Modelling future scenarios of South Atlantic ecosystems from an end-to-end perspective

Júlia P. Olher 1, Jack Laverick 2, Michael Heath 2, Douglas Speirs 2, Maria A. Gasalla 1

1 Department of Biological Oceanography, Oceanographic Institute, University of Sao Paulo, Brazil; 2- Department of Mathematics and Statistics, University of Strathclyde, UK

Contact: [email protected]

The combined impacts of climate change and anthropogenic pressures on marine ecosystems remain underexplored in the South Atlantic. We implemented the StrathE2E model to assess climate and fisheries effects on the food webs of four South Atlantic marine ecosystems: the South Brazil Shelf (SBS), Saint Peter and Saint Paul (SPSP, Brazil), and the UK Overseas Territories of Ascension (AS) and Saint Helena (SH). Projections from the NEMO-ERSEM biogeochemical model were used under two scenarios (SSP1-2.6 and SSP3-7.0), each driven by two Earth System Models (ESMs; CNRM and GFDL), covering a baseline (2010–2019) and future decades (2020–2069).

Regional parameters were compiled through an extensive literature review. The SPSP implementation is currently in the final configuration phase. For AS and SH, all scenarios project ocean warming and increasing oligotrophy, leading to declines in net primary production (NPP), fish and top predators biomass. In SH, NPP is highly sensitive to upwelling and downwelling: increased stratification under SSP1-2.6 leads to greater productivity losses by the 2060s than under SSP3-7.0. In AS, although NPP is also sensitive to vertical mixing, declines in oceanic nitrate are the main driver of biomass decreases across guilds, with the most pronounced effects under SSP3-7.0 in both ESMs. In the SBS, NPP increases only under the GFDL SSP1-2.6 scenario and declines in the other scenarios, mainly due to reduced nutrient inflows at ocean boundaries.

These shifts affect multiple trophic guilds, particularly phytoplankton, zooplankton, and planktivorous fish. Simulations with reduced fishing effort mitigate some biomass losses for benthos, demersal fish, and top predators, while planktivorous fish remain primarily influenced by climate drivers. Our findings indicate losses in NPP and biomass across guilds, highlighting potential challenges for ecosystem management. We aim for these models to support end-users by offering critical insights into ecosystem responses under climate change projections.

Key-words: Climate change; Ecosystem model; Net primary production; Fishing simulations; South Atlantic; StrathE2E.