Climate warming impacts on diversity and structure of coastal fish assemblages at northern latitudes

Abstract

Coastal marine ecosystems are among the most diverse and productive ocean areas in the world and provide a range of ecosystem services. Yet, coastal biodiversity is understudied as compared to the biodiversity of shelf sea ecosystems. Consequently, this hampers assessments of the resilience of coastal ecosystems to the multiple stressors they are affected by. Moreover, ongoing climate change, which is most severe at high latitudes, causes poleward movements of species, thereby altering the diversity and structure of local species communities. Here, we use 25 years (1995-2019) of demersal trawl survey data sampled along >1500 km of the Norwegian coastline (~62-72 °N), to investigate spatial and temporal variation in fish diversity and the potential effect of climate warming on such variation. The bottom water temperature along the Norwegian coast rose during the study period. Species richness decreased with latitude, and community structure varied along the coast. Following ocean warming, species richness increased in all assemblages and latitudes. This reorganization of fish communities along the Norwegian coast introduces novel interactions which may have implications for ecosystem functioning, resilience, and stability. Ultimately, important ecosystem services in the area, such as fisheries and recreation, may be affected.