Résumé
Evidence of large-scale biodiversity degradation in marine ecosystems has
been reported worldwide, yet most research has focused on few species of
interest or on limited spatiotemporal scales. Here we assessed the spatial
and temporal changes in the taxonomic and functional composition of fish
communities in European seas over the last 25 years (1994-2019). We then
explored how these community changes were linked to environmental
gradients and fishing pressure. We show that the spatial variation in fish
species composition is more than two times higher than the temporal
variation, with a marked spatial continuum in taxonomic composition and a
more homogenous pattern in functional composition. The regions warming the
fastest are experiencing an increasing dominance and total abundance of
r-strategy fish species (lower age of maturity). Conversely, regions
warming more slowly show an increasing dominance and total abundance of
K-strategy species (high trophic level and late reproduction). Among the
considered environmental variables, sea surface temperature, surface
salinity, and chlorophyll-a most consistently influenced communities’
spatial patterns, while bottom temperature and oxygen had the most
consistent influence on temporal patterns. Changes in communities’
functional composition were more closely related to environmental
conditions than taxonomic changes. Our study demonstrates the importance
of integrating community-level species traits across multi-decadal scales
and across a large region to better capture and understand ecosystem-wide
responses and provides a different lens on community dynamics that could
be used to support sustainable fisheries management.