Yearly comparison of the planktonic chaetognath community in the Chukchi Sea in the summers of 1991 and 2007

In oceans worldwide, chaetognaths are the second most dominant zooplankton taxa and have vital transfer roles between herbivores and higher trophic organisms. Despite the chaetognath's importance, little is known regarding their ecology in the Chukchi Sea, where recent ice reduction is prominent in the Arctic Ocean. We made comparisons of the chaetognath abundance, biomass, community structure (total length and gonadal maturation) and feeding impacts between the years 1991 and 2007. Within the chaetognath community, Parasagitta elegans was the abundant species, and Eukrohnia hamata only occurred in the southern region in 2007. Yearly differences were detected in chaetognath abundance, biomass, total length and gonadal maturation. All of these parameters were greater and more advanced in 1991 than in 2007. The most prominent yearly differences were in the horizontal distributions of chaetognaths, primarily in the northern region in 1991 and the southern region in 2007. The southern chaetognath populations observed in 2007 were considered to be transported by the Pacific water through the Bering Strait. Because of the differences in the original populations between the Chukchi Sea in 1991 and the Bering Sea in 2007, differences in these two years may be due to regional differences. As the Arctic warms, the horizontal distribution pattern, similar with 2007 in this study, will be more pronounced