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South Africa has taken an iterative approach to marine ecosystem mapping over 18 years that has provided a valuable foundation for ecosystem assessment, planning and decision-making, supporting improved ecosystem-based management and protection. Iterative progress has been made in overcoming challenges faced by developing countries, especially in the inaccessible marine realm. Our aim is to report on the approach to produce and improve a national marine ecosystem map to guide other countries facing similar challenges, and to illustrate the impact of even the simplest ecosystem map. South Africa has produced four map versions, from a rudimentary map of 34 biozones informed by bathymetry data, to the latest version comprising 163 ecosystem types informed by 83 environmental and biodiversity datasets that aligns with the IUCN Global Ecosystem Typology. Data were unlocked through academic and industry collaborations; multi-disciplinary, multi-realm and multi-generational networks of practitioners; and targeted research to address key gaps. To advance toward a more transparent, reproducible and data-driven approach, limitations, barriers and opportunities for improvement were identified. Challenges included limited human and data infrastructure capacity to collate, curate and assimilate many data sources, covering a variety of ecosystem components, methods and scales. Five key lessons that are of relevance for others working to advance ecosystem classification and mapping, were distilled. These include (1) the benefits of iterative improvement; (2) the value of fostering relationships among a co-ordinated network of practitioners including early-career researchers; (3) strategically prioritizing and leveraging resources to build and curate key foundational biodiversity datasets and understand drivers of biodiversity pattern; (4) the need for developing, transferring and applying capacity and tools that enhance data quality, analytical workflows and outputs; and (5) the application of new technology and emerging statistical tools to improve the classification and prediction of biodiversity pattern. South Africa’s map of marine ecosystem types has been successfully applied in spatial biodiversity assessment, prioritization to support protected area expansion and marine spatial planning. These successes demonstrate the value of a co-ordinated network of practitioners who continually build an evidence base and iteratively improve ecosystem mapping while simultaneously growing ecological knowledge and informing changing priorities and policy.

South Africa has an extensive coastline offshore of which lies the prominent South African continental shelf, a relatively flat extension of the onshore coastal plain. The continental shelf is host to major mineral and petroleum deposits, home to South Africa’s major sea fisheries and full of navigation hazards. Therefore, knowledge of the seafloor features, or bathymetry, of the continental shelf is essential to understanding both its long-term geological evolution and present-day use for resources and navigation. Unfortunately there has been little advancement in our knowledge of the South African continental shelf since the marine studies of the 1970’s and 1980’s which culminated in the “Bathymetry around Southern Africa” map of Dingle et al. (1987). Although bathymetric mapping equipment and techniques have greatly improved during the last few decades, very little high resolution bathymetric data of the South African continental margin are currently available for scientific use, with the majority of the high resolution multi-beam echo-sounding bathymetric surveys being undertaken by privately owned mineral exploration and mining companies (such as De Beers, Alexkor, Petro SA, Petroleum Agency of South Africa, etc.), the Council for Geoscience and the South African Navy and Hydrographic Office. More recent advances in satellite altimetry have had a major impact on ocean floor bathymetric mapping especially in deep ocean areas where the sea surface generally reflects the underlying bathymetry. The Department of Agriculture, Forestry and Fisheries (DAFF) annually collect single-beam echo-sounding data in order to monitor the abundance of fish species along the South African continental shelf and along with that collect seafloor bathymetry as an additional benefit. The aim of this project is to create a detailed bathymetric map of the continental shelf of South Africa by using digital single-beam echo-sounding data collected by the Fisheries Division of the DAFF over the last two decades. The bathymetric dataset of ±7 million single-beam echo-sounding data points was manually processed, gridded and exported to produce a detailed bathymetric map of the entire South African continental shelf between the Orange River mouth and Kosi Bay complemented by Satellite Altimetry data from the ETOPO 1 – 1 Arc-Minute Global Relief Model (Amante and Eakins 2009) for the deep ocean area adjacent to the continental shelf. The single- beam bathymetric data were collected by the F.R.S. Africana II and F.R.S. Algoa vessels using SIMRAD EKS-38, EK 400, EK 500 and more recently the EK 60 single-beam echo-sounders along with a the SIMRAD ES38B split beam transducer. The West Coast and South Coast margins have the greatest bathymetric detail due to DAFF’s Cape Town base of operations, whilst the East Coast margin is less detailed due to fewer research campaigns in this area. The Bathymetric Map of the South African Continental Margin produced in this thesis reveals several new and more detailed bathymetric features. New bathymetric features include the northern extension of the Olifants Valley submarine canyon, details of the rocky inner shelf related to glacial period sea level lowstands, as well as the coast parallel wave cut terraces and palaeo dune ridges on the middle shelf between Cape Seal and Cape Recife. Other prominent bathymetric features such as Childs Bank, Cape Canyon, Cape Point Valley, the offshore submerged river valleys of the Breede and Gouritz Rivers and the east-west trending, basement anticlinal ridges situated at the southernmost extent of the Agulhas Arch were revealed in greater detail by this study. The underlying geology, physical Oceanography, drainage patterns as well as eustatic sea-level fluctuations can all be linked to the bathymetry of the continental shelf, which is why this thesis examines the influences of each of these factors on the seafloor morphology around the South African coastline.