Species traits and CWM data: Recent warming causes functional borealization and diversity loss in deep fish communities east of Greenland

Aim: We asessed whether functional turnover in east Greenland fish driven by increased occurrence of boreal species compensates for the climate-driven loss of species thereby maintaining functional diversity and ecological function. Location: The study region encompasses a shelf and slope area located offshore between 63° N and 66° N, east of Greenland. Methods: We investigated spatio-temporal changes in fish communities based on a unique dataset covering a depth range of 1500m over 18 years combined with a demersal fish trait dataset. We analyzed 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. The CWM traits matrix was further analysed by redundancy analysis (RDA) with depth-strata and year as explanatory variables. Results: We found signs of a taxonomic and functional borealization, associated with a loss in functional diversity, down to 1000m, characterized by an increase in mobile generalists, and a decrease in bottom dwelling benthivores. The functional turnover brought about by boreal species was not sufficient to compensate for the loss of Arctic species traits, hence the loss in functional diversity. Main conclusions: The functional turnover brought about by boreal species was not sufficient to compensate for the loss of Arctic species traits that may negatively affect ecosystem robustness to environmental change. These observations are most likely not unique to this study area, and calls for the inclusion of the deep sea in climate adaptation of management strategies.For use and publication of these data, the authors must be contacted