Modelling the pelagic ecosystem service losses from climate-driven declines in phytoplankton

Plankton monitoring surveys inform indicators of Good Environmental Status (GES) for pelagic habitats in OSPAR and UK Marine Strategy biodiversity assessments. These indicators reveal that pelagic habitats in the Northeast Atlantic are not in GES, likely driven by climate change and direct human pressures. By understanding the societal consequences of not meeting GES, policymakers are better guided when implementing management measures – a key aim of ecosystem-based management. To do this, it is first necessary to make direct links between plankton ecological changes and ecosystem service availability.

Here, we project changes to two vital pelagic ecosystem services, carbon export and fisheries, with future plankton ecological changes. We coupled an empirical approach based on pelagic size structure (the relative biomass of large and small organisms), coupled to projections from two Earth System Models to estimate changes in the supportable biomass of fish and in carbon export efficiency under CMIP6 high emissions scenarios. Our projections show that future reductions in phytoplankton biomass and less efficient pelagic food webs, driven by continued global warming, will amplify into substantial decreases in supportable fish biomass as early as 2040-2050. Most alarming is that our projections show the greatest losses to fisheries in Small Island Nations, Southeast Asia and West Africa, regions where fisheries provide vital support to food security and some national economies. Our projections also indicate global decreases to the efficiency of biological carbon export, providing further evidence that oceans will likely have a reduced ability to offset human-induced climate change in the future.