Three decades of increasing fish biodiversity across the north-east Atlantic and the Arctic Ocean

Observed range shifts of numerous species support predictions of climate change models that species will shift their distribution northwards into the Arctic and sub-Arctic seas due to ocean warming. However, how this is affecting overall species richness is unclear. Here we analyse scientific research trawl surveys from the North Sea to the Arctic Ocean collected from 1994 to 2020, including 193 fish species. We found that demersal fish species richness at the local scale has doubled in some Arctic regions, including the Barents Sea, and increased at a lower rate at adjacent regions in the last three decades, followed by an increase in species richness and turnover at a regional scale. These changes in biodiversity paralleled an increase in sea bottom temperature. Within the study area, Arctic species’ probability of occurrence generally declined over time. However, the increase of species from southern latitudes, together with an increase of some Arctic species, ultimately led to an enrichment of the Arctic and sub-Arctic marine fauna due to increasing water temperature consistent with climate change. Significance Statement Global modelling studies suggest increased species arrivals from lower latitudes and local expirations at high latitudes due to global warming. Our analysis of 20,670 standardized scientific trawl surveys with 193 fish species from the north-east Atlantic and Arctic Oceans found an increase in species richness in the region parallel to an increase in sea bottom temperature. Some Arctic species declined in probability of occurrence over time, but some increased. This, together with the increase of southern-latitude species led to an enrichment of the Arctic and sub-Arctic marine fauna attributed to climate change.