Marine Heat Waves Are Transforming Western Mediterranean Marine Ecosystems

We investigated ecosystem impacts of marine heatwaves (MHWs) in the Western Mediterranean Sea using a spatially explicit food-web model. Our simulations suggest that declining biomass trends observed over the past decades in the Western Mediterranean driven by long-term ocean warming and fishing pressure have been exacerbated by the occurrence of MHWs. A north–south dipole in biomass rate of change emerged in response to MHWs: while the northern region displayed positive or neutral responses due to MHWs, the south, particularly the Alboran and Algerian seas, experienced negative impacts. Benthic producers and commercially important species (pelagic and demersal fish and invertebrates) were particularly affected, leading to catch reductions exceeding 10%. We identify previously unreported vulnerable groups and regions, supporting the use of ecosystem models in guiding adaptive management for the future. The increase in intensity and extension of MHW with time suggests that larger effects may be expected in the future.