Spatial Heterogeneity in Zooplankton Distribution as a Result of Large-Scale Interactions of Water Masses in the Northeastern Chukchi Sea

Interest in the Arctic shelf ecosystem has increased in recent years as the climate has rapidly warmed and sea ice declined. These changing conditions allowed the conduction of large scale surveys aimed at systematic, comparative analyses of interannual variability of the shelf ecosystem. In this study, we compared zooplankton composition and geographical distribution in relation to water properties on the eastern Chukchi and Bering Sea shelves during the summer of 2012 and 2013 as a part of the Arctic Ecosystem Integrated Survey (EIS) program. In 2013, shifts in water mass distribution manifested in a stronger influence of Chukchi Winter and Ice Melt waters, markedly affecting the distribution of expatriate and resident zooplankton species. This pattern was apparent not only in the spatial coverage, but also in their relative abundance and biomass, thus demonstrating the importance of the Arctic community on the northeastern Chukchi shelf. In contrast, zooplankton biomass of Pacific origin decreased in 2013 in the northern Chukchi shelf suggesting a change of its advection pathways into the Arctic. The observed interannual variability in distribution of water properties in the Chukchi Sea shelf is in agreement with previously described systematic oceanographic patterns derived from long-term observation time series. Our study is the first attempt to relate variability in zooplankton distribution in the eastern Chukchi Sea to these oceanographic patterns in the context of changing climatic conditions and to explore potential consequences for the local biotas of the Arctic shelf ecosystem.