Browsing by Author "Sink, Kerry"

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    Distribution of epifauna in offshore benthic environments along the west and south coast of South Africa
    (2018) Shah, Aliya; Atkinson, Lara; Sink, Kerry; Reed, Cecile
    Marine unconsolidated sediments, such as sand, gravel and muds, constitute the most extensive benthic ecosystems globally. Biological data for these ecosystems are frequently sparse which can hinder the success and implementation of marine management strategies for benthic ecosystems. There are limited studies in South Africa on benthic epifauna. This study investigates the composition and distribution of epibenthic invertebrate assemblages along the west and south coast of South Africa (sampled using depth-stratified demersal trawls) to inform marine environmental management. Sample depth varied from 36m to 899m. Multivariate tools (PRIMER and PERMANOVA+) were used to analyse spatial (west vs south coast) and temporal (2011 vs 2017) patterns in epifauna. This study also investigated an overlap region between the west and south coast. A group average linkage cluster analysis defined biotopes using significant branching (p< 0.05). Biotopes were compared against the 2012 National Biodiversity Assessment (NBA) benthic habitat map to investigate whether epifaunal biotopes identified, align with the existing classification. A significant difference among epifauna between region and depth was found, where the west coast had a higher average number of individuals and species per station. Sympagarus dimorphus and Pelagia noctiluca were characteristic species for west and south coast respectively. Epifauna was found to be significantly different between 2011 and 2017, with a notable increase in the abundance of Crossaster penicillatus in 2017. The majority of the biotopes aligned with the current NBA classification, in particular the Agulhas Sandy Shelf Edge ecosystem type on the south coast and South Atlantic Upper Bathyal and Namaqua Muddy Inner Shelf ecosystem types on the west coast. This thesis contributes to the mapping and description of offshore ecosystem types to inform marine environmental impact assessments, marine spatial planning and marine protected area expansion.
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    Mapping and assessing ecosystem threat status of South African kelp forests
    (2020) Dunga, Victor Loyiso; Bolton, John; Sink, Kerry; Blamey, Laura; Rothman, Mark; Lück-Vogel, Melanie
    At a global scale, kelp forests play a significant ecological, social and economic role through their provision of ecosystem services. South African kelp forests are no exception and recent studies have established their value. To maintain these benefits, informed management is needed. An understanding of kelp forest distribution, ecosystem functioning, pressures, and ecosystem state are key requirements for effective management. The South African National Biodiversity Assessment (NBA) synthesises research to report on the status of ecosystems to guide policy, planning and decision making. Kelp forests were excluded from two previous national assessments, as they were not represented on the National Map of Marine Ecosystem types. This thesis aimed to address this omission by producing a map of kelp forest ecosystem types and conducting the first assessment of their threat status. This study sought to develop a modern method for mapping South African kelp forests to update previous maps developed in the mid-2000s. The novel approach extracts the Vegetation Index from kelp forests using advanced multi-resolution Sentinel-2 (A and B) satellite imagery. Using Geographic Information Systems, spectral bands 4 (RED) and 8 (NIR) (10 m resolution) were utilized to calculate Normalised Difference Vegetation Index (NDVI). An expert-guided trial and error approach was adopted to set the NDVI threshold (-0.2) at a level suitable for detecting both subtidal and surface buoyant kelp to the limits of the Sentinel-2 platform. The results showed that the high resolution and deeper water column penetration of this platform enabled the filling of previous gaps and detect both subtidal and surface protruding kelps at low cost. Additionally, the map includes for the first time, the kelp recently reported to have shifted eastwards along the south coast. A total of 1300 km of kelp forest was mapped and three biogeographical subtypes distinguished. Combining the NDVI threshold method and Supervised Classification yielded satisfactory results and an accuracy of 76%. Sentinel-2 imagery was validated using observational classification from Google Earth, field surveys expert knowledge and previous maps. However, the Sentinel's depth penetration was affected by environmental heterogeneity along this coast. Results confirmed the complexities of retrieving spectral indices from environments with varying turbidity, depths, wave climates and the challenges associated with ground-truthing the expansive marine environment. This study advises comprehensive ground-truthing for the three kelp forest ecosystem types as a fundamental step towards long-term monitoring of South African kelp forests. The method developed advanced application of the NDVI in submerged aquatic vegetation mapping and could be modified to support mapping of other ecosystem types such as seagrasses, other seaweed habitats and inland aquatic vegetation. South Africa's new kelp forest map was then used to facilitate the first ecosystem threat status assessment for South African kelp forests using three criteria from the emerging International Union for Conservation of Nature Red List of Ecosystems (IUCN RLE). To assess threat status, ecosystem extent and condition were considered. Three kelp forest ecosystem types were assessed; namely Namaqua, Cape and Agulhas Kelp Forests and an additional combined single South African Kelp Forest to explore the effect of scale in assessing threat status. Literature was reviewed to develop a conceptual model to support the assessment and define ecosystem collapse. Thirteen relevant pressures were mapped to determine ecosystem degradation across the extent of each kelp forest type using a cumulative pressure mapping approach. Four categories of ecosystem condition were recognized in alignment with the IUCN thresholds for ecosystem degradation. The results of the ecosystem threat status assessment show sensitivity to the different assessment criteria, the scale of ecosystem delineation and assessment approaches. There is no reported reduction in the distribution for any of the South African kelp forest ecosystem types, therefore, the decline in extent under criterion (A) was assessed as Least Concern for all types. For criterion (B) which is related to geographic extent and threat, results were most sensitive to ecosystem delineation with results ranging between Least Concern and Critically Endangered under different sub-criteria and for different ecosystem types. Also, for the criterion (C) which is related to the extent of abiotic degradation, the results ranged from Vulnerable to Endangered under different sub-criteria and for different ecosystem types. Further work is needed to validate kelp forest ecosystem types; consider the implications of multiple scales of classification, mapping and assessment; improve pressure data, groundtruth ecosystem condition, and assess the disruption of biotic processes. In line with the protocols of the IUCN RLE, South African kelp forest ecosystem types appear threatened with plausible results ranging between Vulnerable and Endangered. The accuracy of these assessments can be strengthened by more research to refine conceptual models, calibrate assessments of degradation and better define thresholds of collapsed ecosystems.
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    Marine ecosystem classification and conservation targets within the Agulhas ecoregion, South Africa
    (2022) Nefdt, Leila; Karenyi, Natasha; Griffiths, Charles; Sink, Kerry; Atkinson, Lara
    Deep-sea benthic ecosystems remain poorly studied in South Africa, limiting understanding of community biodiversity patterns and their environmental drivers. This is one of the first studies to (i) visually investigate marine epifaunal community patterns and their environmental drivers along the Agulhas ecoregion outer shelf, shelf edge and upper slope to support marine ecosystem classification and mapping, and (ii) to determine the conservation targets for selected national marine ecosystem types to inform improved management of the marine environment, through Marine Spatial Planning processes. Visual surveys of the seabed were conducted to quantify epifauna during the ACEP Deep Secrets Cruise in 2016, using a towed benthic camera system. Twenty-nine sites were sampled, ranging from 120-700 m in depth and spanning the shelf-slope transition from the western edge of the Agulhas Bank to offshore of the Kei River mouth. A total of 855 seabed images were processed, and 173 benthic taxa quantified. Corresponding environmental variables were used to determine potential drivers of observed biodiversity patterns. Data were analysed using multivariate analyses, including CLUSTER, MDS and DistLM, in PRIMER v6 with PERMANOVA. Ten different epifaunal communities were classified and described with key characteristic taxa identified. Communities found in habitats that comprised mostly hard rocky substrata generally exhibited higher in species richness and were most commonly characterized by stalked crinoids, various corals and bryozoans, whereas communities found in habitats comprising unconsolidated sediment were lower in species richness and commonly characterized by polychaetes, cerianthids and brittle stars. Communities found in habitats comprising both hard and soft substrata had a mix of the above-mentioned epifauna. The distribution of these communities was mostly influenced by substratum type, longitude, trawling intensity, depth, and presence of visible particulate organic matter. The combined interactions of topography, substratum and the unique hydrodynamic conditions along the Agulhas ecoregion shelf-slope transition are likely responsible for the observed patterns. The observed community patterns were also compared to the existing classification of marine ecosystem types from the 2018 National Biodiversity Assessment. Fine-scale heterogeneity was revealed within the examined marine ecosystem types, particularly with substratum type and associated community variability and should be recognized and incorporated into future iterations of the national marine ecosystem classification and map. Species-area curves were used to calculate conservation targets for three ecosystem types, defined by the 2018 National Biodiversity Assessment, namely the Agulhas Coarse Sediment Shelf Edge, South West Indian Upper Slope, and the Agulhas Rocky Shelf Edge. Considering the epifaunal species richness (using the bootstrap estimator) and area, per image and per ecosystem type, the rate of accumulation of species was calculated and used to estimate the percentage of species expected to be represented by any given percentage of protected ecosystem type area. Between 20 and 30% of the area within these ecosystem types will need to be protected to represent 80% of the species. This study has shown that an integration of environmental parameters together with biodiversity measures to better understand and classify offshore benthic ecosystems has worked well. However, to improve the resolution of the national marine ecosystem classification and map, there needs to be greater input of fine-scale biological and environmental sampling and mapping of substratum types across the Agulhas ecoregion shelf-slope transition zone. This work is contributing to improvements in the national marine ecosystem classification and map and hence the spatial assessment and planning processes that rely on these products.