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Articoli di riviste sul tema "Intertidal organisms – South Africa"
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Altuna, Alvaro. "Bathymetric distribution patterns and biodiversity of benthic Medusozoa (Cnidaria) in the Bay of Biscay (north-eastern Atlantic)". Journal of the Marine Biological Association of the United Kingdom 87, n. 3 (16 maggio 2007): 681–94. http://dx.doi.org/10.1017/s0025315407055920.
Testo completoAbstract (sommario):
Bathymetric distribution data were compiled on benthic Medusozoa (Cnidaria) of the Bay of Biscay and nearby seas. The area of study extended from 42°N to 48°30′N, and westwards to 10°W. The depth range of each species was traced in a review of the literature. The number of species in each of several depth zones is summarized here: intertidal, intertidal–30 m, 30–100 m, and thereafter at 100 m depth intervals throughout the entire column (0–5000 m). Some 200 species were included (six Scyphozoa, four Staurozoa, 190 Hydrozoa). Of these, 196 could be ascribed to the Coastal Realm (0–200 m) (118 exclusives; 60% of the fauna) and Deep Benthic Realm (200+m) (31 exclusives;16%), with 47 species inhabiting both (24%). Eighty-eight species (45%) were present intertidally. Biodiversity was highest above the summer thermocline (30 m) (133 species, 67%), and no species have been recorded from depths greater than 4706 m. Beyond the thermocline, biodiversity dropped with increasing depth. A significant change occurred in the 30–100 m interval (123 to 78 species; Distinctiveness=51%), although all intervals down to the 300 m isobath exhibited substantial changes. Most species in the Deep Benthic Realm thrive on the upper part of the slope (200–800 m; 50 species). Biodiversity appeared homogeneous across wide bathymetric ranges in deep bathyal and abyssal regions, perhaps due to unique vertical biocenological units. Thus, 15 species are known between 1400 and 2000 m, and four between 3100 and 4300 m. Fifty-four species were considered eurybathic (34%), with some showing impressive bathymetric ranges of over 4000 m, but most species were stenobathic (106, 66%).As with data on benthic medusozoans from South Africa, the north-western Atlantic, the Arctic, and the warm western Atlantic (Bermuda), bathymetric biodiversity was highest in the first 100 m, with a substantial drop below that in species numbers on the shelf and at the beginning of the bathyal. While numbers of species may vary widely from one geographical region to another, such variations are due to differences in biodiversity in the upper 100 m. Hydroid species richness in the deep bathyal and abyssal is similar and always low. Worldwide, benthic medusozoan biodiversity is highest at shallow depths, and these organisms normally seem to be minor components of deep benthos. Very likely, the graph of biodiversity at increasing depth is similar worldwide for the Hydrozoa.
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Tychsen, John, Ole Geertz-Hansen e Jesper Kofoed. "KenSea – development of an environmental sensitivity atlas for coastal areas of Kenya". Geological Survey of Denmark and Greenland (GEUS) Bulletin 10 (29 novembre 2006): 65–70. http://dx.doi.org/10.34194/geusb.v10.4912.
Testo completoAbstract (sommario):
The Kenya coastline extends 600 km from the border of Tanzania in the south to the border of Somalia in the north (Fig. 1). The Kenyan coast features a diverse marine environment, including estuaries, mangroves, sea grass beds and intertidal reef platforms and coral reefs, which are vital for the reproduction of marine organisms. These coastal ecosystems are regarded as some of the most valuable in Kenya but face serious threats from the ever increasing human pressure of tourism, industrial pollution, destructive fishing, mangrove logging and other unsustainable uses of marine resources. Another serious threat is the maritime transportation activities along the coast and at the ports. It is estimated that at any given time more than 50 ships operate in the major shipping lanes off the Kenyan coast, of which about nine are oil tankers with capacities ranging from 50 000 to 250 000 tonnes. Furthermore, the harbour of Mombasa serves as the major port for countries in East Africa. In recognition of the risks posed by oil pollution the government of Kenya and the commercial petroleum industry agreed to develop a National Oil Spill Response Contingency Plan (NOSRCP) with the purpose of enabling a speedy and effective response to any oil spill within the territorial waters of Kenya. An important element of this plan was the mapping of the coastal resources and the development of an environmental sensitivity atlas showing the vulnerability of the coast to marine oil spills. In 2004, the Government of Kenya approached the United Nations Development Program (UNDP) in Kenya for financial support to develop an environmental sensitivity atlas. The project was approved and forwarded for funding by the Danish Consultancy Trust Fund administrated by United Nations Operational Program (UNOPS) in Copenhagen. The project was announced in Denmark, and the KenSea group headed by the Geological Survey of Denmark and Greenland (GEUS) was awarded the contract. The project comprises four phases: (1) data compilation and development of the KenSea database, (2) development of a coastal classification for Kenya, (3) development of the sensitivity index jointly with a group of stakeholders, and (4) compilation of the KenSea environmental sensitivity atlas (Tychsen 2006).
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Reinecke, Koot, Werner Schoeman e Sophié Reinecke. "Cellular biomarker responses of limpets (Mollusca) as measure of sensitivity to cadmiumcontamination". Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie 27, n. 2 (16 settembre 2008): 123–42. http://dx.doi.org/10.4102/satnt.v27i2.86.
Testo completoAbstract (sommario):
Due to the availability and chemical nature of some heavy metals, sub-lethal toxicant levels may persist in the ocean waters and may cause physiological problems and toxicity in invertebrates and other marine organisms. Although studies of metal concentrations in False Bay showed relatively low mean concentrations of Cd, invertebrates such as molluscs, crustaceans and many other groups are able to accumulate high levels of heavy metals in their tissues and still survive in the heaviest polluted areas. They can accumulate numerous pollutants from natural waters in quantities that are many orders of magnitude higher than background levels. Bioaccumulation ofcadmium in intertidal species could cause stress which may be measurable at the cellular level. A variety of limpet species that may serve as suitable ecotoxicological monitoring species occur in abundance on rocky shores along the South African coastline. The aim of this study was to obtain sensitivity data which could contribute to the selection of a suitable monitoring species and the eventual establishment of a species sensitivity distribution model (SSD) with a biomarker responseas endpoint. The limpets Cymbula oculus, Scutellastra longicosta, Cymbula granatina and Scutellastragranularis as well as water samples were collected at two localities in False Bay, South Africa. Analysis of water and biological samples were done by atomic absorption spectrometry. Exposures were done to three different sublethal concentrations of cadmium in the laboratory in static flow tanks over three days. There was a moderate increase in cadmium body concentrations over time. Results obtained at three exposure concentrations showed no significant differences in metal concentrations between the different C. oculus samples. Significant differences were obtained between the control and the exposure groups for each exposure time except between the control and the 1mg/L CdCl2 exposure group after 24 and 72 hours of exposure. Cd body concentrations(soft tissue) varied between 4.56 and 21.41µg/g (wet mass).Mean Cd concentrations in soft tissue of S. longicosta was considerably lower (varying between 1.18 and 19.58 µg/g Cd ) than in the tissues of C. oculus. The control group differed significantly from the 0.8 and 1 mg/L CdCl2 exposures after 48 and 72 hours. Mean Cd body concentrations in S. granular is were the highest of all exposed species, reaching a level of 148 µg/g Cd at the highest exposure concentration and differed significantly from the means of the other samples of the 0.8 mg/L CdCl2 exposure group after 72 hours and from the 1 mg/L CdCl2 group after 24 hours. Significant differences were also obtained between theCd body concentrations of C. granatina for the three exposure concentrations and three exposure times. Lysosomal membrane integrity was determined for both exposed and control animals, using the neutral red retention assay. Three of the four species showed a significant decrease in retention times with an increase in Cd concentration. Inter-species differences in sensitivity to environmentally relevant cadmium concentrations were reflected in the biomarker responses. Based on reduction of NRR times, the order of relative sensitivity to cadmium was S. granularis >C. oculus> S. longicosta.> C.granatina.
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Oosthuizen, A., e M. J. Smale. "Population biology of Octopus vulgaris on the temperate south-eastern coast of South Africa". Journal of the Marine Biological Association of the United Kingdom 83, n. 3 (9 aprile 2003): 535–41. http://dx.doi.org/10.1017/s0025315403007458h.
Testo completoAbstract (sommario):
Population structure and biology of Octopus vulgaris was investigated along the south-eastern coast of South Africa. Samples were collected inter- and sub-tidally as a precursor to the establishment of an experimental octopus fishery in the region. In total, 300 (intertidal) and 147 (subtidal) O. vulgaris were collected over a two year period. Females were found to dominate the intertidal area (sex ratio 2:1), while no difference was found subtidally (sex ratio 1:1). Of those collected intertidally, immature females were most prevalent while males ranged from immature to mature. Mature females were only found subtidally. A marked size difference was apparent, with the subtidal octopus being substantially larger. Although brooding females were found throughout the year, numbers peaked in summer. Individual fecundity ranged between 42,000–790,000 eggs. The total number of eggs produced and the number of eggs per egg string were correlated to female size. Diet did not vary greatly between the inter- and sub-tidal areas, with the main prey items being crustaceans, teleosts and octopus. It appears that the immature females use the intertidal area to feed and grow, before migrating to deeper areas to mature and spawn.
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HADFIELD, KERRY A., NICO J. SMIT e ANNEMARIÉ AVENANT-OLDEWAGE. "Gnathia pilosus sp. nov. (Crustacea, Isopoda, Gnathiidae) from the East Coast of South Africa". Zootaxa 1894, n. 1 (8 ottobre 2008): 23–41. http://dx.doi.org/10.11646/zootaxa.1894.1.2.
Testo completoAbstract (sommario):
The larvae of gnathiid isopods are known to parasitise a large variety of intertidal fish worldwide. In South Africa, the larvae of Gnathia africana Barnard, 1914, have been recorded from various intertidal fish hosts along the cold West and South Coasts. The warmer East Coast, however, has not previously been sampled for gnathiids. From March 2006 to February 2007, intertidal fishes were collected on the East Coast using hand held nets and kept in aerated tanks until the gnathiids completed their feeding. Once fed, the gnathiids were kept alive in 50 ml bottles with fresh sea water till moulting occurred. Results indicated that all the East Coast intertidal gnathiids were from the same species and new to science, and subsequently described as Gnathia pilosus sp. nov. The G. pilosus male and female can be clearly distinguished from other South African species in having numerous tubercles and setae covering the cephalosome and pereon which are not as pronounced in the other species. The G. pilosus larva can also be distinguished from the other South African species by the triangular-shaped cephalosome and numerous sensory pits covering the body.
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Kruger, Lisa M., e Charles L. Griffiths. "Sources of nutrition in intertidal sea anemones from the south-western Cape, South Africa". South African Journal of Zoology 31, n. 3 (gennaio 1996): 110–19. http://dx.doi.org/10.1080/02541858.1996.11448402.
Testo completo
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Sink, KJ, GM Branch e JM Harris. "Biogeographic patterns in rocky intertidal communities in KwaZulu-Natal, South Africa". African Journal of Marine Science 27, n. 1 (gennaio 2005): 81–96. http://dx.doi.org/10.2989/18142320509504070.
Testo completo
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Prochazka, K. "The reproductive biology of intertidal klipfish (Perciformes: Clinidae) in South Africa". South African Journal of Zoology 29, n. 4 (gennaio 1994): 244–51. http://dx.doi.org/10.1080/02541858.1994.11448358.
Testo completo
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Bremec, Claudia, Cecilia Carcedo, M. Cintia Piccolo, Eder dos Santos e Sandra Fiori. "Sabellaria nanella(Sabellariidae): from solitary subtidal to intertidal reef-building worm at Monte Hermoso, Argentina (39°S, south-west Atlantic)". Journal of the Marine Biological Association of the United Kingdom 93, n. 1 (4 settembre 2012): 81–86. http://dx.doi.org/10.1017/s0025315412000550.
Testo completoAbstract (sommario):
This contribution reports the first record of intertidal reefs built by the sabellariid wormSabellaria nanellain the lower intertidal at Monte Hermoso beach, Argentina (39°S). All previous records ofS. nanellain the study area correspond to solitary individuals from shallow subtidal depths in coastal environments, while the present findings refer to well established reefs on stony rocks. Worms sort medium size sand grains to build the reefs, which contain higher amount of organic matter than the surrounding sediments. Size structure of worms shows multiple size cohorts that include recent recruits and mature adults. Many invertebrates, i.e. various annelids, arthropods, molluscs, nemerteans and nematodes, are the frequent organisms living within the reef, some of them already recorded in the area. The presence of intertidal reefs ofS. nanellaindicates that the species has plasticity to adapt to environments with different physical conditions (subtidal–intertidal areas).
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Boland, J. M. "The horizontal zonation of two species of intertidal barnacle in South Africa". South African Journal of Marine Science 18, n. 1 (giugno 1997): 49–61. http://dx.doi.org/10.2989/025776197784161081.
Testo completoTesi sul tema "Intertidal organisms – South Africa"
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Mostert, Bruce Petrus. "Responses of intertidal macroalgae and associated fauna to interactive processes acting over multiple spatial scales". Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1013370.
Testo completoAbstract (sommario):
The decrease of biological diversity from low latitudes near the equator towards high latitudes is one of the most fundamental patterns noted in ecology. These trends have been the subject of numerous terrestrial and marine studies and have caused the proposal of several explanatory hypotheses. No single hypothesis has adequately accounted for these observed trends. Furthermore, large-scale patterns are frequently modified by processes acting at meso- to small-scales. It is imperative to understand the interaction of these processes to elucidate the mechanisms controlling the structure of intertidal assemblages. The main aim of this thesis was to test the influence of multiple processes at a range of spatial scales on biogenic engineers. Biogenic engineers, such as macroalgae, have been reported to be strongly influenced by processes such as grazing, biogeography and upwelling and subsequent effects are expected to be linked to their associated assemblages. I used infaunal assemblages associated with macroalgae as a model system to understand the interactive effects of meso-scale upwelling in conjunction with large-scale factors (regional and biogeographic). Three species of macroalgae, Hypnea spicifera, Champia lumbricalis and Bifurcaria brassicaeformis, inhabiting different but overlapping home ranges were used in this study. Smaller scale, physical attributes and the associated fauna of these algal species were compared. The effects of meso- to large-scale physical gradients on marine organisms have been investigated in many instances and resultant gradients in physical variables observed. This study was undertaken to investigate morphological trends exhibited by Hypnea spicifera and Champia lumbricalis to compare possible similarities between coastlines and to determine if inferred meso- to large-scale processes influence physical trends in a similar manner despite the coastlines being affected by different hydrodynamic processes. The macroalgae were located in two distinctly different upwelling regimes, Hypnea spicifera on the east and south coasts and Champia lumbricalis on the west coast. Upwelling (delivery of nutrients and primary production) was not found to be an important factor in determining the physical characteristics of macroalgae but there were clear patterns linked to latitude. Mean percentage cover of Hypnea spicifera was positively correlated with distance along the east and south coasts. Mean mass and mean surface area of H. spicifera were, however, negatively correlated with distance from Port St Johns. Mean frond length showed a negative trend but this relationship was not statistically significant. On the west coast, there was a significant increase in mean frond length from north to south for Champia lumbricalis. Mean surface area and mean mass of C. lumbricalis exhibited non-significant negative trends from north to south while there was a non-significant positive trend for mean percentage cover. Following the “Productivity Hypothesis”, these patterns from north to south along the coastlines of South Africa could have important implications for biodiversity associated with these algae. Many previous studies have focussed on the effects of upwelling on species (i.e. effects of nutrients and temperature) but have failed to separate this effect from large scale effects such as biogeography and latitudinal gradients. I tested the influence meso-scale upwelling, large-scale biogeographic processes and latitudinal gradients with two different species of macroalgae one on the east and south coasts of South Africa and the other on the west coast. Hypnea spicifera inhabits the east and south coasts of South Africa spanning two biogeographic provinces and is generally affected by relatively weak upwelling, whereas Champia lumbricalis inhabits the west coast spanning one biogeographic province which is subjected to intense persistent upwelling year round. Within the east and west coast biogeographic provinces there are, however, regions with both upwelling and non-upwelling. On the east and south coasts, entire assemblages differed significantly among the three Regions (St Lucia, Port Alfred and Knysna, while assemblages between upwelling/non-upwelling areas were not different. Assemblages on the different shores differed significantly from each other. There were no significant effects of region or upwelling for the number of individuals of Crustacea or Polychaeta, while Mollusca showed a significant effect of region. The number of individuals of other taxa showed a significant interaction of region and upwelling. Region had a significant effect on number of species of molluscs and other taxa, while there was no effect for either region or upwelling for the Crustacea or Polychaeta. In general different factors were shown to be important (region and shore) while upwelling was rarely important. On the west coast assemblages associated with C. lumbricalis were not influenced by region or upwelling but there were significant differences between shores. Region, upwelling ad shore did not affect number of individuals. There was a significant interaction of region and upwelling for the number of species of crustaceans, while numbers of species of Mollusca, Polychaeta and other taxa showed no effects. In general, regional factors strongly influenced most organisms, while upwelling played a minor role. Hypotheses about differences between upwelling and non-upwelling regions in terms of species abundances and composition due to the input of cold nutrient rich water were not supported. A link between the effects of larger-scale biogeographic factors and their influence on habitat forming taxa and the resultant effects on associated infauna would be a likely explanation for the patterns observed in this study. Diversity of assemblages is known to be influenced by the structural complexity of a habitat, increasing complexity increases the amount of available niches therefore potentially increasing the number of species found within that habitat. Three species of macroalgae, Hypnea spicifera, Champia lumbricalis and Bifurcaria brassicaeformis were selected on the basis of being structurally similar and having their distributional ranges overlap in order to elucidate the effects of structure and macroalgal species on associated assemblages. Hypnea spicifera is different in terms of surface area and biomass from Champia lumbricalis and Bifurcaria brassicaeformis. Assemblages of species found on the three rhodophytes showed both shore and the species of alga had significant effects on composition. Only numbers of individuals of molluscs were affected by the species of alga. Crustacea and Polychaeta showed an interaction of the species of alga with shore. In the case of this study, it is likely that the three species of macroalgae mitigate biological stressors such as predation and physical stressors such as wave exposure and desiccation. In general, meso-scale upwelling is suggested to be marginalised when considering the structuring of assemblages associated with macroalgae, while large scale biogeography has more of an influence. Within shores, assemblages were also strongly influenced by smaller-scale factors such as differences in the structure and species of alga. This study indicates the importance of investigating patterns across a range of spatial scales to gain a comprehensive understanding of factors influencing intertidal organisms.
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Ndhlovu, Rachel Tintswalo. "Temporal variability in the fatty acid composition of suspension-feeders and grazers on a South African rocky shore". Thesis, Rhodes University, 2014. http://hdl.handle.net/10962/d1020879.
Testo completoAbstract (sommario):
Numerous ecological studies have used lipids to determine trophic pathways in aquatic systems, as fatty acid profiles provide time-integrated information on an organism’s assimilated diet. Many of these studies have, however, been based on sample collections with a limited temporal scale. The trophic ecology of pelagic systems has been studied intensively using fatty acid analyses, but very little work has been directed toward benthic communities, with the intertidal being especially neglected. The investigation of trophic pathways within rocky shore communities will help us to better understand system responses to environmental changes. The determination of long term temporal variation of the food web within a community could reveal the type, magnitude, duration and frequency of highly seasonal productivity. Changes in fatty acid profiles through time in primary consumers of intertidal rocky shores are poorly understood, but represent an important step towards a more comprehensive understanding of rocky shore food webs, compared with those derived from snapshot or short-term studies. The aim of this thesis was to clarify the temporal variability in the diets of rocky shore intertidal suspension-feeders (the brown mussels Perna perna and the Cape reef worm, Gunnarea gaimardi) and grazers (the Cape sea urchin Parencinus angulosus and the Goat-eye limpet, Cymbulus oculus) on the south east coast of South Africa using fatty acid profiles, and to investigate the effects of life style (e.g. feeding mode) and life cycle on temporal variations in tissue fatty acid profiles. I had three hypotheses: firstly, that suspension-feeders experience high levels of variability in their diets through time because water quality has the potential to change quickly and drastically, whereas grazers experience less variability in their diets over time since their food sources are more constant. Secondly, the reproductive cycles of the suspension-feeder P. perna and the grazer P. angulosus affect the fatty acid composition of their gonads, with temporal variations in lipid composition reflecting changes in reproduction investment. Thirdly, the total amount of energetic reserves available for reproduction are different for each gender (females allocate more energy to egg production than males allocate to gamete production). To address these aims, fatty acid profiles of suspension-feeders and grazers were investigated over a period of twelve months (from July 2010 to June 2011) at a single site on the south east coast of South Africa. The results showed high variability in the fatty acid composition of both the suspension-feeders strongly related with changes in their food source (suspended particulate material). Furthermore, similar temporal changes in fatty acid profiles of the two suspension-feeders were observed over time, reflecting their common diet and life style. There were some inter-specific differences in the suspension-feeders, likely originating from differences in their particle capturing mechanisms. Grazers showed less variability through time compared with the suspension-feeders, with the limpets being more consistent than the sea urchins. The temporal variability in the sea urchin diets may have resulted from the highly diverse and heterogeneous food sources available to them, whereas limpets may be more selective and have a limited range of diet items. Differences between the two grazer species may have arose from differences in their feeding strategies and intertidal zonation. The fatty acid compositions of gonad tissues in both P. perna and P. angulosus showed temporal variability strongly related to reproductive cycle. Differences in the fatty acid values between females and males were apparent, with females richer in total and polyunsaturated fatty acids than males. Spawning and gametogenesis influenced the variability of fatty acids through time in both species, suggesting the importance of considering the reproductive cycle when studying lipids in rocky shore species. Little evidence of lipid transfer between muscles and gonads was seen, suggesting the importance of direct lipid storage into the reproductive tissues. The influence of diet and life history of intertidal consumers on the temporal variability of their fatty acid compositions is important to understand, as it provides us with a better understanding of the functioning of rocky shore systems. There is an enormous potential for future research in this field of study.
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Bownes, Sarah. "Habitat segregation in competing species of intertidal mussels in South Africa". Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1005392.
Testo completoAbstract (sommario):
Mytilus galloprovincialis is invasive on rocky shores on the west coast of South Africa where it has become the dominant intertidal mussel. The success of this species on the west coast and its superior competitive abilities, have led to concern that it may become invasive on the south coast at the expense of the indigenous mussel Perna perna. On shores where these species co-occur, there appears to be habitat segregation among zones occupied by mussels. M.galloprovincialis dominates the high-shore and P.perna the low-shore, with a mixed zone at mid-shore level. This study examined the factors responsible for these differences in distribution and abundance. The study was conducted in Plettenberg Bay and Tsitsikamma (70km apart) on the south coast of South Africa. Each site included two randomly selected locations (300-400m apart). A third mussel species, Choromytilus meridionalis, is found in large numbers at the sand/rock interface at one location in Plettenberg Bay. Aspects of settlement, recruitment, growth and mortality of juvenile and adult mussels were examined at different tidal heights at each site. Quantitative analysis of mussel population structure at these sites supported the initial observation of vertical habitat segregation. Post-larvae were identified to species and this was confirmed using hinge morphology and mitochondrial DNA analysis. Size at settlement was determined for each species to differentiate between primary and secondary settlement. Adult distribution of C.meridionalis was primarily determined by settlement, which was highly selective in this species. Settlement, recruitment and growth of P.perna decreased with increasing tidal height, while post-settlement mortality and adult mortality increased higher upshore. Thus all aspects of P.perna’s life history contribute to the adult distribution of this species. Presumably, the abundance of P.perna on the high-shore is initially limited by recruitment while those that survive remain prone to elimination throughout adulthood. M.galloprovincialis displayed the same patterns of settlement and recruitment as P.perna. However, post-settlement mortality in this species was consistently low in the low and high zones. Juvenile growth also decreased upshore, suggesting that M.galloprovincialis may be able to maintain high densities on the high-shore through the persistence of successive settlements of slow-growing individuals. The low cover of M.galloprovincialis on the lowshore appeared to be determined by adult interactions. M.galloprovincialis experienced significantly higher adult mortality rates than P.perna in this zone. There were seasonal variations in the competitive advantages enjoyed by each species through growth, recruitment or mortality on the low-shore. In summer, P.perna had higher recruitment rates, faster growth and lower mortality rates, while M.galloprovincialis had slightly higher recruitment rates and faster growth rates in winter. P.perna is a warm water species while M.galloprovincialis thrives on the cold-temperate west coast of South Africa. Therefore both species appear to be at the edge of their optimal temperature regimes on the south coast, which may explain the seasonal advantages of each. Nevertheless, P.perna has maintained spatial dominance on the low-shore suggesting that it may ultimately be the winner in competition between these species. M.galloprovincialis appears to have a refuge from competition with P.perna on the high-shore due to its greater tolerance of desiccation stress, while being competitively excluded from the low-shore. Warm water temperatures coupled with poor recruitment rates at most sites may limit the success of M.galloprovincialis on this coast.
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Bosman, Alison L. "Avian determinants of rocky intertidal community structure in South Africa". Doctoral thesis, University of Cape Town, 1987. http://hdl.handle.net/11427/8407.
Testo completoAbstract (sommario):
Includes bibliographies.Rocky islands in Saldanha Bay, southwestern Cape, South Africa, support aggregations of seabirds. Guano produced by the seabirds washed off the islands into intertidal and nearshore waters,where it provides a source of inorganic and organic nutrients. The concentrations of nutrients in intertidal rockpools at island and mainland sites in the Saldanha Bay area were measured,and the biological structures of intertidal communities at these sites were compared in the light of differences in intertidal nutrient status. Monthly measurements were made of algal production and of the growth, density, reproductive condition and mortality of the dominant intertidal herbivore, Patella granularis.The rate of intertidal algal production was enhanced on shores washed by nutrient-rich waters, and the growth rates and life-history patterns of populations of P. granularis were, in turn, modified by the increased availability of algal food. On unenriched shores rates of algal production and limpet growth and reproduction were slow. Seabirds thus influence trophic relationships between intertidal organisms, without themselves being components of the community. Islands in Saldanha Bay also support dense populations of African Black Oystercatchers Haematopus moqu.ini, which forage intertidally. Predation by oystercatchers on P. granular is resulted in a modification of limpet densities and population size structures, and a reduction in the intensity of grazing. The impact of predation was, however, modified by the presence, in intertidal waters, of nutrients from seabird guano, and the consequences thereof. It is proposed that differences in the structures of communities on rocky shores, and in the roles of processes influencing structure, might •be due, in part, to differences in the nutrient status of intertidal waters.
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Bownes, Sarah. "Habitat segregation in competing species of intertidal mussels in South Africa". Connect to this title online, 2005. http://eprints.ru.ac.za/238/.
Testo completo
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Zardi, G. I. "A genetic and ecophysiological comparison of co-occuring indigenous (Perna perna) and invasive (Mytilus galloprovincialis) intertidal mussels". Thesis, Rhodes University, 2006. http://hdl.handle.net/10962/d1003066.
Testo completoAbstract (sommario):
The Mediterranean mussel Mytilus galloprovincialis is the most successful marine invasive species in South Africa. Its presence has had significant ecological consequences on the intertidal communities of the west coast. On the south coast, M galloprovincialis co-exists and competes with the indigenous intertidal mussel Perna perna in the lower balanoid zone, where they show partial habitat segregation. The upper and the lower mussel zones are dominated by M. galloprovincialis and P. perna respectively while they co-occur in the mid zone. In this thesis M. galloprovincialis and P. perna are compared in terms of their population genetics and their ecophysiology. The success of an invader depends on its ability to react to new environmental factors, especially when compared to indigenous species. The distribution and diversity of intertidal species throughout the world are strongly influenced by periodic sand inundation and hydrodynamic stress. Occupying the lower intertidal zone, P. perna is more strongly influenced by sand (burial and sand in suspension) than M. galioprovincialis. Despite this, P. perna is more vulnerable to the effects of sand, showing higher mortality rates under experimental conditions in both the laboratory and the field. M. galioprovincialis has longer labial palps than P. perna, indicating a better ability to sort particles. This, and a higher tolerance to anoxia, explains its lower mortality rates when exposed to burial or suspended sand. Habitat segregation is often explained by physiological tolerances, but in this case, such explanations fail. The ability of a mussel to withstand wave-generated hydrodynamic stress depends mainly on its byssal attachment strength. The higher attachment strength of P. perna compared to M. galioprovincialis and of solitary mussels compared to mussels living within a bed (bed mussels) can be explained by more and thicker byssal threads. M galloprovincialis also has a wider shell, is subjected to higher hydrodynamic loads than P. perna and shows a higher theoretical probability of dislodgement, this is borne out under field conditions. The attachment strength of both species increased from higher to lower shore, in parallel to a gradient of a stronger wave action. Monthly measurements showed that P. perna is always more strongly attached than M. galloprovincialis and revealed seasonal fluctuations of attachment strength for both species in response to wave height. The gonad index of both species was negatively cross-correlated with attachment strength. The results are discussed in the context of the evolutionary strategy of the alien mussel, which directs most of its energy to fast growth and high reproductive output, apparently at the cost of reduced attachment strength. This raises the prediction that its invasive impact will be more pronounced at sites subjected to low or moderate wave action at heavily exposed sites. The potential of a species for invasion is also determined by the ability of the invader to disperse. Population genetics provide indirect information about dispersal through a direct measurement of gene flow. The low genetic divergence (measured as mtDNA) of M. galloprovincialis confirms its recent arrival in South Africa. In contrast, the population genetics structure of P. perna revealed strong divergence on the south-east coast, resulting in a western lineage (straddling the distributional gap of the Benguela System), and an eastern lineage, with an overlap region of the two on the south coast between Kenton-on-Sea and Haga Haga. This genetic disjunction may be caused by Agulhas Current acting as an oceanographic barrier to larval dispersal, or by different environmental selective forces acting on regional populations. Over the last ten years, M. galloprovincialis has shown a decrease or cessation of its spread to the east in exactly the region of the genetic disjunction in P. perna, again suggesting either an oceanographic barrier to larval dispersal, or increasing selection driven by sharp gradients in environmental conditions.
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Mmonwa, Lucas Kolobe. "Phylogeography and epifauna of two intertidal seaweeds on the coast of South Africa". Thesis, Rhodes University, 2009. http://eprints.ru.ac.za/1583/.
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Whittington-Jones, Kevin John. "Ecological interactions on a rocky shore : the control of macroalgal distribution by intertidal grazers". Thesis, Rhodes University, 1998. http://hdl.handle.net/10962/d1005350.
Testo completoAbstract (sommario):
The aim of the present study was to determine the potential impact of intertidal grazers on the distribution of macro algae on the south coast of South Africa. Particular attention was paid to the large patellid limpet, Patella oculus, which is found thoughout the intertidal zone. Studies of gut contents revealed that Patella oculus was capable of ingesting not only the thallus of foliose (eg. Ulva spp.) and encrusting coralline macroalgae, but also spores and diatoms. The inclusion of these relatively small particles in the diet was surprising, as electron micrographs of the radula of P.oculus revealed that it is typically docoglossan in structure. Such radulae are thought to be poorly suited for collecting small food particles. Sand made up a significantly higher proportion of the gut contents than other particles at all shore heights, which suggests that P.oculus might be capable of excavating the rocky substratum, or of sweeping up sand, while searching for food. Analysis of the gut contents of other local herbivorous molluscs, was also carried out. These species included the winkles, Oxystele variegata and O.sinensis, and the small pulmonate limpets, Siphonaria concinna, S.capensis, and S.serrata. The guts of all species contained mainly spores and diatoms, although small fragments of Ulva sp. were found. The population structure of Patella oculus was investigated at two sites, Cannon Rocks and Old Woman's River. At Cannon Rocks, mean shell length of low-shore animals was significantly lower than that of both mid- and high-shore animals, while at Old Woman's River, no significant difference was found among shore heights. A regression equation for In (shell length) vs In (dry weight) was calculated, and based on length data, the biomass density (g dry mass.m⁻²) of P.oculus at Old Woman's River was estimated. Values ranged from 2.8 on the low- and midshore to 0.37 on the high-shore. A manipulative field experiment was used to determine the impact of mesograzers and macrograzers (such as Patella oculus) on the distribution of intertidal macro algae on the mid- and low-shore at Old Woman's River. Grazers were excluded using mesh cages (mesh size = 3mm), in two separate experiments, one in winter and the other in spring. Percentage cover of macroalgal species and sessile invertebrates was estimated at approximately 6 week intervals for up to 3 months. MANOV A showed that treatments did not significantly affect cover of macroalgae or barnacles during winter. However, towards the end of the spring experiment (midshore only) cover of barnacles and green foliose turfs did increase in those plots from which mesograzers and/or macro grazers were excluded. The failure of the statistical tests to detect significant differences at some time intervals may have been caused by high levels of variation among replicates. This suggests that factors other than grazing are of overriding importance in determining the distribution of local macroalgae. The existence of a possible symbiotic relationship between Patella oculus and the red foliose alga, Gelidium pristoides, was investigated. The availability of various substratum types, including rock, limpet shells, barnacles etc., and the proportion of the total cover of G.pristoides on each, was calculated. It was shown that a significantly higher proportion of the alga grew on limpet shells, although the availability of this substratum type was low. It is thought that the aggressive behaviour of P.oculus prevents all but juvenile Patella longicosta from grazing on its shell, thus providing a refuge from grazing for G.pristoides.
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Innes, Sheona. "Tropical intertidal seaweed turf communities of Jesser Point, Sodwana Bay, South Africa". Bachelor's thesis, University of Cape Town, 2010. http://hdl.handle.net/11427/26378.
Testo completoAbstract (sommario):
Algal turfs play an important role in both tropical and temperate reef ecology, supporting a diverse array of macrofauna as well as being primary producers within both intertidal and subtidal ecosystems. Biodiversity and biomass patterns of the intertidal algal turfs at Sodwana Bay, South Africa have not yet been established so this study was undertaken to investigate these. It was hypothesised that both biodiversity and biomass would decrease with increasing height along the shore, as well as that sediment would have an effect on the community composition of the turfs. The community was sampled over a vertical range of 1.2 m and found to be dominated by the red alga Jania intermedia (24.21 % of total algal coverage) followed by Tolypiocladia glomerulata (18.05 %), Dictyota sp. (13.39 %), Jania adhaerens (12.32 %) and Sphacelaria tribuloides. (5.83 %). No significant vertical zonation patterns were found, though certain species showed vertical trends such as Asparagopsis taxiformis and Sphacelaria tribuloides, which occurred in greatest biomass lower down on the shore, while Tolypiocladia glomerulata occurred higher up on the shore. Sand was found to affect certain species more than others, with Tolypiocladia glomerulata, Jania adhaerens and Asparagopsis taxiformis occurring in greatest biomass when the amount of sediment found in the quadrat was low, while Sphacelaria tribuloides. showed the opposite pattern and Jania intermedia showed no distinct pattern. Sampling took place over 1.2 m vertical height along the shore at spring low tide therefore covering 60 % of the intertidal zone vertically (maximum tidal range in South Africa is 2 m). It is therefore possible that the turfs are the cause of a decline in zonation by remaining damp and decreasing desiccation gradients vertically along the shore.
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Gusha, Molline Natanah C. "A community–wide trophic structure analysis in intertidal ecosystems on the south coast of South Africa". Thesis, Rhodes University, 2018. http://hdl.handle.net/10962/63312.
Testo completoAbstract (sommario):
Coastal ecosystems are more than microhabitats for marine species. Acting as atmospheric carbon filters, species in coastal environments are directly and/or indirectly associated with transferring organic carbon to species at higher trophic levels. However, the progressing change in global climatic conditions has created the need to assess the consequences of the shifting conditions on both direct and indirect interactions of physical and biological parameters at species and/or community levels. From these perturbations, the effects of biotic homogenization on ecosystem functioning and resilience can also be realised. Herein, I discuss the effects of temperature, nutrients, biotic interactions and habitat characteristics on community dynamics within intertidal rock pool systems on the south coast of South Africa using complementary qualitative and quantitative analytical methods. Seasonality had a significant impact on rock pool species with changes in composition and higher richness in winter than summer. The first two axes of the Canonical Correspondence Analysis (CCA) of the plant and animal communities each explained ~20% of the relationship between physico-chemical parameters and biological variables. The CCA highlighted that seasonal shifts in chlorophyll-a, conductivity, salinity, water depth, surface area and substratum type indirectly influenced species composition. For example, pools with heterogenous substratum comprising a mixture of sand and rock exhibited higher species diversity than homogenously bedded pools. Furthermore, a Bayesian analysis of community structure based on stable isotope ratios was used to assess how trophic pathways of carbon and nitrogen elements reflected community composition and richness. Isotopic biplots showed an increase in food web size, food chain length and the trophic positions of fish and some gastropods in winter compared to summer. There was greater dietary overlap among species in larger pools. In addition, while isotopic nearest neighbour distance and species evenness also showed a positive increase with pool size in summer, the same metrics were almost constant across all pool sizes in winter. These changes in food web packing and species evenness suggest seasonal preferences or migration of species in summer from small pools to larger pools with stable physico-chemical parameters. Furthermore, the presence of fish was seen to promote trophic diversity within some pools. The results from laboratory microcosm grazing experiments demonstrated significant direct and indirect effects of temperature and nutrients within plankton communities. Copepod grazing had an indirect positive influence on phytoplankton biomass and size structure while the interactive effects of temperature and nutrients had contrasting effects on both phytoplankton communities and copepod biomass. Shifts in water chemistry and nutrient treatments were also observed in the presence of copepods. Phosphate addition had a recognisable impact on plankton communities. The presented synthesis of the literature mainly highlighted that positive effects at one trophic level do not always positively cascade into the next trophic level which is evidence of complex interactive biotic, habitat and water chemistry effects within these intertidal ecosystems. Thus, to further understand cascading effects or community structure functioning in general, there may be a need to incorporate and understand species functional traits and how they contribute to trophic diversity, community restructuring and functioning in coastal habitats.
Libri sul tema "Intertidal organisms – South Africa"
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Rodger, Bosch, a cura di. Invaded: The biological invasion of South Africa. Johannesburg: Wits University Press, 2009.
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2
Musil, Charles F. Invasive alien flora and fauna in South Africa: Expertise and bibliography. A cura di Macdonald I. A. W, Germishuizen Gerrit, Du Plessis Emsie e South African National Biodiversity Institute. Pretoria: South African National Biodiversity Institute, 2007.
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3
Pole, Adrian. Public participation in the context of the regulation of genetically modified organisms in South Africa: A study. Pretoria: Dept.: Environmental Affairs and Tourism, 2008.
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4
International Workshop on Campylobacters, Helicobacters and Related Organisms (9th 1997 Cape Towm). Campylobacter,helicobacter and related organisms: Proceedings of the 9th International Workshop held in Cape Town, South Africa, 15-19 September 1997. Cape Town: Institute of Child Health,University of Cape Town, 1998.
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Esler, Karen J., Anna L. Jacobsen e R. Brandon Pratt. The Biology of Mediterranean-Type Ecosystems. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198739135.001.0001.
Testo completoAbstract (sommario):
The world’s mediterranean-type climate regions (including areas within the Mediterranean, South Africa, Australia, California, and Chile) have long been of interest to biologists by virtue of their extraordinary biodiversity and the appearance of evolutionary convergence between these disparate regions. Comparisons between mediterranean-type climate regions have provided important insights into questions at the cutting edge of ecological, ecophysiological and evolutionary research. These regions, dominated by evergreen shrubland communities, contain many rare and endemic species. Their mild climate makes them appealing places to live and visit and this has resulted in numerous threats to the species and communities that occupy them. Threats include a wide range of factors such as habitat loss due to development and agriculture, disturbance, invasive species, and climate change. As a result, they continue to attract far more attention than their limited geographic area might suggest. This book provides a concise but comprehensive introduction to mediterranean-type ecosystems. As with other books in the Biology of Habitats Series, the emphasis in this book is on the organisms that dominate these regions although their management, conservation, and restoration are also considered.
Capitoli di libri sul tema "Intertidal organisms – South Africa"
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Branch, G. M., e C. A. Moreno. "Intertidal and Subtidal Grazers". In Rocky Shores: Exploitation in Chile and South Africa, 75–100. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-78283-1_5.
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Dye, A. H., M. H. Schleyer, G. Lambert e T. A. Lasiak. "Intertidal and Subtidal Filter-Feeders in Southern Africa". In Rocky Shores: Exploitation in Chile and South Africa, 57–74. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-78283-1_4.
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Lastovica, A. J. "Campylobacter/Helicobacter Bacteraemia in Cape Town, South Africa, 1977–1995". In Campylobacters, Helicobacters, and Related Organisms, 475–79. Boston, MA: Springer US, 1996. http://dx.doi.org/10.1007/978-1-4757-9558-5_88.
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Dye, A. H., G. M. Branch, J. C. Castilla e B. A. Bennett. "Biological Options for the Management of the Exploitation of Intertidal and Subtidal Resources". In Rocky Shores: Exploitation in Chile and South Africa, 131–54. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-78283-1_7.
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Odendaal, F. J., M. O. Bergh e G. M. Branch. "Socio-Economic Options for the Management of the Exploitation of Intertidal and Subtidal Resources". In Rocky Shores: Exploitation in Chile and South Africa, 155–67. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-78283-1_8.
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Siegfried, W. R., P. A. R. Hockey e G. M. Branch. "The Exploitation of Intertidal and Subtidal Biotic Resources of Rocky Shores in Chile and South Africa — An Overview". In Rocky Shores: Exploitation in Chile and South Africa, 1–15. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-78283-1_1.
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Foster, G. G., e A. N. Hodgson. "The distribution and reproduction of three sympatric species of intertidal holothurians from South Africa". In Echinoderms through Time, 505. CRC Press, 2020. http://dx.doi.org/10.1201/9781003077831-118.
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Lewis, Matthew C., e M. Justin O’Riain. "The Ecology of Chacma Baboon Foraging in the Marine Intertidal Zone of the Cape Peninsula, South Africa". In Primates in Flooded Habitats, 148–51. Cambridge University Press, 2019. http://dx.doi.org/10.1017/9781316466780.021.
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Adenle, Ademola A., Hans De Steur, Kathleen Hefferon e Justus Wesseler. "Two Decades of GMOs". In Science, Technology, and Innovation for Sustainable Development Goals, 401–22. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780190949501.003.0020.
Testo completoAbstract (sommario):
Agricultural technologies have a key role to play in advancing international development, including achievement of the sustainable development goals (SDGs). Genetically modified organisms (GMOs) are among a wide of range of agricultural technologies that can play a significant role in meeting SDG1 (poverty eradication), SDG2 (zero hunger), SDG13 (climate change), and other interlinked SDGs. Yet GMO opposition persists in Europe with spillover effects in Africa, Asia, South America, and Latin America, thereby limiting the adoption of the new technology in the developing world. This chapter outlines two decades of positive impacts of GMOs in terms of socioeconomic and environmental benefits and considers their potential role in addressing the challenges presented in the 2030 development agenda. The authors highlight fundamental challenges in the application of GMOs, including the overly cautious application of precautionary principle and the lack of an international GMO regulatory framework. Developing countries need to employ risk-assessment models that balance benefits, costs, and risks of GMOs, focusing on local agricultural and environmental practices, rather than following developed countries.
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Bardgett, Richard. "Soil and the Distant Past". In Earth Matters. Oxford University Press, 2016. http://dx.doi.org/10.1093/oso/9780199668564.003.0006.
Testo completoAbstract (sommario):
Rainbow Beach is a small town on the coastal dunes of eastern Australia, near Brisbane. I had travelled there to meet with some colleagues to sample soils from the vast coastal sand dunes that surround the area. It might seem an unusual place to visit to collect soil, but a unique sequence of soils has formed in the sand dunes, which differ greatly in age. As you move inland from the sea, the soils get progressively older and deeper, and more weathered and nutrient-poor. The youngest soils are shallow, having only just started to form in recent sand dunes, whereas the oldest soils are around half a million years old and can reach 25 metres deep. These are among the oldest, deepest, and most weathered soils that I have sampled, and what I recall most vividly is how stunted and sparse the vegetation was that grew there, reflecting their struggle to grow in such ancient, weathered soil. The soils of Rainbow Beach are by no means the oldest on Earth. Hidden beneath ice sheets in Greenland, scientists recently discovered a soil that was 2.7 million years old, a remnant of the fertile tundra that covered the area before the ice sheets came. And scientists working in South Africa recently discovered a soil, now compacted in rock, that is 3 billion years old. One of the most fascinating things about soil is that it is incredibly diverse; soils vary enormously across continents, countries, and from valley to valley and field to field. Even within a small patch of land, such as a field, forest, or vegetable garden, the underlying soil can vary considerably. Over distances of metres, it might differ in its texture and depth, and in its pH, being acid in one patch of a field and neutral in another. Soils also vary greatly in the diversity of living organisms that live within them. I will go into more detail about the diversity of soil life later in this book; but for now suffice to say that it is vast. Soils also change with time.
Atti di convegni sul tema "Intertidal organisms – South Africa"
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Astafieva, M. M., A. Y. Rozanov, D. H. Cornell e R. B. Hoover. "Development of living organisms on the lava-water interface of Palaeoproterozoic Ongeluk lavas of South Africa". In Optical Engineering + Applications, a cura di Richard B. Hoover, Gilbert V. Levin, Alexei Y. Rozanov e Paul C. Davies. SPIE, 2008. http://dx.doi.org/10.1117/12.791901.
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