Sensitivity of plankton assemblages to hydroclimate variability in the Barents Sea.

Warming, loss of sea icea and changes in ocean currents in the Arctic has led to biochemical changes in pelagic systems that propagate into, and disrupt the Arctic food web. The responses of plankton to environmental variability is critical in understanding how climate change may shape the structure of pelagic ecosystems in the Arctic. To further this understanding, we used a partial canonical correspondence analysis on remotely sensed and modelled hydroclimate together with plankton abundance data from the Continuous Plankton Recorder Survey from the Barents Sea in the European Arctic – one of the fastest warming regions globally – to assess the spatial and interannual variability of plankton community assemblages. The hydroclimate explained ~50 % of interannual variability in species assemblage of plankton communities. Calanus spp. copepod abundances were particularly sensitive to changes in the hydroclimate, which were strongly associated with the mixed layer depth and nutrient concentrations. In warmer years, where SST exceeded those predicted under various future climate scenarios, we saw evidence of thermal stratification of the water column that supported populations of appendicularians, and the potentially toxin-producing diatom Pseudo-nitzschia. Spatial variability of the assemblage was strongly associated SST and salinity gradients that reflect different water masses. Such changes to plankton assemblages in response to hydroclimatic variability are likely to impact trophic interactions with associated organisms, many with ecological and economic significance in Barents Sea food webs