Projected climate change impacts on the ecosystems of the Agulhas Bank, South Africa

Marine ecosystems are expected to be increasingly affected by climate change, impacting their physical and biogeochemical environment. Changes in primary production, temperatures and hence species distribution, may lead to critical consequences for fishery exploitation. Therefore, future projections are essential to develop sustainable strategies and climate change adaptation plans for fisheries, and fishery-dependent societies. In this study, we focus on the Agulhas Bank, a broad extension of the continental shelf of the South African coast, along which flows the western boundary Agulhas Current. The Agulhas Bank is known for being biologically productive and is an important nursery ground for many commercially exploited fish species, including the chokka squid fishery, a vital source of income for many people in the Eastern Cape Province. Squid catches manifest strong interannual fluctuations, at times causing fishery crashes. Additional impacts due to climate change will have significant socio-economic consequences for this all-important fishery. To investigate future variations of the physical and biogeochemical environment on the Agulhas Bank, we used the global ocean model NEMO-MEDUSA, forced by the high emissions scenario RCP8.5. Our simulations show a significant increase in sea surface temperature and bottom temperature, but limited changes in primary production. Projections highlight an increase in current velocity on the Agulhas Bank throughout the course of this century, induced by an onshore shift of the Agulhas current. This current shift may pose a threat to squid recruitment success as a large fraction of squid paralarvae may be removed from their shelf feeding grounds and lost to the greater ocean via the Agulhas current. The results further show that planktonic food for the paralarvae is less likely to become the main limiting factor in the future, while increasing temperatures may affect growth rates and spawning success.