Long-term changes in Summer zooplankton communities of the Western Chukchi Sea, 1945–2012

Abstract

The Chukchi Sea pelagic ecosystem, which is finely tuned to the region’s seasonal ice formation and retreat, has been undergoing dramatic oceanographic change related to shifting sea ice cover and increasing temperatures over the last decades. We examine historical data sets on zooplankton communities in the central Chukchi Sea during the time period 1946 to 2012. Analysis is confounded by differences between years in terms of spatial coverage, seasonal variability, and methodology; nonetheless, trends remain detectable when a sufficient number of study years is compiled. In addition to high levels of interannual variability, we demonstrate that there have been significant increases in zooplankton biomass and abundance in recent years compared to historical studies, along with shifting distribution ranges for several key species. This signal is most pronounced for the copepods, particularly Calanus glacialis, which appears to be indirectly benefiting from warming of the region. While summer zooplankton communities of the Chukchi Sea have been primarily Bering-Pacific in character for as long as records exist, continuing warming and ice loss are increasing the influence of Bering-Pacific fauna within the Chukchi region.