Composition of plankton community in the summer-autumn period of 2007 and interannual dynamics of zooplankton in the eastern Bering Sea
Biomass of zooplankton was 693-1019 mg/m3 in the eastern Bering Sea in the summer-autumn of 2007, with the maximum in the middle shelf of Bristol Bay and the minimum - in the deep-water part of the Bay. Large-sized fraction prevailed (56-70 %) in the zooplankton both in the shelf and deep-water areas; chaetognats, copepods, and euphausiids presented 80-85 % of this fraction. On the contrary, small-sized fraction dominated (45 %) in the coastal area of the Bristol Bay and medium-sized fraction was the main (43 %) in the shallows at Nunivak Island. Euphausiids eggs and juveniles were abundant in the zooplankton of shallow areas, but copepods dominated both in small-sized and medium-sized fractions. Jellyfishes had significant biomass in the area at Nunivak Island only. Size and taxonomic structure of zooplankton community changed noticeably since 2003. The area of the small-sized zooplankton predominance was wider in 2003 and later till 2005: it included both shallow coastal area and the middle shelf. Species of neritic complex, basically small copepods, prevailed in this widen area. Recently, in 2006-2007, the zooplankton biomass increased in the middle shelf area because of the medium-sized and large-sized fractions shares increasing from 20-45 % to 60-70 %, but the biomass in coastal area decreased, in general. Chaetognats, copepods, euphasiids, hyperiids, and pteropods became more abundant in 2006-2007, but jellyfishes abundance diminished.