their impact and their role during climate change on water quality in deep lakes, a model for stratified lakes that includes submerged macrophytes was developed. The simulations showed that macrophyte effects were mainly positive for water quality and macrophytes in deep lakes were able to potentially reduce summer phytoplankton, especially cyanobacteria by 50 % in 11 m deep and still by 15 % in 100 m deep oligotrophic lakes. Nutrient competition with phytoplankton contributed most to this macrophyte effect. In conclusion, for deep lake restoration the re-establishment of submerged macrophytes might be as important as for shallow lakes. The full lake model includes hydrophysical and ecological submodules and thus will allow further comprehensive climate simulations and the evaluation of the effectivity of adaptive strategies and scenarios for deep lakes and reservoirs.<br>Der Klimawandel beeinflusst Seeökosysteme vielfältig durch direkte und indirekte Temperatureffekte auf die hydrophysikalische Struktur, die Hydrologie, chemische Kreisläufe und biologische Interaktionen. Die Identifikation von Klimasignalen kann durch Landnutzungs- und weitere Umweltveränderungen überlagert werden. Ziel dieser Arbeit war es, Temperatureffekte von Effekten zu unterscheiden, die durch Gewässermanagement oder anderen Umweltveränderungen verursacht werden. Weiterhin sollten komplexe Prozesse verstanden werden, die zu signifikanten Veränderungen in Seeökosystemen führen. Dieses Verständnis ist für Talsperren- und Gewässermanager von besonderer Bedeutung, um ungewünschten Folgen des Klimawandels entgegenwirken zu können.
Für die Studie wurden Langzeitdaten für meteorologische, hydrophysikalische und biologische Variablen (Phytoplankton, Crustaceen-Zooplankton, Fischbesatz) der Talsperre Saidenbach ausgewertet. Mehrere Indikatoren für die Auswirkungen des Klimawandels konnten basierend auf diesen Daten identifiziert werden. Diese gehören insbesondere eine Erhöhung der Wassertemperatur seit 1975, zeitigere Eisaufbrüche und eine veränderte Schichtungsstruktur. Dabei wurde im Sommer die Schichtungsstabilität höher und die Intensität der Durchmischung geringer. Das Wasser in der Talsperre erwärmte sich stärker als die Zuflüsse, wodurch diese sich zunehmend tiefer und unterhalb der Thermokline einschichten.
Eine zunehmende jährliche Phytoplanktonbiomasse und Artenwechsel innerhalb der Planktongemeinschaft sind weitere Indikatoren für Klimafolgen. Die Kieselalge Aulacoseira subarctica erlangte in Jahren mit warmen Wintern und zeitigen Eisaufbrüchen eine Dominanz während der Frühjahrsentwicklung. Das ungewöhnliche Auftreten dieser Art in aphotischen Tiefen konnte durch eine leichtere Resuspension im Vergleich zu anderen Kieselalgen erklärt werden. Durch zeitige Resuspension gleich nach Eisaufbruch kann A. subarctica ein hohes Inokulum etablieren. Trotz reduzierter Nährstoffzufuhr ins Epilimnion wurde im Sommer die Kieselalge Fragilaria crotonensis vermehrt durch Cyanobakterien verdrängt, was jedoch gut mit den Änderungen der hydrophysikalischen Struktur erklärt werden kann.
Obwohl seit 1990 insgesamt mehr Phytoplankton zur Verfügung steht konnte das Crustaceen- Zooplankton in der Talsperre Saidenbach nicht von diesen verbesserten Nahrungsbedingungen profitieren. Die Daphnia-Abundanzen waren seit 1990 stark verringert. Es konnte gezeigt werden, dass der Einfluss des Fischbesatzes unterschätzt wurde und die künstlich ins System eingebrachten Silberkarpfen zeitweise bis zu 70% der zooplanktivoren Fischbiomasse ausgemacht haben. Zoo- planktivore Fische haben einen temperatur- und dichteabhängigen Effekt auf das Zooplankton. Das schnellere Populationswachstum von Daphnia kann bei hohem Besatz mit zooplanktivoren Fischen nicht die erhöhte Fraßaktivität der Fische ausgleichen. Dennoch konnte Temperatur als der wichtigste Einflussfaktor auf die Phänologie des Zooplanktons identifiziert werden, gefolgt von zooplanktivorem Fisch und Nährstoffzufuhr.
Die Wichtigkeit von submersen Makrophyten in Flachseen ist gut untersucht. Um den Einfluss von Makropyhten auf die Wasserqualität während des Klimawandels auch in tiefen Seen abschätzen zu können, wurde ein komplexes Seemodell entwickelt. Die Simulationen zeigen, dass sich Makrophyten hauptsächlich positiv auf die Wassergüte auswirken und zur Reduktion von Phytoplankton, insbesondere von Cyanobakterien im Sommer, beitragen. In einem 11 m tiefen See betrug die Reduktion 50 %, in 100 m tiefen oligotrophen Seen immer noch 15 %. Die Konkurrenz um Nährstoffe mit dem Phytoplankton war dabei die ursächliche Makrophyten-Plankton-Interaktion. Submerse Makrophyten könnten für die Restaurierung von tiefen Seen folglich genauso wichtig sein, wie für Flachseen. Das komplette Seemodell enthält hydrophysikalische und ökologische Module und ermöglicht damit weitere umfassende Simulationen zur Untersuchung der Auswirkungen des Klimawandels und zur Evaluation von Adaptionsstrategien für Seen und Talsperren.
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ŠRÁMEK, Pavel. "Hodnocení stability rybničního ekosystému v Národní přírodní rezervaci Řežabinec." Master's thesis, 2014. http://www.nusl.cz/ntk/nusl-181009.
Texte intégralRésumé :
The first part is characterized by a pond ecosystem and National Nature Reserve Řežabinec in terms of its historical development and creation. Are mentioned methods , the method and system of protection of the site. The paper describes a method of fish farming during the period of the individual plans of care farming in the last five years and the water conditions in the area . The ecosystem is assessed on the basis of available data in the literature to me In our own work we focus on monitoring water chemistry and state recovery tank , especially in terms of development and biomass of zooplankton species representation in the course of one growing season. He also details the fishing and agricultural management and water management conditions in the locality. Marginally judging submerged and littoral vegetation and the presence of water birds. This work demonstrated the dependence of the size of the fish stock on the frequency of a generic representation of zooplankton and the positive impact of lower stocking on the development and stability of the entire ecosystem. Contributes to the stability and sensitive farming in the last period.