Recent warming causes functional borealization and diversity loss in deep fish communities east of Greenland

Aim We assessed temporal trends in functional diversity of the deep‐sea demersal fish communities of East Greenland to characterize ecological responses to rising sea temperatures. Location The study region encompasses a shelf and slope area located offshore between 63°N and 66°N, east of Greenland. Methods A unique dataset of demersal fish abundance covering a depth range of 1500 m over 18 years was combined with a fish trait dataset which included a mix of quantitative and categorial traits that characterized species' morphology, feeding strategy, habitat, and life history. We analysed the species by trait matrix using principal component analysis (PCA). To investigate trait patterns across the communities (sites), community weighted mean (CWM) traits were calculated and analysed using PCA. Further, depth specific and temporal trends in functional diversity indices were calculated. Results We found signs of a taxonomic and functional borealization, associated with a loss in functional diversity, down to 1000 m, characterized by an increase in mobile generalists and a decrease in bottom dwelling benthivores. Main conclusions The increased dominance of boreal species traits was not sufficient to compensate for the loss of Arctic species traits leading to declining functional diversity. The decrease in functional diversity may negatively affect ecosystem robustness to environmental change. These responses are most likely not unique to this study area and call for more attention to ecosystem considerations in climate change management strategies in the deep‐sea.