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  1. Home
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Browsing by Author "Sink, Kerry J"

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    Biogeography and potential factors regulating shallow subtidal reef communities in the western Indian Ocean
    (2009) Porter, Sean N; Branch, George M; Sink, Kerry J; Kaehler, Sven
    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.
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    Coral bleaching responses in Sodwana Bay, South Africa
    (2013) Harikishun, Ameil; Attwood, Colin; Sink, Kerry J
    This study assessed the bleaching response (BR) of coral colonies within the central reef complex in Sodwana Bay, South Africa. Bleach surveys were conducted at 16 sites on 8 reefs over the period of 2007 to 2013. A total of 12 858 coral colonies from 30 taxa were randomly sampled and colonies were placed into 7 categories of bleaching response. This allowed for the calculation of taxon-specific BR as a weighted percentage of coral cover bleached. Continuous temperature records from a permanent temperature gauge on Two Mile Reef were used to assess thermal stress over this period. The percentage of coral colonies that bleached in 2007, 2008, 2011, 2012 and 2013 were 37.4%, 17.4%, 23.8%, 33.6% and 38.8% respectively. A binomial GLM model framework was used to separate the effects of year, reef and taxon on the bleaching response. Due to inconsistent sampling of sites over time, only data from the seven sites on Two Mile Reef (TMR) and the two sites on Nine Mile Reef (NMR) were included in the model. A total of 6758 coral colonies from the nine most abundantly sampled taxa were used in the assessment of bleaching response for TMR and NMR over the sample period. Taxon was shown to explain most of the variability in the bleaching response of TMR and NMR over time (40.9%). The standardized reef bleaching response of TMR and NMR indicated the same temporal trends with a range of 5% to 28% of live coral surface bleached. Standardized reef-specific BR showed periods of high (2007, 2012 and 2013) and low (2008 and 2011) bleaching response. Low BR in 2008 and 2011 did not correspond to thermal stress (≥27.5°C) suggesting that local upwelling buffered the effects of thermal stress experienced. Standardized taxon-specific bleaching response for TMR and NMR displayed large variability over time and ranged from 2.5% to 45% of live coral surface bleached, with Montipora being the most susceptible and Galaxea and Playgyra being the least. Mean site-specific BR averaged over all years, including all sites, found that Coscinaraea, Montipora, Astreopora and Anomastrea were the most susceptible taxa. This study and other recent studies draw attention to a trend of either episodic or an increasing frequency and intensity of bleaching in southern African reefs.
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    Distribution and community structure of Chaetodontidae (Perciformes) in iSimangaliso Wetland Park with the view to applying the Butterflyfish Indicator Hypothesis in this region of South Africa
    (2014) Noble, Talitha Gaby; Attwood, Colin; Sink, Kerry J
    Coral reefs are globally in a vulnerable state, because of both human impacts and environmental alterations. An understanding of coral reef ecosystems and the ability to detect changes in the reef environment early on are necessary to apply effective conservation. The co-evolution of coral and coral feeding fishes means that some species may exhibit interactions useful for indicating reef health, acting as an early warning system. Chaetodontidae (Perciformes) are one such family, containing coral dependent (obligate corallivore) species. This concept is known as the Butterflyfish Indicator Hypothesis (BIH). Through the collection of baseline data for butterflyfish abundance, diversity and species composition, the possible applicability of the BIH was investigated within Marine Protected Areas (MPA¡¯s) of iSimangaliso Wetland Park, on the north-eastern coast of South Africa. Other factors possibly impacting butterflyfish distribution were also investigated in this region. These factors were level of MPA protection (sanctuary or partially protected), reef rugosity and site effects. 78 transects across 13 dive sites were swum using Underwater Video Census (UVC) for data capture. Reef rugosity displayed no impact on any of the sampled factors, whilst site and protection level did. Protection was the factor with the greatest influence on butterflyfish species richness (df = 77, t = 2.85, p < 0.005), evenness of spread (df = 77, t = 1.79, p < 0.05) and total abundance, as revealed by the General Linear Model (GLM) with the lowest Aikake¡¯s Information Criterion (AIC) (y = ¥âₒ + ¥â©û (protection)). None of the factors altered Chaetodon meyeri distribution significantly, the only observed obligate corallivore, for which low abundances were observed. Differences in total butterflyfish abundance and species diversity appear to be particularly useful in revealing human impacts on coral health. The lack of C. meyeri, likely accounted to low abundances of its preferred coral Acropora (Scleractinia: Acroporidae), suggest that the BIH is not useful in this region.
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    A hierarchical analysis of abiotic determinants and harvesting impacts in the rocky intertidal communities of KwaZulu-Natal
    (2001) Sink, Kerry J; Branch, George M; Harris, Jean M
    This thesis was undertaken to provide quantitative scientific information for decision-making and conservation planning for the previously scarcely studied rocky intertidal habitats in KwaZulu-Natal on the east coast of South Africa. Biogeographic patterns were resolved and abiotic determinants and harvesting impacts were identified at three different scales. A biotope classifiadion system was developed as a new tool for assessing the conservation status of intertidal communities, evaluating conservation priorities and monitoring change in intertidal habitats. The implications of the findings of this thesis for management and conservation planning were examined.
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    Quantitative fish survey of the submarine canyons of the iSimangaliso Wetland Park
    (2015) Geldenhuys, Dale Adam; Attwood, Colin; Sink, Kerry J
    There have been no quantitative studies of fish species associated with the submarine canyons of the north east coast of South Africa. These canyons offer protection to coelacanths Latimeria chalumnae, fish of commercial importance, and a number of protected and endemic species. A fish survey was conducted by remotely operated vehicle (ROV) that captured video footage at depths between 60 m and 160 m. Seven canyons (Island Rock, South Island Rock, Wright, Jesser, Diepgat, Leadsman and Chaka) and one deep reef (Diepgat Deep Reef) spread along 78 km of shelf break were surveyed. Fish were identified and counted in 1143 30-second video segments. Patterns in diversity and abundance were investigated with respect to canyon, depth, and habitat type. The survey found 52 fish species from 23 families. The families Serranidae and Sparidae were well represented. The first submarine images of the critically endangered Seventy†Four seabream are particularly noteworthy. Only three Myliobatidae species represented the Chondrichthyans. Variation in Shannon-Wiener species diversity (H') was influenced by the diversity of habitat (Kruskall†Wallis p<0,0001) and depths (Kruskall†Wallis p<0,0001). Mann†Whitney post hoc tests showed cave to have a higher H' than sandy plain (p<0,001) and wall (p<0,001). H' for margin was greater than sandy plain (p=0,001) and wall (p<0,001). H' for rock outcrop was greater than sandy plain (p=0,006). Fish diversity increased with increasing depth until 90m, thereafter diversity decreased with subsequent depths. Habitat (Permanova p=0,0031) had the strongest influence on fish community composition. No north†south separation in terms of fish diversity (H') among canyons was detected. The results were consistent with similar studies. All canyons were adequately sampled as the rate of discovery of additional species per sample was ≤1%. A minimum of 80 30-second samples per canyon is recommended to survey fish. The survey methods employed during this study are recommended for surveying deep reef fish to allow for meaningful comparative studies.
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    The biology, ecology and population trends of jacopever Helicolenus dactylopterus in South Africa
    (2021) Weston, Laura Frances; Attwood, Colin G; Sink, Kerry J
    Helicolenus dactylopterus is a deep-water benthic fish in the subfamily Sebastinae. Sebastinae species are slow-growing, long-lived and potentially vulnerable to overexploitation. Helicolenus dactylopterus is exploited throughout its Atlantic distribution. In South Africa, it is the eighth-most landed species in the demersal trawl fishery. Because little research has been conducted on H. dactylopterus locally, it is difficult to understand its response to fishing pressure. The life history, habitat preference and population trends of the species in South Africa were thus investigated. The age, growth, reproductive characteristics and diet were examined from 719 specimens collected from west and south coast trawls. The maximum age estimated was 32 years and the growth rate was low (k=0.13 year-1 ). Gamete release in both sexes was asynchronous, suggesting an unusual delay between insemination and fertilisation. Sperm storage was found in histologically analysed ovaries. The diet investigation indicated a selective benthic predator with an ontogenetic shift in diet from crustaceans to teleosts. To assess habitat preference, generalised linear models were fitted to broad and fine resolution abundance data from research trawls and video footage respectively. Trawl data indicated that H. dactylopterus primarily occurs in the Atlantic, decreasing in abundance in the Indian Ocean. Depths from 100 to 600 m were preferred, corresponding with the offshore demersal trawl footprint. Video data highlighted that H. dactylopterus, especially individuals >200 mm TL, preferred complex benthic habitat, typical of deep-water reef systems on the South African outer shelf and shelf edge. Standardised catch-per-unit-effort from trawl data indicated an increase in the abundance of H. dactylopterus from 1987 to 2001 in response to management reforms. Subsequently, a reduction in abundance occurred, but sustained population growth of 1.42% per year since 2005 suggests a national classification of the species as Least Concern against the IUCN Red List criteria. This study provides a thorough region-specific account of a previously data-limited species. Helicolenus dactylopterus shows life history traits typical of the Sebastinae, yet, in South Africa, the species has not succumbed to fishing pressure to the expected extent.
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