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    Decadal changes in land-use, water quality and fish assemblages in a KwaZulu-Natal urban and non-urban estuary.
    (2021) Van Schoor, Nikita.; Weerts, Steven.; Mackay, Christine Fiona.
    Globally, estuaries are recognised as highly dynamic environments which support diverse and productive flora and fauna, and provide numerous goods and services for human wellbeing. These systems are under threat from growing coastal populations that demand the transformation of natural land to accommodate urbanisation, agriculture, harbour, and infrastructure developments. Direct and indirect land-use/land-cover (LULC) changes adversely affect estuarine water quality, directly impacting estuarine biota such as fishes. While the short links between these components are known, few studies have attempted to integrate these links, particularly within the South African context. Therefore, this study aimed to integrate different levels of assessment (LULC and estuarine water quality) to describe changes in estuarine fish ecology over space and time. The study compared two permanently open estuaries in KwaZulu-Natal with distinct land-cover types, namely the uMgeni and uMlalazi estuaries. The uMgeni Estuary is surrounded by urban features and is situated in a highly developed catchment, whereas the uMlalazi is near-natural, with some surrounding agricultural areas. Historical land-cover imagery from the estuary to the 20 m topographical contour (inclusive of the Estuary Functional Zone), the estuary catchment land-cover, water quality and ichthyofauna data were collected. Land-cover types were grouped into eight categories and 42 feature classes based on modifications to the South African National Land Cover system, the United States Geological Survey and the Coastal Change Analysis Program. Multivariate statistical analysis identified two distinct groupings of land-cover types, Period 1 (before 1989) and Period 2 (during and after 1989). This period factor was then further used throughout the study to determine associated (temporal) responses in water quality and fish assemblages. Strong negative correlations were observed between dissolved oxygen and artificial land-cover types in the uMgeni Estuary. The results suggested that the uMgeni Estuary receives nutrient inputs from various urban activities, which reduce oxygen levels within the water column. Alterations to the hierarchical ichthyofauna structure in the uMgeni occurred on a year to year basis, relative to these anthropogenic impacts. In contrast, good water quality likely associated with fewer developments within the Estuarine Functional Zone has allowed the hierarchical fish structure in the uMlalazi Estuary to remain the same over time, although minor species level differences have occurred. The current state of each estuary was then investigated by measuring water quality parameters and sampling fish communities along the respective estuary gradients as determined by salinity penetration. Ichthyofauna and water quality data (salinity, turbidity, pH, dissolved oxygen) were collected within the lower, middle, upper and riverine reaches of each estuary. Each fish species sampled was assigned a functional guild depending on their use of the estuary and their feeding methods. The highly urbanised uMgeni Estuary was found to have an exceptionally degraded water quality in the upper reaches (average dissolved oxygen 3.78 mg l⁻¹). It supported a relatively low number of fish species (30) at a total catch per unit effort of 1488.7. In comparison, the less urbanised uMlalazi Estuary displayed much healthier water quality (average dissolved oxygen 6.94 mg l⁻¹), double the number of fish species (60) and higher total fish abundance (catch per unit effort of 2283.67). Salinity was primarily responsible for the longitudinal gradients in fish assemblage, reflecting the role of tidal influence in permanently open estuaries. Differences in fish communities between estuaries, however, were strongly influenced by oxygen levels within the water column. The uMgeni was primarily a detritus-based system that mostly supports small estuarine species (Ambassidae), detritivores (Mugilidae), and freshwater opportunists (Cichlidae). The uMlalazi Estuary is also a detritus based system, however, the diversity and fish assemblage suggests a more complex food web system across various feeding guilds, including piscivores, and is utilised extensively by marine and estuarine species. The results of this study highlighted the usefulness of incorporating guild and taxonomic distinctness tests in ecological studies. Additionally, they suggest that for the systems studied here, impacts of urban and land-use adjacent to estuaries are more detrimental to estuarine function than forestry or sugarcane cultivation. The results lend support to estuarine management and coastal development goals that aim to limit development in and around estuaries.
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    Physiological responses of a South African high-latitude coral community to global warming.
    (2021) Hanekom, Tanja.; Porter, Sean Nixon.; Sshleyer, Michael Henry.
    The health of the world’s coral reefs is deteriorating rapidly due to global climate change and increasing localised anthropogenic stressors. The substantial benefits resulting from coral reef ecosystems, economically and ecologically, requires that research be conducted on their responses to rising sea temperatures driven by climate change. Millions of people depend on the natural resources that coral reefs provide, whether for food or eco-tourism, trade and other indirect sources of income. Although South African coral reef communities lie within a long-established marine protected area, the iSimangaliso Wetland Park World Heritage Site, this status does not preclude them from being affected by the potential effects of global warming. Therefore, the objective of this study was to quantify several physiological parameters, including net community calcification (total alkalinity), growth (dimension and weight) and photosynthetic efficiency in the hard coral Acropora appressa, the soft coral Sinularia brassica and ‘live rock’ under local historical-average (24.4°C), future (26.9°C) and bleaching-threshold (28.8°C) temperatures indicative of climate change conditions projected at Sodwana Bay. Corals and live rock were exposed to the three different temperature treatments during a 10-week long mesocosm experiment that consisted of three phases: the initial phase during which temperatures were increased from 24.4°C over four weeks to reach setpoints of 26.9°C (future) and 28.8°C (bleaching threshold), respectively; the middle phase during which temperatures were held stable at each treatment’s setpoint for the proceeding four weeks; and the final phase during which a further 1°C increase was done over two weeks in the bleaching-threshold treatment to simulate an extreme warming scenario. An initial increase in size was evident in both coral species exposed to the historical-average control temperature and the future temperature projected for Sodwana Bay in 2100 by the representative concentration pathway (RCP) 4.5 climate change scenario. Although the growth trends of both species persisted in the control treatment, the overall linear growth of A. appressa was lower under the RCP 4.5 climate change temperature scenario and bleaching-threshold temperature relative to the control temperature. While no significant treatment effects were found, a decrease in the linear extension of A. appressa was evident at the end of the experiment at the bleaching-threshold temperature relative to the control temperature. Continuous growth trends were evident in the control and RCP 4.5 climate change scenario for S. brassica, however a reduction in diameter after 5 weeks was apparent in the bleaching-threshold treatment. A gradual increase in buoyant weight of A. appressa was evident across all treatments and experimental phases, with a slower growth rate only apparent towards the end of the experiment in the bleaching-threshold treatment. The buoyant weight of S. brassica decreased up until the start of the middle phase in the control treatment and RCP 4.5 treatment. However, an increasing trend in the weight of S. brassica was measured in the same two treatments from the end of the middle phase until the experiment concluded. Contrastingly, the weight of S. brassica in the bleaching-threshold treatment continued to decrease throughout the course of the experiment. Pulse-amplitude modulated fluorometry measurements of the photosynthetic efficiency of both A. appressa and S. brassica were lower under the temperature conditions projected by the RCP 4.5 scenario and by the bleaching-threshold temperature, relative to the historical-average control temperature. Contrastingly, live rock showed no significant differences in photosynthetic efficiency among the different temperature treatments. On average, total alkalinity levels were higher under future temperature conditions projected by the RCP 4.5 temperature scenario and by the bleaching-threshold temperature, relative to the control temperature, indicating suppressed net community calcification. Suppressed net community calcification was particularly evident during (week 6) and at the end (week 8) of the middle phase of the experiment. The experiment revealed that exposure to temperatures equivalent to those projected by the RCP 4.5 climate change scenario in 2100 and the local bleaching threshold are likely to be deleterious to high-latitude corals and coral reef communities in South Africa: buoyant weight and dimension, as well as photosynthetic efficiency were negatively affected in both species of coral and net community calcification was supressed under the two future climate scenarios of warming. Due to the location of Sodwana Bay reefs, the results indicate that calcification processes will be an essential physiological response to consider under global warming conditions. However, as high-latitude reef areas generally fared better during recent bleaching conditions, these reefs can be utilised to improve climate-change projection models. Such model improvements can guide climate policymakers in enhanced conservation efforts that will further stakeholder engagement and outreach. Accordingly, urgent action is needed to reduce greenhouse gas emissions to minimise the effects of global warming on coral reef communities as much as possible. Such efforts will further help to attain the 2°C Paris Climate Agreement and improve socioeconomic development for the management of reefs.
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    Zooplankton dynamics during a regime shift in the St Lucia Estuary, South Africa.
    (2021) Govender, Merusha.; Carrasco, Nicola Kim.
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    Macrofauna diversity of unique, fluvially-dependent soft-sediment habitats in the Uthukela Marine Protected Area, South Africa.
    (2021) Badenhorst, Stacey.; Mackay, Christine Fiona.
    The uThukela shelf is a large section of the KwaZulu-Natal (KZN) Bight, and being situated adjacent to the largest river on South Africa’s east coast and the fluvially-dominated uThukela Estuary, is an excellent example of a fluvially-dependent coastal ecosystem. Previous studies found that this shelf contains structurally and functionally unique macroinvertebrate communities that contributed to the promulgation of the uThukela Marine Protected Area (MPA), as part of the South African MPA network of 20 new or extended systems. This study expands on this evidence using recent samples collected prior to the protection of the uThukela shelf to provide a good baseline database for future monitoring within the MPA. The uThukela macrofauna distributions and the environmental parameters correlated with these patterns were investigated through replicated sediment grabs that were collected with corresponding abiotic parameters, along coast-perpendicular transects. Macrofauna were subsequently classified taxonomically and their functional attributes determined. One replicate collected on the innershelf was particularly noteworthy as the taxa composition was unique and unexpected for a mud depocenter as it was indicative of hard substrata, suggesting a nearby low-lying reef. This habitat anomaly should be further investigated as it may play an important role in biodiversity and ecosystem functioning within the uThukela benthic system that mostly consists of soft sediments. Overall, the uThukela shelf soft-sediment community represented a wide variety of taxa but in low abundance, and was dominated by burrowing polychaetes. These ubiquitous polychaetes exhibited diverse biological traits, and a finding of this study was that this group alone is a potential surrogate for future studies and monitoring of the entire uThukela shelf macroinvertebrate community. This community consisted of mostly facultative deposit feeders that shift to suspension-feeding and rely significantly on terrestrial particulate organic matter (POM) and mud deposited onto the shelf by the fluvially-dominated uThukela Estuary. The adaptive behaviour of these taxa allows intermittent shifts in food acquisition when conditions do not favour this optimal deposition (such as during reduced fluvial outflow), thereby enhancing ecosystem resilience to natural environmental fluxes. Natural fluctuations in the uThukela River flow results in reduced freshwater penetration onto the shelf during the dry (winter) season, and was observed during this study by the higher-than-expected salinity measurements further inshore and the resultant atypical salinity gradient across the uThukela shelf. Salinity, along with dissolved oxygen, were the measured near-bottom water parameters most correlated with macrobenthic distribution. Sediment composition also affected distribution patterns, forming fine-grained and medium-coarse-grained assemblages on the inner and mid-shelf, and a muddy assemblage on the outer-shelf. The muddy outer-shelf is mostly old deposits that suggests the uThukela has functioned as a fluvially-dominated system for a long time. Overall, sediments contained a large amount of crushed-shell and high Foraminifera abundances, contributing to habitat complexity and increasing diversity. Maintaining macrofauna diversity by preserving benthic habitats is vital in the functional success of marine ecosystems; particularly so in the uThukela system that is classified as strongly benthic-driven. This study provides baseline information contributing to future monitoring of whether the uThukela MPA achieves the aim of protecting rare benthic habitats associated with the connection of the coast to the deep sea and whether macrofauna diversity and associated ecological processes are maintained. In addition, it will support future studies within the MPA that emphasise the importance of the critical role of freshwater to the marine system and that ensure areas important for life-history strategies of vertebrates and invertebrates with high conservation status are conserved.
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    Macrobenthos used to validate multi-criteria derived marine biodiversity spatial zones in KwaZulu-Natal, South Africa.
    (2017) Maduna, Sikhumbuzo Mthunzi.; Mackay, Christine Fiona.
    Compared to terrestrial ecosystems, the characteristics of marine ecosystems remain largely under-explored. Marine and coastal ecosystems provide a number of ecological services and societal benefits (resources for commercial opportunity, food, recreation, and transport) which, in turn, has developed a strong reliance on these ecosystems. However, the increasing direct extraction of living and non-living resources and effects of urbanisation of adjacent coasts has placed a significant loss of habitats and associated essential diversity. To conserve biodiversity and retain specific goods and services provided by these ecosystems, marine conservation plans aim to protect spatial areas that are critical in the support of these benefits. Due to the paucity of adequate biological data and the prohibitive cost of directly sampling benthic biota over large areas, the most effective means of developing benthic habitat maps, used as biodiversity surrogates, is to use commonly available marine abiotic attributes. In KwaZulu-Natal (KZN), through marine spatial planning (MSP) the derivation of a marine conservation plan is well underway. The next step is to expedite the plan by investigating whether surrogates for biodiversity exist at different ecosystem levels, one being the infauna of unconsolidated sediments, mid-shelf 50-80 m. This work presents an outcome of the ACEP ‘Surrogacy Project’ that assessed whether predefined biodiversity zones (biozones) represent the taxonomic/functional attributes of macrobenthic communities. Biozones were subdivided into various subclusters from Richards Bay to uMkhomazi with 19 (57 replicates) stations sampled during the winter of 2014 across the biozones to represent replicate ‘treatments’. Macrobenthic communities were classified taxonomically, to the lowest level possible, and then on biological traits. Community patterns were investigated along the mid-shelf, and related to measurable biophysical factors. Environmental parameters measured included sedimentary characteristics as well as the bottom 5 m of water column characteristics per station. A total 33 215 individuals belonging to 634 taxa were recorded along the mid-shelf, of which the majority were Polychaeta and Crustacea, with the latter being highly abundant. Cluster analysis resolved into seven taxonomic groups distributed according to different habitats that are characteristic to the KZN shelf. The use of coarser taxonomic resolution (Phylum-Genus) or indicator taxa (Polychaeta and Amphipoda) as surrogates for total community richness were independently investigated using the same macrofaunal abundance data. Results showed similar clustering of samples to total fauna (Species-level) when data were analysed at Family-Genus taxonomic level and at Polychaeta indicator taxa, suggesting that the same amount of information was being gained using data based on these taxonomic level and indicator taxa. The results of the BIOENV analyses were also broadly similar for both taxonomic levels of analyses, in terms of both the proportion of the variation in assemblage structure explained by the selected environmental variables and the choice of selected variables. These results suggested that the information gathered at Family-Genus level and Polychaeta indicator can be used as a proxy for the whole macrobenthic community. This has important implications for future studies and for MSP. Using nine traits, across 51 categories, four main functional groups were found off Thukela, Zinkwazi to Durban, and Durban to uMkhomazi. The groups were characterised as being free-living carnivores, hard-skeleton direct-developing omnivores, and soft-bodied or hard-shelled omnivores with planktotrophic larvae. These patterns were explained by the KZN shelf habitat complexity, including level of different sediment grains, TOC, carbonates, water column turbidity, salinity, dissolved oxygen and temperature. Thus far, distribution patterns and functional attributes of the macrobenthos do not fully agree with modelled biozone separations (KZN MSP biozone model). Because they are an important component of marine ecosystem functioning, biozone model derivations require the addition of a macrobenthic component, in particular information about diversity patterns, to identify areas for conservation. Suggested, is a refinement of the current benthic habitat layer by incorporating biological data. Further, by using validated sediment distribution, taxonomic and functional attributes that determine soft-bottom macrofaunal distribution at a variety of spatial scales, an alternative biozone model to the current MSP predefined biozones was proposed. This multi-approach resolved into a simplified model with four biozones. These are likely better predictors of spatial variation in ecosystem processes and biodiversity as domains that are biologically informed, and are a key requirement for effective marine management. This study demonstrates the critical importance of testing assumptions about surrogacy and an approach for refining surrogates. Further studies are required to establish whether the proposed model adequately represents other ecological components (e.g. epifauna). The findings of this study contribute significantly to existing local knowledge, including augmenting and refining taxonomic information of the KZN shelf. In addition, this study subsidises poor information for large spatial areas in local and national marine conservation plans. The proposed biozone model may facilitate an understating of ecosystem process in the region and contributes to integrated marine management.
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    Community dynamics of meiofauna during a wet phase in the St Lucia estuarine system, South Africa.
    (2015) Naidoo, Bryaleen Leesa.; Perissinotto, Renzo.; Bownes, Sarah Jane.
    Meiofauna are an important component within the benthic environment of any aquatic habitat. Despite their significance and ubiquitous nature, these organisms are relatively poorly studied in Africa. Following a decade long drought period, the St Lucia Estuary experienced higher than average amounts of rainfall at the end of 2010. These heavy rainfall events replenished the freshwater capacity of the system, raising the water level and subsequently reducing salinity throughout the estuarine lake, thus marking the start of a two year long wet phase. Meiofauna community dynamics were assessed to determine their response to a wet phase and to the disturbance brought on by intense rainfall. Diversity indices and a host of multivariate analyses were used to gain an understanding of the meiofaunal communities of the system during this wet phase. Meiofaunal density and richness tended to be higher during the first year of the wet phase. Meiofauna communities within each site became more homogenous in the second year of the wet phase, indicating a more established community adjusted to wet conditions. Following a flood disturbance in early January 2011, meiofaunal communities at each site differed in terms of primary and secondary colonisers. Over time, communities increased in dissimilarity, suggesting succession at some level. A successional pattern was observed as the taxonomic composition of the communities shifted over time. The lack of a climax community in St Lucia in the medium term was likely due to the uneven impact that the lake experienced with the onset of the disturbance, with the northern reaches experiencing a greater degree of impact than the southern reaches. The continuity in disturbance occurrences also caused the system to move back to a previous successional state. The meiofauna of St Lucia are therefore able to recover after disturbances related to a wet phase and maintain some form of resilience. In the long term, meiofaunal communities may require a longer time period, than the one considered in this study, to reach the levels of abundance previously recorded.
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    Ecophysiology of intertidal corals along the east coast of South Africa : coping in marginal habitats.
    (2014) Smit, Kaylee Pam.; Glassom, David.
    Coral survival in a time of climate change will depend largely on the ability to tolerate, acclimatise and adapt to changes in their natural environment. High-latitude intertidal corals along the east coast of South Africa withstand extreme temperature fluctuations, and endure highly marginal conditions for coral survival and growth. Intertidal corals have largely been ignored throughout years of coral research, yet they provide scope for understanding adaptation and acclimatisation in marginal conditions. With focus on two scleractinian species occurring in rock pools, Pocillopora verrucosa and Anomastrea irregularis, the aim was to compare population size distributions and physiological responses (zooxanthellae density, chlorophyll a and lipid content) to season and latitude. Heterotrophy as a coping mechanism was also investigated. Five sites along the KwaZulu-Natal (KZN) coastline were sampled to determine latitudinal differences, from Sodwana Bay (27°S) to Munster (31°S), the southernmost point of coral distribution in this study. Rock pools experience large temperature fluctuations over short time periods, emphasising the acute thermal stress endured by corals. At spring tide temperatures can fluctuate by more than 10°C over one tidal cycle. Temperatures in rock pools along the coast are a function of rock pool size and depth rather than latitude, with short-term fluctuations not seeming harmful to corals. Coral population structure provides insight into the life history, juvenile input and mortality of these intertidal corals. High variability in size distributions between sites suggests that different disturbances are acting on intertidal coral populations and localised conditions are likely structuring these communities, nevertheless, populations see relatively stable and likely to persist in these habitats. Zooxanthellae density and lipid content decreased from summer to spring in P. verrucosa, whereas A. irregularis showed minimal seasonal patterns. Chlorophyll a was highest in winter in both species, possibly in response to low temperatures and light. Differences in δ¹³C and δ¹⁵N between coral tissue and zooxanthellae suggest that heterotrophy contributes more to the metabolism of A. irregularis than P. verrucosa. Isotope signatures also reveal that corals at Sodwana Bay are either feeding less or comprise a different diet to those at other sites. Lipid utilisation and heterotrophy may comprise important energy sources in coping with marginal conditions of the intertidal zone. Rock pools may thus constitute and important habitat for coral survival, growth and reproduction, allowing the southward extension of their range, which will be imperative during times of local and global environmental change.
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    An investigation of the population connectivity of sardines (Sardinops sagax) of the KZN sardine run using meristic, morphological and genetic data.
    (2014) Chiazzari, Brent.; Macdonald, Angus Hector Harold.; O'Donoghue, Sean Henry.
    The Sardine run occurs annually when large schools of sardine (Sardinops sagax) move from the Agulhas Bank towards KwaZulu-Natal, and has significant ecological and anthropogenic importance. Recent investigation has highlighted the nature and mechanisms resulting in the sardine run, however, critical questions about why the sardine run occurs remain unanswered. Therefore, the aim of this project was to elucidate the population diversity, connectivity and structure of sardines undertaking the sardine run. Sardines were sampled at four sites along the South African coast, and their morphology assessed using meristic data, multivariate, and geometric morphometrics. Nine exon-primed, intron-crossing (EPIC) DNA markers and the mitochondrially encoded cytochrome oxidase I (mtCOI) region of DNA were used for population and phylogeographic genetic analyses. Morphological analyses revealed significant differences between head size and shape of sardine run stock compared with other regions, and supports the delineation of a western, southern and eastern South African stock. Phylogeographic analysis using cytochrome oxidase I data, supported the idea that the Sardinops genus is monotypic. Genetic analyses using EPIC data confirmed low levels of segregation between sardines from the sardine run and the Western Cape stock. However, larvae spawned in KwaZulu-Natal demonstrated moderate levels of isolation from the Western Cape stock. The results reveal that there is successful recruitment of KwaZulu-Natal juveniles to the adult stock undertaking the sardine run. KwaZulu-Natal juveniles also recruit to the Western Cape population, although, to a lower degree. Results suggest sardines from the West Coast and Agulhas Bank partake in the sardine run. However genetic evidence suggests a certain subpopulation of the Agulhas Bank and a sub-stock of the Western Cape stock spawn successfully in KwaZulu-Natal. These results support the hypothesis that the sardine run represents a subpopulation spawning migration of Sardinops sagax in South Africa.
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    Diversity and distribution of subtidal soft-bottom macrofauna of the Isimangaliso Wetland Park, South Africa.
    (2014) Harmer, Rogan Will.; Glassom, David.
    There have been no previous studies describing the subtidal soft-bottom macrofaunal assemblages of the iSimangaliso Wetland Park or how they are influenced by the ecological and environmental processes associated with coral reef proximity. With South Africa having high wave energy the transportation of nutrients and organisms between the soft-bottom areas and reef habitats is probable. This transfer of resources may create ecological linkages which organisms depend on. The aim of this study was to document the species diversity, distribution and abundance of in- and epi-macrofauna in iSimangaliso Wetland Park and to relate these to depth, sediment grain size, location, reef proximity and protective status. Macrofauna were collected using an air-lift design suction sampler. The macrofauna were identified to the lowest possible taxonomic level, biomass estimates were calculated and sediment grain size was determined. A total of 5166 animals were collected and 121 macrofauna species were identified. Macrofaunal assemblages inhabiting the soft-bottom sedimentary habitat surrounding the reefs changed in species abundance and diversity with increasing distance from the reef. Lower abundances and diversity were found closest to the reefs strongly indicating that the macrofaunal assemblages were negatively affected by the reef proximity. Although reef proximity was indicated as influential, environmental gradients were found to be more important in defining community structure. Higher percentages of coarse sediments found closest to the reef edge coincided with lower abundances, biomass and species richness of macrofauna. Trends of higher abundances at the middle distance indicated hydrodynamic disturbance may be affecting near shore assemblages. Sediment grain size and hydrodynamic disturbance both appeared to be the main determinants of assemblage structure around reefs. Trophic interactions by reef associated predators were indicated by lower macrofaunal abundances recorded at close proximity to the reefs.There was no evidence for the presence of a latitudinal diversity gradient as localised environmental conditions were found to be more influential in determining soft-bottom macrofaunal community structure and distribution in the iSimangaliso Wetland Park. The presence of ecological linkages between soft-bottom macrofaunal communities and coral reefs gives insight into the important roles soft-bottom macrofauna play in the functioning of the iSimangaliso Wetland Park marine reserve. The documentation of the species diversity and distribution of macrofauna in the soft-bottom habitats will provide valuable baseline information for the future management strategies.
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    Impact of turbidity on pseudodiaptomus stuhlmanni, a dominant copepod in Lake St Lucia, iSimangaliso Wetland Park.
    (2015) Jones, Salome.; Perissinotto, Renzo.; Carrasco, Nicola Kim.; Vosloo, Andre.
    Although the St Lucia Estuary is a Ramsar Wetland of International Importance, it has historically been subjected to human-accelerated ecological stressors. One of these is high turbidity resulting from excessive sediment inputs. Laboratory-based studies have revealed a negative turbidity effect on the feeding and mortality rate of two dominant zooplankton species, the mysid Mesopodopsis africana and the calanoid copepod Acartiella natalensis. The first aim of this study was to determine the effect of turbidity on the feeding, respiration, and mortality rate of another important calanoid, Pseudodiaptomus stuhlmanni. Although this species was negatively affected by high turbidity, it was substantially more tolerant than M. africana and A. natalensis. The second aim was to test the field response of the dominant St Lucia zooplankton to a silt plume-causing flood event that occurred in March 2014. As M. africana was not abundant in the system prior to this event, attention was paid to the copepods. The field response of A. natalensis and P. stuhlmanni were in good agreement with the findings from the laboratory-based experiments. The population of A. natalensis underwent an immediate, and sharp decline, whereas that of P. stuhlmanni only declined in April 2014, after a month of surviving in highly turbid waters. However, P. stuhlmanni also took longer to recover, but this may be attributed to the attachment of parasitic epibiotic ciliates to this species. Therefore, although to different degrees, turbidity negatively impacted the dominant St Lucia zooplankton species. Through its observed positive correlation with the parasitic ciliates, turbidity further suppressed the abundance of the most turbid-water tolerant species, P. stuhlmanni. The importance of carefully managing sediment loading in St Lucia is stressed, as the effect of turbidity on zooplankton likely has food web-wide consequences.
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    Molecular revision of Zoantharia (Anthozoa Hexacorallia) on the east coast of South Africa.
    (2014) Risi, Michelle Megan.; Macdonald, Angus Hector Harold.
    The order Zoantharia (Cnidaria: Anthozoa) is ubiquitous on the east coast of South Africa, and despite their widespread distribution they are poorly represented in literature. No molecular identification has been carried out on these organisms on the South African shoreline. Zoanthus sansibaricus Carlgren, 1900 has a global distribution and has been reported having numerous morphotypes in terms of polyp shape, size, colour and oral disk colour. The initial aim in this study was to examine the molecular characteristics of three Zoanthus species; Z. sansibaricus, Z. durbanensis Carlgren, 1938 and Z. natalensis Carlgren, 1938, to determine whether they are three separate species or merely morphotypes of one another. Following on from this research, the aim was to conduct a molecular revision of all zoanthids found in the intertidal zone along the east coast of South Africa, and to identify the Symbiodinium spp. within zoanthids for comparisons with conspecifics elsewhere. Samples were collected at sites along the coast from Umgazana (31.7024° S, 29.4175° E) to Sodwana (27.6594° S, 32.6477° E) and at one site in Libanona, Madagascar (25.0421° S, 46.9952° E). Sequences of cytochrome oxidase subunit one (COI), mitochondrial 16S ribosomal DNA (mt 16S rDNA), the nuclear internal transcribed spacer region of ribosomal DNA (ITS rDNA) for zoanthids and ITS-rDNA region for Symbiodinium spp. were used in this study to run phylogenetic analyses and examine the molecular characteristics for comparisons with zoanthids elsewhere using GenBank. Seven species were identified; Isaurus tuberculatus, Palythoa nelliae, Palythoa tuberculosa, Z. durbanensis, Z. gigantus, Z. natalensis and Z. sansibaricus. The COI sequences (for Z. sansibaricus, Z. natalensis and Z. durbanensis) had little variation between species groups, while the mt 16S rDNA tree showed that Z. sansibaricus matched with sequences of previously reported Z. sansibaricus from the Pacific. Zoanthus natalensis was identical to Z. kuroshio Reimer & Ono, 2006 and Z. durbanensis was identical to Z. vietnamensis Pax & Müller, 1957. The ITS rDNA sequences were very similar for these four species; Z. natalensis, Z. kuroshio, Z. durbanensis and Z. vietnamensis. Palythoa nelliae Pax, 1935 appears to match with Pacific species Palythoa mutuki Haddon & Shackleton, 1891, and this is supported by the mt 16S and ITS rDNA markers. Symbiodinium subclade A1 was most often found with Z. natalensis and subclade C15/C91 was most often found with Z. durbanensis. Subclade C1 sensu LaJeunesse (2002) was found with all Isaurus and Palythoa samples, and most of Z. sansibaricus samples. The results of this study indicate that Z. natalensis is likely conspecific to Z. kuroshio, Z. durbanensis is likely conspecific to Z. vietnamensis, and P. nelliae is likely conspecific to P. mutuki, however, this is only a tentative hypothesis as no formal morphological analyses were done on proposed conspecifics.This work highlights the importance for similar studies in the clarification of zoanthid taxonomy
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    Post-Harvest seed physiology and conservation of the germplasm of syzgium cordatum hochst.
    (2013) Cheruiyot, Anastacia Chepkorir.; Kioko, Joseph Ivala.
    There is global concern about the ex situ conservation of the germplasm/genetic resources of recalcitrant-seeded species. While orthodox (desiccation tolerant) seeds afford an ideal means for ex situ conservation, this is impossible for recalcitrant seeds which are shed at high water contents, are metabolically active, and are desiccation sensitive, with those of many species losing viablity when only a small proportion of tissue water has been removed. Storing such seeds in the short- to medium-term is possible when parameters to be optimised include the means to obviate dehydration and the most equitable storage temperature – and, if necessary – the best way to curb the activity of seed-associated micro-organisms (usually fungi) during such hydrated storage. Presently, it is generally agreed that the only option for longterm ex situ conservation of the germplasm of recalcitrant-seeded species is by cryopreservation (usually in liquid nitrogen) of explants representing the same genetic diversity as do the seeds. To achieve this, the explants of choice are embryonic axes excised from the seeds. However, there are still many problems impeding progress particularly for tropical/sub-tropical species: presently, these need to be resolved on a species-specific basis. To this end, the current investigation was focused on germplasm of the tropical/sub-tropical recalcitrant-seeded species, Syzygium cordatum Hoechst. There were two major aspects to the study, viz. optimisation of the ‘shelf-life’ of intact seeds in the interest of almost immediate planting programmes, and attempting to develop a protocol which would result in successful cryopreservation of zygotic axes excised from the seeds. Chapter One of this Thesis provides an overview of the theoretical basis underlying these two approaches to conservation, as well as a description and significance of the species under study. Chapter Two describes the study seeking to establish optimal short-term storage conditions for the recalcitrant seeds of S. cordatum. Seeds were stored at various relative humidities at three different temperatures (6 ºC, 16 ºC and 25 ºC) for differing periods. Seeds stored at all these temperatures maintained stable water contents. The most mature seeds that were stored in a saturated atmosphere at both 16 ºC and 25 ºC reached their root protrusion stage after three weeks. This, however, occurred in only a small percentage of the seed batches. The majority of the seeds that were stored under saturated atmospheric conditions at 16 ºC and 25 ºC had not reached the stage of radicle elongation before the sixth week of storage, but after this time there was evidence of damage associated with both fungal proliferation and desiccation sensitivity. Seeds stored at 6 ºC and 25 ºC for the longest period had also lost vigour. For seeds stored at 6 ºC and 25 ºC (whether under hydrated or nonhydrated conditions), those stored for the shortest and longest periods produced the smallest seedlings. The seeds stored at 16 ºC appeared to have maintained vigour and seedling size did not change with the period of seed storage prior to sowing. Storage at 6 ºC may have caused stress associated with chilling, while at 25 ºC, seed storage was compromised by fungal proliferation. Those seeds stored in unsaturated atmospheric conditions at 16 ºC exhibited an increase in their germinative index and germination rate after six weeks. This is possibly associated with the ability of seeds, where vigour was not compromised, to counteract fungal proliferation because there was a decrease in the number of seeds showing fungal proliferation. In contaminated seeds, the fungus appeared to proliferate from the surface of the coat, to the cotyledons and eventually to the axes. Seeds generally did harbour fungal inoculum at harvest, but proliferation, was reduced at cool temperatures.Based on the above observations, storage in sealed plastic bag (non-saturated atmospheric conditions) at 16 ºC was chosen for the short-term maintenance of seeds of S. cordatum. The studies described in Chapter Three sought to establish a protocol for the cryopreservation of embryonic axes of S. cordatum. These studies involved the stepwise optimisation of decontamination, regeneration and growth, dehydration, cryoprotection and cooling (freezing) conditions. The most suitable combination of biotechnological manipulations for the preparation of embryonic axes of S. cordatum for cryopreservation were: decontamination by exposure to 1% (v/v) Ca(OCl)2 for 5 min; cryoprotection using a 5% solution of dextran and DMSO for 1 h followed by exposure to a 10% solution of these cryoprotectants for another hour; then dehydration in a flash dryer for 75 min; and regeneration in agitated liquid medium containing woody plant medium, 10 g l-1 polyvinylpyrrolidone and 75 mg l-1 citric acid. A major achievement following this procedure, was the prevention of excessive exudation of phenolic compounds from the explants. Nevertheless, despite optimisation of all these procedures, axes did not survive cryogenic exposure. One of the objectives of the present study was to develop the means for visualisation of intracellular detail of axis cells of S. cordatum. An experiment was thus entrained to investigate the effects of exposing shoot tips to 75 mg l-1 citric acid for 10 min before fixation during preparation for transmission electron microscopy. In the absence of any ameliorative treatments, large electron dense polyphenolic precipitates were observed mainly inside vacuoles closely associated with the tonoplast. Less dense, small precipitates were located between the plasmalemma and the cell wall, and organelles were generally not clearly visible, probably because of leaching of phenolics into the cytoplasm. Thus the effects of various treatments on organelles and the entire cell ultrastructure could not be conclusively determined. When treated with citric acid, cells had no visible polyphenolic precipitates and the apparently intact organelles were clearly visible, so paving the way for electron microscopical examination of this – and perhaps any other – plant tissue containing substantial amounts of phenolic substances.
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    Chemical cue interactions between alien invasive and native aquatic gastropods in the iSimangaliso Wetland Park, South Africa.
    (2013) Raw, Jacqueline Leoni.; Perissinotto, Renzo.; Miranda, Nelson Augusto Feranandes.
    The importance of chemical cues in mediating interactions among individuals and structuring communities is being increasingly recognized in aquatic environments. Chemical cues have been shown to drive predator-prey interactions in which behavioural responses in terms of movement have been reported. The role of chemical cues in mediating interactions between heterospecific competitors, in which there is an observed behavioural response, has not been previously investigated. This research project has used the biological invasion of Tarebia granifera, a caenogastropod endemic to south-east Asia, to determine the role of chemical cues in driving displacement interactions with native gastropods within coastal lakes and estuarine environments of the iSimangaliso Wetland Park, in northern KwaZulu-Natal, South Africa. An experimental approach was used to measure behavioural responses of gastropods to chemical cue treatments by quantifying components of movement. Responses of three dominant native gastropods within Lake St Lucia were tested in a preliminary in situ experiment. The mean Displacement, mean Number of Steps and grand mean Turning Angle were determined from recorded pathways of individual gastropods using image-processing software. Responses to chemical cues released by T. granifera were significantly different and negative in comparison to the control and conspecific chemical cue treatments. Following these results, the experiment was repeated and refined to include responses between native heterospecific gastropods from populations within the larger geographical range of the iSimangaliso Wetland Park. Additionally, the case of whether the observed responses could be attributed to build up of metabolic waste products was also investigated. The results confirmed those of the preliminary in situ study. Negative responses were only reported for gastropods which did not have a shared evolutionary history with T. granifera, irrespective of metabolic waste concentrations Native gastropods moved away from chemical cues released by T. granifera using a directed orientation mechanism. Interestingly, native gastropods did not exhibit this behavioural response to chemical cues of other heterospecifics. This suggests that T. granifera has developed chemical cues under evolutionary pressure, which act as deterrent on naïve gastropods. The implications for these responses are considered within the framework of Movement Ecology with contributions to Chemical Ecology. The potential of this interaction as a mechanism of invasion to be included within spread models is discussed.
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    Phosphorus distribution among selected abiotic and biotic components of two KwaZulu-Natal estuaries, South Africa.
    (2013) Vezi, Madonna Sduduzo.; Scharler, Ursula Michaela.
    Phosphorus is an essential element since it controls primary productivity in aquatic ecosystems and its excess can lead to eutrophication in receiving systems. The aim of this project was to determine phosphorus distribution in biotic and abiotic nutrient pools of two KwaZulu-Natal estuaries. Samples of dissolved inorganic phosphorus (DIP), particulate phosphorus (PP), phytoplankton, microphytobenthos, zooplankton, macrozoobenthos and sediment were collected in the temporarily open/closed Mpenjati (MP) and permanently open Mlalazi Estuary (ML) during May (ML), September (MP) and November (ML+MP) using standard methods. Chlorophyll a concentrations as well as species richness, abundance and biomass of zooplankton and macrozoobenthos were analysed. Living and non living nutrient pools were analysed for phosphorus and were compared between stations, sampling sessions, estuaries and taxa. Zooplankton abundance and biomass in the Mlalazi Estuary was higher during May than November. In the Mpenjati Estuary highest zooplankton abundance and biomass was recorded during September than November. No significant differences were apparent in abundance (p = 0.217) and biomass (p = 0.974) of zooplankton between the two estuaries. Macrozoobenthos abundance and biomass in the Mlalazi Estuary was higher during May than November. In the Mpenjati Estuary macrozoobenthos abundance and biomass was higher during November than September. Significant differences in abundance (p = 0.003) and biomass (p = 0.020) were apparent between the estuaries. Sediment to a depth of 10 cm comprised the highest phosphorus biomass than any other nutrient pool in both Mlalazi (4871.1 mgP·m⁻² ± 5888.9 SD) and Mpenjati (2578.6 mgP·m⁻² ± 1828.0 SD) estuaries followed by DIP (120.5 mgP·m⁻² ± 177.7 SD and 5.9 mgP·m⁻² ± 6.1 SD respectively). In both estuaries, the lowest phosphorus biomass was contained in zooplankton with both estuaries containing zooplankton P biomass of 0.001 mgP·m⁻² ± 0.002 SD. Particulate phosphorus and DIP concentrations were higher in the upper reaches in both estuaries indicating that rivers were the main sources of this nutrient in these systems. The Mlalazi Estuary had higher nutrient levels than the Mpenjati Estuary. Such elevated nutrients can be enhanced by the continuous river flow into the permanently open estuary. In both estuaries, no significant differences were apparent in zooplankton and macrozoobenthos P content between different taxa.
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    Dietary dynamics of two key fish species in the St Lucia estuarine system, South Africa.
    (2014) Dyer, David Clifford.; Perissinotto, Renzo.; Carrasco, Nicola Kim.
    Among the 155 species of fish recorded so far in the St Lucia estuarine lake, Oreochromis mossambicus and Ambassis ambassis are the two most prominent. Although originally endemic to southern Africa, O. mossambicus is now one of the most widely distributed exotic fish species worldwide. Together with A. ambassis, they have become the dominant fish species in the St Lucia estuarine lake since the closure of the mouth in 2002 and are, therefore, a crucial component of the food webs throughout the system. After a decade dominated by dry and hypersaline conditions, the St Lucia system has changed dramatically in terms of prevailing environmental conditions, as a result of higher than average rainfall at the end of 2011 and the onset of a new wet phase at the start of 2012. In response, A. ambassis, which prefers lower salinity regimes, has expanded its distribution range throughout the estuarine lake. Stable δ¹⁵N and δ¹³C isotope analysis was used in conjunction with gut content analysis to elucidate the diet of these species at sampling localities spanning the geographical range of the system and determine whether these species shift their diet in response to environmental or climatic shifts. From both studies it is evident that from a temporal and spatial scale these two species adopt similar, yet very different, dietary tactics. Oreochromis mossambicus was shown to adopt a generalist feeding strategy, opportunistically feeding on dietary items that are available thus allowing this species to alter its diet according to the environment that it inhabits. Trophic positioning of this species was found to be controlled by salinity in St Lucia as dietary composition differed greatly between sites. In contrast, Ambassis ambassis displayed a more specialist dietary composition, feeding predominantly on zooplankton. However, this species also opportunistically supplements its diet with additional sources when available. Trophic position of A. ambassis was higher in the dry season owing to the increased productivity of the system during the wet season. The success and dominance of both species in the St Lucia system can therefore be attributed to their dietary strategies. Under extreme environmental conditions, O. mossambicus has the added advantage of its wide tolerance of different environmental conditions, particularly salinity, thus allowing it to proliferate.
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    Evaluating the thermal stress response of South African abalone, Haliotis midae, to biogeographical temperature variability.
    (2014) Khuzwayo, Sharon Jabu.; Vosloo, Andre.
    A gradient of sea temperatures is created along the South African coastline by the confluence of the cold Benguela Current on the West coast with the warm Agulhas Current on the East coast. This temperature gradient allows for an assortment of species to occupy the variety of microenvironments occurring in this area. Amongst these species is commercially important South African abalone, Haliotis midae, which although being capable of existing across this wide range of temperatures grows larger on the cooler West coast. Abalone reared on the warmer East coast however, experience greater mortalities especially during the more thermally variable summer months. The aim of the study was thus to assess the zone of tolerance for H. midae by exposing abalone to fluctuating temperatures in an attempt to model environmental temperature instability, a scenario which may likely be worsened by global climate change. Animals from the West and East coasts were exposed to two thermal treatments of fluctuating temperatures with the first group being kept at 16°C±2 and the second group kept at 16°C±4. The control group was maintained at a constant 16°C indicating that the mean temperature experienced by all three groups was 16°C. Oxygen consumption, nitrogen excretion and O:N ratio were assessed at the organismal level to give an indication of metabolic rate, amount of protein excreted and type of metabolic substrate utilized respectively. At the biochemical level, D-lactate accumulation was quantified to indicate whether metabolism was proceeding aerobically or anaerobically. Heat shock protein 70 (Hsp70) expression and degree of carbonylation were analyzed at the proteomic level with Hsp70 also being assessed at the transcriptomic level. All biological responses were measured at days 1, 3, 7 and 14 of the two week exposure. Oxygen consumption rates were significantly elevated on day 14 when comparing treatment group animals to control group animals of the same biogeographic region. P < 0.05 for both treatment groups from the West coast, while P < 0.001 for the East coast treatment groups. The ammonia excretion rates of the West coast animals were significantly lower than those of the controls at day 14 with P < 0.001 for both treatment groups, while ammonia excretion rates were elevated in East coast animals at day 14, although not significantly. Trends similar to those seen for ammonia excretion rates were exhibited by O:N ratios. West coast animals showed lower than control O:N ratios at day 14 (P < 0.01 for both treatment groups) while East coast animals displayed higher than control values (P < 0.05 only for the 16°C±2 group) at day 14. D-lactate, having been detected only for the West coast animals, showed no significant differences but large degrees of variation were noted on days 1 and 7. Carbonylation was evident for animals from both biogeographic regions with baseline carbonyl accumulation for East coast animals being greater (non-significantly) than that of the West coast animals. The hsp70 gene expression remained low for both biogeographic groups with West coast animals appearing to show slight elevations in expression at days 1 and 7, days which also displayed high degrees of variability. The West coast animals appeared to be better suited to coping with the thermal fluctuations, as they not only transiently reduced oxygen consumption rate to reduce ROS production, but also utilized the assistance of the D-lactate pathway possibly to maintain metabolism, both of which were not observed in the East coast animals. Although West coast abalone seemed to have slightly elevated hsp70 expression (suggestive of a repair response) when compared to their East counterparts, both groups of abalone were shown to have incurred notable amounts of protein damage (i.e. carbonylation). This suggests impairments in both protective and repair responses for animals from both biogeographic regions. The lack or attenuation of physiological responses noted in East coast abalone may be due to limitations in thermal adaptation but subsequent studies are required to confirm this notion. The information obtained from this study may assist in providing an insight into the mechanisms responsible for thermal limitation in H. midae and how this species is likely to respond to future periods of thermal instability which may be worsened by global climate change. An understanding of the processes leading up to limitations may potentially assist the abalone aquaculture industry in altering culturing practices early on to support optimal performance in abalone.
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    Spatio-temporal variations of the sedimentology and geochemistry of six estuaries within the eThekwini Municipality, KwaZulu-Natal, South Africa.
    (2014) Pather, Keshia.; Pillay, Deena.
    Estuaries are dynamic features of a coastline whose sediments are influenced by riverine and marine processes. Periodic events such as floods, as well as variations in mouth status, greatly affect the energy levels within an estuary and subsequently the amount of sediment erosion and deposition that takes place. Concurrently, pollutants are transported and deposited into estuaries and can reside in the sediments for many years. The estuaries of the eThekwini Municipality in KwaZulu-Natal, South Africa, are exposed to a variety of pollutants; however with the expanding industrial sector within this region, metal contamination is of concern. This study investigates the sedimentology and geochemical variations of six estuaries within the municipality namely, the uTongati, uMdloti, uMgeni, Isipingo and uMbokodweni estuaries as well as the Durban Harbour. To determine the spatial variations in estuarine sedimentology, sediment cores were collected longitudinal to the estuary axis. The core samples were analysed for sediment colour, texture and organic matter content. To assess the geochemical variations, core samples were analysed for Zn, Cu, Cr, Ni, Pb, As, Fe, Al, Ca, S, P, Mg, Mn, Cd and V concentrations. Some samples were also carbon dated to provide a temporal aspect to the sediment and geochemical variations. Descriptive and graphic techniques were used to examine the sedimentology within the estuaries; and the geochemical data was analysed with the use of multivariate statistics. Additionally, pollution indices and sediment quality guidelines were utilized to assess the pollution levels within the sediments. The results indicated that lower energy environments caused by protracted mouth closures in the uMdloti and Isipingo estuaries accounted for large amassing of fines. In contrast, the accumulation of mixed coarse and fine sediments in the uTongati and uMgeni estuaries was an indication of high fluvial flows and open mouth conditions. All carbon dated ages for all estuaries were greater than 700 years which may be attributed to a combination of scouring effects from past and recent flood events and also possibly due to the deposition of re-worked older sediments from upstream. Low metal concentrations were found within the sediments of all estuaries, and the presence of fines and organic matter governed their concentration variations with depth. The uMgeni and uMbokodweni estuaries which are located immediately downstream of industrial and urban areas, were found to contain relatively higher concentrations of elements Pb, Cu, As and Ni. These metals showed high enrichment within the sediments; however actual concentrations were below sediment quality guideline levels. General pollution levels within all estuaries were very low, and can be attributed to the climatic influences within this region which has a ‘cleansing’ effect on the estuarine environments in removing contaminants.
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    The influence of heterotrophy on the resilience of hard coral Pocillopora damicornis to thermal stress and bleaching.
    (2013) Kisten, Yanasivan.; Glassom, David.; Vosloo, Dalene.
    Global warming from anthropogenic greenhouse gas emissions causes temperature increases in aquatic ecosystems. The rise in environmental temperatures places sensitive organisms under thermal stress. Reef-building corals are a critically important group of animals that provide many ecosystem services for coral reef ecology and the economy and are at a high risk of loss from thermal stress. Thermal stress causes corals to lose their colour, i.e. become bleached, resulting from the loss of symbiont zooxanthellae. This diminishes the energetic benefits that zooxanthellae provide to corals leading to a decline in coral health and high mortality rates. However, corals are also predators and can thus draw nutrients from zooplankton prey to supplement their nutritional requirements. This study investigated whether heterotrophic feeding can ameliorate the effects of thermal stress on coral physiology by providing an alternative energy source to zooxanthellar photosynthesis. Fragmented Pocillopora damicornis coral colonies were exposed to daily maximum temperatures of up to 31°C while being either starved or fed. During the experimental period coral nubbins were monitored for changes in polyp extension, oxygen consumption rate, feeding rate, colour, chlorophyll a content, zooxanthellae density, antioxidant potentials and DNA integrity during stress and after a short recovery period. It was found that, as expected, coral polyp extension, oxygen consumption rate, colour health, chlorophyll a content, zooxanthellae density and DNA integrity were all adversely affected by thermal stress. This indicted that all these measurements were viable biomarkers for assessing the negative effects of thermal stress on coral health. Coral colour, oxygen consumption rate, chlorophyll a content, lipid content, antioxidant potential and DNA integrity were all significantly improved by feeding. These results indicate that feeding does play a role in improving overall coral health and supports the physiological processes in coral tissue during and after thermal stress. The conclusions from this study also have great significance for coral reef ecology and management as predictions of reef resilience can be made from zooplankton ecology and boosting zooplankton availability to corals may be considered to mitigate the harmful effects of thermal stress and bleaching.
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    Ecosystem functioning of selected estuaries on the east coast of South Africa.
    (2013) Cisneros, Kelly Ortega.; Scharler, Ursula Michaela.; Whitfield, Alan Kenneth.
    River inflow is one of the most important factors influencing the density and biomass of estuarine biotic communities. The aim of this study was to obtain an understanding of the ecosystem functioning of selected estuaries on the east coast of South Africa and to represent their dynamics through ecosystem models. The responses of water column nutrients, plankton density and biomass to inlet phase changes for 16 temporarily open/closed estuaries (TOCEs) in South Africa were first determined. This analysis demonstrated that inlet phase and the duration of mouth closure were the most important factors determining plankton density and biomass of the analysed TOCEs. Estimates of planktonic standing stocks for four of these estuaries revealed that stocks can be from 26 to 10 000 times higher during the closed compared to the open phase. Also, slightly higher variability of planktonic density and biomass was recorded during the closed phase of TOCEs. The second major thrust of this study was to analyse the variability and temporal stability of planktonic and macrobenthic invertebrate density and biomass in two KwaZulu-Natal estuaries over a dry/wet cycle. The results suggest that “stable” variability and species synchronization could be the mechanisms whereby the estuarine biota of these systems compensate for environmental changes and attain a degree of environmental homeostasis. The third major thrust involved an assessment of the spatio-temporal variations in the elemental composition and stoichiometry of suspended and sediment detritus, zooplankton and macrobenthic taxa from two estuaries over a dry/wet cycle. Significant seasonal variations in the elemental composition of detritus, zooplankton and macrobenthic species were found, with the variations in the elemental content of sediment and suspended detritus being related to the seasonal changes in river inflow, while the among-taxa variability was mainly explained by feeding mode. Finally, static seasonal carbon and nitrogen ecosystem network models were developed for the East Kleinemonde, Mlalazi and Mpenjati estuaries to investigate their nutrient dynamics and ecosystem functioning. The results indicated that the East Kleinemonde and Mpenjati estuaries were mainly dependent on primary producers during the dry season, especially the high standing stocks of phytoplankton and microphytobenthos. Similarly, the dependency on detritus was higher during the wet season due to the high riverine imports during this season. Consequently, higher detritivory was recorded in all three study systems during the wet season. Cycling of nitrogen was higher than of carbon on a seasonal basis, with higher recycling of nitrogen during the dry season implying a lower availability of this element due to reduced freshwater inflow and nutrient input during the low rainfall period. System indices indicated that the organization of these systems was higher during the dry season, while the overheads on imports and exports peaked during the wet season. The ecosystem models analysed here provide an initial insight into the overall carbon and nitrogen dynamics of estuaries on the east coast of South Africa.