Functional diversity of copepod communities in the north-western Barents Sea

Trait-based approaches offer a powerful alternative to traditional species-centred methods by offering a mechanistic understanding of complex ecosystems. This study investigates the functional diversity of copepod communities in the north-western Barents Sea with a focus on trait distribution, trade-offs, and the influence of local environmental conditions across latitudinal and depth gradients. Despite the ecological importance of copepods, the Arctic remains poorly characterized in these respects. To address this knowledge gap, we analysed the spatial diversity of copepods and identified potential trade-offs among three functional traits: body size, feeding strategy, and lipid content. Using community-weighted means, variances, and Redundancy Analysis, we examined trait-environment relationships across bioregions and depth layers in a shelf area expanding from warmer ice-free waters in the south to colder seasonal ice-covered waters in the north and into the basin. Our findings reveal distinct trait distributions: the region south of the Polar Front in warmer waters, copepods tend to be smaller, lipid-poor and predominantly particle feeders, characteristic of a detritus-based food web with higher trait variability. In contrast, the Arctic Shelf and Arctic Basin regions are dominated by larger, lipid-rich copepods with lower trait variances, reflecting strong environmental filtering. Ambush feeding is the prevalent strategy in surface waters across the transect, whereas cruise feeding and a high proportion of wax esters relative to total lipids are primarily observed in the deeper layers. This research enhances our understanding of the functional complexity of Arctic mesozooplankton communities and provides a baseline for predicting future potential regime shifts.