Projecting biomass declines in the St Helena Marine Protected Area food web due to climate change

Understanding marine ecosystem responses to climate change is crucial for developing ecosystem-based adaptation strategies. We applied the StrathE2E model to assess climate change impacts on the food web of the St Helena marine protected area (SHMPA). The model was parameterized using two Earth System models (GFDL, CNRM) and two future climate scenarios (SSP1-2.6, SSP3-7.0) from the NEMO-ERSEM model for a baseline period (2010–2019) and future decades up to the 2060s. The SHMPA will become warmer and more oligotrophic, leading to declines in primary producers, fish, and top predators. Despite quantified uncertainty, the direction of change was consistent, with larger declines in CNRM than GFDL. Net primary production is highly sensitive to upwelling and downwelling, with greater stratification under SSP1-2.6 than SSP3-7.0, causing stronger productivity losses. This study presents the first food web model with ecosystem-level assessment of climate change on SHMPA. The projections suggest potential for profound ecosystem-wide transformations posing management challenges.