Marine copepod assemblages in the Arctic: The effect of frontal zones on biomass and productivity.

The Barents Sea, as the largest Arctic shelf region with high productivity, supports vital commercial fisheries. The region's ecosystem is significantly impacted by both warm Atlantic Water (AW) and cold Arctic Water (ARW), resulting in frontal zones that delineate differing water masses. Zooplankton populations serve as the primary link between primary producers and higher trophic levels. To evaluate the potential influence of frontal zones on copepods, we conducted a summer survey focusing on sites where diverse water masses interacted. Our findings revealed that species richness, diversity, biomass, and daily production of common copepods were highest in the Polar Front, separating AW and ARW, as well as in the eastern frontal zones (Barents Sea Water and Novaya Zemlya Coastal Water). Herbivorous copepods, such as Calanus spp. and Pseudocalanus spp., dominated in terms of total copepod biomass and production, whereas the small omnivore Oithona similis prevailed by abundance. Multivariate analysis demonstrated a strong correspondence between frontal zones and copepod assemblages. The primary factors explaining spatial variations in copepod biomass and production included the geographic positions of sampling stations, depth, and chlorophyll a concentration. Our research underscores the significance of oceanographic fronts as zones of critical importance for overall pelagic productivity in Arctic regions.