Regional warming changes fish species richness in the eastern North Atlantic Ocean

Regional warming causes changes in local communities due to species extinctions and latitudinal range shifts. We show that the species richness of fish in 3 regional seas in the eastern North Atlantic Ocean has changed over time (1997 to 2008), and we relate this to higher water temperatures and the biogeographic affinity of the species. In the North and Celtic Seas, species richness increased due to increases in the number of warm-favouring Lusitanian species. In the area west of Scotland, species richness decreased because the number of cold-favouring Boreal species decreased. Additional analyses of trends in fishing effort imply that the observed changes in species richness are unlikely to have been induced by fisheries in the North and Celtic Seas, thereby strengthening the idea that climate change affects species richness of marine fish. However, in the area west of Scotland, a potential effect of fisheries in addition to temperature change on the observed change in species richness could not be ruled out.