Climate change is affecting ocean temperature, acidity, currents, and primary production, causing shifts in species distributions, marine ecosystems, and ultimately fisheries. Earth system models simulate climate change impacts on physical and biogeochemical properties of future oceans under varying emissions scenarios. Coupling these simulations with an ensemble of global marine ecosystem models indicates decreasing global fish biomass with warming. However, regional projections of these impacts remain much more uncertain. Here, we employ CMIP5 and CMIP6 climate change impact projections using two Earth system models coupled with four regional and nine global marine ecosystem models in ten ocean regions to evaluate model agreement at regional scales. We find that models developed at different scales can lead to stark differences in biomass projections. On average, global models projected greater biomass declines by the end of the 21st century than regional models. For both global and regional models, greater biomass declines were projected using CMIP6 than CMIP5 simulations. Global models projected biomass declines in 86% of CMIP5 simulations for ocean regions compared to 50% for regional models in the same ocean regions. In CMIP6 simulations, all global model simulations projected biomass declines in ocean regions by 2100, while regional models projected biomass declines in 67% of the ocean region simulations. Our analysis suggests that improved understanding of the causes of differences between global and regional marine ecosystem model climate change projections is needed, alongside observational evaluation of modelled responses.

Marine ecosystems provide essential services to the Earth System and society. These ecosystems are threatened by anthropogenic activities and climate change. Climate change increases the risk of passing tipping points; for example, the Atlantic Meridional Overturning Circulation (AMOC) might tip under future global warming leading to additional changes in the climate system. Here, we look at the effect of an AMOC weakening on marine ecosystems by forcing the Community Earth System Model v2 (CESM2) with low (SSP1-2.6) and high (SSP5-8.5) emission scenarios from 2015 to 2100. An additional freshwater flux is added in the North Atlantic to induce extra weakening of the AMOC. In CESM2, the AMOC weakening has a large impact on phytoplankton biomass and temperature fields through various mechanisms that change the supply of nutrients to the surface ocean. We drive a marine ecosystem model, EcoOcean, with phytoplankton biomass and temperature fields from CESM2. In EcoOcean, we see negative impacts in Total System Biomass (TSB), which are larger for high trophic level organisms. The strongest net effect is seen in the high emission scenario, but the effect of the extra AMOC weakening on TSB is larger in the low emission scenario. On top of anthropogenic climate change, TSB decreases by -3.78% and -2.03% in SSP1-2.6 and SSP5-8.5, respectively due to the AMOC weakening. These results show that marine ecosystems will be under increased threat if the AMOC weakens which might put additional stresses on socio-economic systems that are dependent on marine biodiversity as a food and income source.

There is an urgent need for models that can robustly detect past and project future ecosystem changes and risks to the services that they provide to people. The Fisheries and Marine Ecosystem Model Intercomparison Project (FishMIP) was established to develop model ensembles for projecting long-term impacts of climate change on fisheries and marine ecosystems while informing policy at spatio-temporal scales relevant to the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP) framework. While contributing FishMIP models have improved over time, large uncertainties in projections remain, particularly in coastal and shelf seas where most of the world’s fisheries occur. Furthermore, previous FishMIP climate impact projections have mostly ignored fishing activity due to a lack of standardized historical and scenario-based human activity forcing and uneven capabilities to dynamically model fisheries across the FishMIP community. This, in addition to underrepresentation of coastal processes, has limited the ability to evaluate the FishMIP ensemble’s ability to adequately capture past states - a crucial step for building confidence in future projections. To address these issues, we have developed two parallel simulation experiments (FishMIP 2.0) on: 1) model evaluation and detection of past changes and 2) future scenarios and projections. Key advances include historical climate forcing, that captures oceanographic features not previously resolved, and standardized fishing forcing to systematically test fishing effects across models. FishMIP 2.0 is a key step towards a detection and attribution framework for marine ecosystem change at regional and global scales, and towards enhanced policy relevance through increased confidence in future ensemble projections.

A document by Jeroen Gerhard Steenbeek. Click on the document to view its contents.

By evaluating genetic variation across the entire genome, one can address existing questions in a novel way while new can be asked. Such questions include how different local environments influence both adaptive and neutral genomic variation within and among populations, providing insights not only into local adaptation of natural populations, but also into their responses to global change and the exploitation-induced evolution. Here, under a seascape genomic approach, ddRAD genomic data were used along with environmental information to uncover the underlying processes (migration, selection) shaping European sardines (Sardina pilchardus) of the Western Mediterranean and adjacent Atlantic waters. This information can be relevant to the (re)definition of fishery stocks, and their short-term adaptive potential. We found that studied sardine samples form two clusters, detected using both neutral and adaptive (outlier) loci suggesting that natural selection and local adaptation play a key role in driving genetic change among the Atlantic and the Mediterranean sardines. Temperature and especially the trend in the number of days with sea surface temperature (SST) above 19oC was crucial at all levels of population structuring with implications on species’ key biological processes, especially reproduction. Our findings provide evidence for a dynamic equilibrium where population structure is maintained by physical and biological factors under the opposing influences of migration and selection. Given its dynamic nature, such a system postulates a continuous monitoring under a seascape genomic approach that can benefit by incorporating a temporal as well as a more detailed spatial dimension.