Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean

 

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dc.contributor.advisor Branch, George M en_ZA
dc.contributor.advisor Sink, Kerry J en_ZA
dc.contributor.advisor Kaehler, Sven en_ZA
dc.contributor.author Porter, Sean N en_ZA
dc.date.accessioned 2014-10-31T18:05:46Z
dc.date.available 2014-10-31T18:05:46Z
dc.date.issued 2009 en_ZA
dc.identifier.citation Porter, S. 2009. Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean. University of Cape Town. en_ZA
dc.identifier.uri http://hdl.handle.net/11427/9018
dc.description Includes bibliographical references (p. 209-274). en_ZA
dc.description.abstract The biogeography and ecology of benthic shallow subtidal reef communities in the western Indian Ocean is poorly known, particularly in north-eastern South Africa and southern Mozambique. This thesis uses quantitative information to resolve biogeographic patterns, define reef community types, elucidate potential abiotic determinants of community composition, and evaluate whether subsidies of riverine-derived particulate organic matter (POM) support filter-feeder biomass and drive biogeographic patterns. A large-scale biogeographic analysis was conducted using quantitative biomass data derived from 55 shallow subtidal reefs spanning five countries in the western Indian Ocean. Two statistically distinct marine provinces, Tropical Indo-West Pacific and Subtropical Natal, were recognised by differences in community composition and separated by a biogeographic break in the vicinity of Cape Vidal, South Africa. The biogeographic break took the form of a transitional or overlap area corresponding in location to the Delagoa Bioregion, one of three bioregions also revealed by post-hoc analyses. Significant differences in total average biomass and trophic structure were evident among bioregions, with a number of inter-bioregional trends in trophic groups being apparent. In total, 12 reef community types were recognised, based on similarity profile permutation tests. Most reefs in the Subtropical Natal Bioregion were dominated by a community type characterised by a high biomass of the filter-feeding ascidian Pyura stolonifera and various species of articulated coralline algae. In the Delagoa Overlap Bioregion, a comparatively high diversity of community types was defined, many dominated by algal turf, P. stoloniferaand various Alcyonacea and Scleractinia. Further north, P. stolonifera diminished and the contributions of Scleractinia, especially Porites spp., Pocilloporaspp. and Galaxea spp. increased. Many of these community types are not represented within protected area networks, particularly those in southern Mozambique. When the biomass data were correlated with nine abiotic variables, likely determinants of community composition emerged at both inter- and intra-regional scales. Sea surface temperature, significant wave height, chlorophyll-a and suspended inorganic sediment were the variables highly correlated with community composition and therefore most likely to drive biogeographic differences. Within each bioregion, different sets of abiotic variables were found to be important in driving community differences among sites, including turbidity, chlorophyll-a, reef susceptibility to sand inundation, reef heterogeneity and sea surface temperature. Striking differences in the oceanographic conditions of bioregions were evident, especially between Subtropical Natal and Delagoa Overlap bioregions. In particular, the strong influence of wave height emerged as a novel and unexpected correlate at a biogeographic scale. These differences initiated a trophic study conducted in the Subtropical Natal Bioregion, aimed at determining the importance of riverine-derived POM subsidies in supporting the high filter-feeder biomass in this bioregion. Using carbon, nitrogen and sulphur isotopes and a three-source Bayesian mixing model to calculate proportional contributions, I determined that marine-derived POM formed the bulk of the diets of four species of filter-feeders, but the assimilation of riverine-derived POM was nevertheless notable, ranging from 8 to 33 %. I concluded that riverine POM is likely to play an important but secondary role to factors such as increased levels of turbidity and productivity in explaining the high filter-feeder biomass in the Subtropical Natal Bioregion. These findings provide the first evidence of riverine-inshore-pelagic coupling in filterfeeder communities in this bioregion, and throw light on the factors linked to large-scale biogeographic patterns. en_ZA
dc.language.iso eng en_ZA
dc.subject.other Zoology en_ZA
dc.title Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean en_ZA
dc.type Doctoral Thesis
uct.type.publication Research en_ZA
uct.type.resource Thesis en_ZA
dc.publisher.institution University of Cape Town
dc.publisher.faculty Faculty of Science en_ZA
dc.publisher.department Department of Biological Sciences en_ZA
dc.type.qualificationlevel Doctoral
dc.type.qualificationname PhD en_ZA
uct.type.filetype Text
uct.type.filetype Image
dc.identifier.apacitation Porter, S. N. (2009). <i>Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Biological Sciences. Retrieved from http://hdl.handle.net/11427/9018 en_ZA
dc.identifier.chicagocitation Porter, Sean N. <i>"Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2009. http://hdl.handle.net/11427/9018 en_ZA
dc.identifier.vancouvercitation Porter SN. Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Biological Sciences, 2009 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/9018 en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Porter, Sean N AB - The biogeography and ecology of benthic shallow subtidal reef communities in the western Indian Ocean is poorly known, particularly in north-eastern South Africa and southern Mozambique. This thesis uses quantitative information to resolve biogeographic patterns, define reef community types, elucidate potential abiotic determinants of community composition, and evaluate whether subsidies of riverine-derived particulate organic matter (POM) support filter-feeder biomass and drive biogeographic patterns. A large-scale biogeographic analysis was conducted using quantitative biomass data derived from 55 shallow subtidal reefs spanning five countries in the western Indian Ocean. Two statistically distinct marine provinces, Tropical Indo-West Pacific and Subtropical Natal, were recognised by differences in community composition and separated by a biogeographic break in the vicinity of Cape Vidal, South Africa. The biogeographic break took the form of a transitional or overlap area corresponding in location to the Delagoa Bioregion, one of three bioregions also revealed by post-hoc analyses. Significant differences in total average biomass and trophic structure were evident among bioregions, with a number of inter-bioregional trends in trophic groups being apparent. In total, 12 reef community types were recognised, based on similarity profile permutation tests. Most reefs in the Subtropical Natal Bioregion were dominated by a community type characterised by a high biomass of the filter-feeding ascidian Pyura stolonifera and various species of articulated coralline algae. In the Delagoa Overlap Bioregion, a comparatively high diversity of community types was defined, many dominated by algal turf, P. stoloniferaand various Alcyonacea and Scleractinia. Further north, P. stolonifera diminished and the contributions of Scleractinia, especially Porites spp., Pocilloporaspp. and Galaxea spp. increased. Many of these community types are not represented within protected area networks, particularly those in southern Mozambique. When the biomass data were correlated with nine abiotic variables, likely determinants of community composition emerged at both inter- and intra-regional scales. Sea surface temperature, significant wave height, chlorophyll-a and suspended inorganic sediment were the variables highly correlated with community composition and therefore most likely to drive biogeographic differences. Within each bioregion, different sets of abiotic variables were found to be important in driving community differences among sites, including turbidity, chlorophyll-a, reef susceptibility to sand inundation, reef heterogeneity and sea surface temperature. Striking differences in the oceanographic conditions of bioregions were evident, especially between Subtropical Natal and Delagoa Overlap bioregions. In particular, the strong influence of wave height emerged as a novel and unexpected correlate at a biogeographic scale. These differences initiated a trophic study conducted in the Subtropical Natal Bioregion, aimed at determining the importance of riverine-derived POM subsidies in supporting the high filter-feeder biomass in this bioregion. Using carbon, nitrogen and sulphur isotopes and a three-source Bayesian mixing model to calculate proportional contributions, I determined that marine-derived POM formed the bulk of the diets of four species of filter-feeders, but the assimilation of riverine-derived POM was nevertheless notable, ranging from 8 to 33 %. I concluded that riverine POM is likely to play an important but secondary role to factors such as increased levels of turbidity and productivity in explaining the high filter-feeder biomass in the Subtropical Natal Bioregion. These findings provide the first evidence of riverine-inshore-pelagic coupling in filterfeeder communities in this bioregion, and throw light on the factors linked to large-scale biogeographic patterns. DA - 2009 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2009 T1 - Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean TI - Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean UR - http://hdl.handle.net/11427/9018 ER - en_ZA


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