eNews
#03 2026
New Research Provides Insights into How South Africa’s Offshore Benthic Ecosystems Function
By Jordan Van Stavel, Research coordinator, LTO Ocean Integrated Facility, SAPRI
A recent study published in Marine Pollution Bulletin by Jordan Van Stavel, Lara Atkinson, Juliet Hermes and Tamaryn Morris https://doi.org/10.1016/j.marpolbul.2026.119693 provides new insights into how South Africa’s offshore benthic ecosystems function.
Offshore benthic ecosystems are among the least explored environments globally and remain poorly understood. Epifaunal invertebrates (organisms living on, protruding from, are anchored in, or attached to benthic substrata), play an important role in benthic ecosystems and can serve as indicators of overall health. This study investigated the ecological (functional) roles these epifauna play in maintaining healthy marine ecosystems across South Africa’s western and southern ecoregions. One of few studies of its kind on South African offshore benthic epifauna, and the first to explore the offshore southern ecoregion.
This research drew on six years of Department of Forestry, Fisheries and the Environment (DFFE) research trawl surveys, comprising over 900 sampling stations across 13 biogeographic ecotypes along South Africa’s continental shelf and shelf-edge. Eighty offshore benthic epifaunal species were analysed, including sponges, crabs, sea urchins, various sea stars and other invertebrates. This work formed part of Jordan’s Master’s research.
Traditional biodiversity studies have focused mainly on identifying which species are present and measuring their abundance. While this helps track changes in biodiversity, it tells us less about how ecosystems actually function. For instance, two habitats with the same species might function completely differently depending on what those species actually do in the environment, e.g. filter water, recycle nutrients, build habitat, or scavenge and clean the seafloor. Instead, this study used a biological trait-based approach, scoring each species on nine functional characteristics (traits), including body size, mobility, feeding mode, lifespan, etc. This approach provided a detailed picture of ecosystem functioning across the 13 biogeographic ecotypes, and improved our understanding of how different species contribute to ecosystem resilience. The biological trait dataset for the 80 epifaunal species is openly available through SAEON’s Open Data Platform (https://doi.org/10.15493/SAEON.EGAGASINI.20250311).
Fig. 1. Map depicting the 909 benthic epifaunal trawl stations (small black dots) from which data used in this study were collected onboard the FRS Africana along the western and southern ecoregions of South Africa. Coloured polygons are used to delineate the 13 biogeographic ecotypes along the continental shelf and shelfedge of each ecoregion (SANBI, 2022) and the Exclusive Economic Zone (EEZ) is depicted by the black line.
The study revealed that South Africa’s western and southern offshore ecoregions support distinctly different seafloor communities. Along the western ecoregion, soft sediments influenced by the cold, nutrient-rich Benguela upwelling system were largely dominated by a single long-lived sponge species, resulting in relatively similar ecological functions across large areas. In contrast, rocky reefs and submarine canyons supported a greater diversity of species and ecological roles. Deep shelf-edge were characterised by large scavenging crabs that play an important role in nutrient cycling. The southern ecoregion, influenced by the warmer Agulhas Current, showed greater variation across soft-sediment habitats, while its shelf-edge communities were dominated by larger, long-lived organisms.
Fig. 2. A boxplot showing the ‘within’ ecotypes functional alpha-diversity index values for the 13 ecotypes in the western (blue) and southern (red) ecoregions of South Africa. Ecotypes are represented by the coloured boxes, and the median (middle quartile) illustrated by the solid black line in each box. Whiskers are illustrated by vertical black lines showing the amount of variation in functional alpha-diversity values within each ecotype. Black dots represent extreme outliers exceeding the maximum quartile.
Understanding these functional differences is increasingly important as offshore ecosystems face growing pressures from climate change, fishing, and other human activities. By focusing on the ecological ‘roles’ species perform, we can better assess ecosystem resilience and detect ecosystem change before biodiversity loss occurs.
The findings also have practical value for South Africa’s marine spatial planning and conservation efforts. Protecting habitats that support a wide range of ecological functions helps safeguard the ecosystem services that healthy oceans provide, including productive fisheries, biodiversity, and long-term ocean health.
As one of the first broad-scale assessments of offshore benthic functional diversity across South Africa’s continental shelf, this research fills an important knowledge gap and demonstrates how trait-based ecology can improve our understanding of marine ecosystems. These findings provide valuable information for marine spatial planning, biodiversity conservation and sustainable management of offshore ecosystems that support South Africa’s fisheries and ocean economy.
Acknowledgements
This research was funded through the National Research Foundation (NRF) Postgraduate Scholarships, NRF-SAEON Master of Science bursary, NRF SeaMap Grant 138572 and Nelson Mandela University (NMU) Research Scholarships. We sincerely thank the funders for their support of this research. We extend thanks to the Department of Forestry, Fisheries, and the Environment (DFFE) and the crew of the FRS Africana for facilitating the fieldwork and supporting collection of epifaunal data that made this research possible. We thank Dr. Riesna R. Audh for her valuable assistance with the map visualisations presented in this paper.
