Baseline assessment of Benthic Invertebrate Communities in the Southern Benguela: insights from Table Mountain National Park MPA, Robben Island MPA, and the seas of Good Hope EBSA

Abstract

Areas afforded protection in the ocean space, for example, Marine Protected Areas (MPAs), assist in managing the marine environment by promoting fisheries sustainability, ensuring that marine ecosystems function effectively, and serve to protect the range of species living there. For these areas, baseline information is key in order to determine the range of organisms inhabiting these spaces. The aim of this thesis was to gain a better understanding of the benthic macro-invertebrate fauna of the southern Benguela ecoregion in South Africa, with a focus on the Table Mountain National Park Marine Protected Area (TMNP MPA), Robben Island Marine Protected Area (RI MPA) and the Seas of Good Hope Ecologically or Biologically Significant Area (EBSA). A comprehensive benthic survey was conducted from August to September 2019 to provide baseline information of the macro-benthic invertebrate fauna, including their diversity, assemblage patterns and the environmental variables that influence them. This study focussed on the visual assessments using two different camera systems: a simple Drop camera and a towed camera (Ski-Monkey). A total of 48 stations were sampled and imagery software was used to analyse representative images per station. The habitat characteristics and species abundance of both hard and soft bottom substrata were recorded. Diversity indices selected for analyses and interpretation of data included species richness (S), abundance (N), Pielou’s evenness index (J’), which measures diversity along with species richness and the Shannon-Weiner diversity index (H'), measuring the diversity of species in a community. The species accumulation curves for the study area did not reach an asymptote, indicating that further sampling could reveal additional species and enhance the overall understanding of the area's biodiversity. Despite the latter, we have used the best available data from the survey to provide a better understanding and provide baseline information for the sampling areas. These data, while not exhaustive, offers valuable insights into macro-benthic invertebrate communities and serves as an important foundation for future research and conservation efforts in the southern Benguela ecoregion. The drop camera sampled a higher mean percentage cover of benthos and rock, and a lower percentage of sand compared to the ski-monkey. The significantly higher percentage cover of sand in the Ski-Monkey samples is expected since a towed camera system is better suited for use on soft sediment. The mean species diversity from images collected by the drop camera (i.e. richness, abundance, percentage cover, evenness), compared to that collected by the Ski Monkey were found to be significantly different (P < 0.05) with the Ski-Monkey being the higher of the two. Large variations in diversity were found between the samples. Community structure was analysed and differences in community structure were found to be related to depth and substrate type. Findings from this study has provided an important overview of the region's biodiversity, revealing a diverse range of species, shedding insight on diversity and community structure and providing a strong foundation on which to build future research efforts. Significant differences were found in species richness, diversity, and abundance between camera systems. When comparing sampling effort between the two camera systems, images collected by the Ski-Monkey captured a higher species richness, diversity and abundance compared to the Drop camera system. The study showed that the southern Benguela ecosystem is heterogeneous and the distribution of organisms varied spatially according to substrate type, location and depth. These results are important for MPA conservation and management, as well as for understanding benthic invertebrate diversity and abundance in the region. The study provides valuable baseline information for future research and highlights the need for continuous monitoring of the protected areas in the southern Benguela ecoregion. The high concentration of endemism and restricted species in the South-Western Cape is further highlighted by the lack of alien species in the research area, emphasizing the significance of protecting these ecosystems against invasive species. Baseline data on the benthic invertebrate fauna, related habitats, and environmental factors affecting their distribution and abundance in the southern Benguela ecoregion have been supplied by this thesis. The two environmental factors that have been found to best explain the observed community patterns are substrate type and depth. The adoption of long-term monitoring systems and the application of standardized efforts to guarantee the efficacy of conservation initiatives are among the recommendations for future research. Overall, this study makes a substantial contribution to our knowledge of the benthic ecosystems in the southern Benguela ecoregion and offers insightful data for the preservation and management of the marine biodiversity in the area. The findings of this research will also help shape decisions on marine spatial planning, which will support South Africa's efforts to preserve and manage its marine environments sustainably.