General features of seasonal and interannual dynamics for the zooplankton community in the Amur Bay (Peter the Great Bay, Japan Sea)

Abstract

Species composition, spatial structure, and seasonal and long-term variability of the zooplankton community in the Amur Bay are considered on materials of its two-decade monitoring. Influence of the environments variations on zooplankton is analyzed and the principal aspects of the community functioning are discussed. Two different species groupings of zooplankton are distinguished within the bay, generally in the limits of the pre-estuarine and marine coastal water masses. Small-sized copepods compose the bulk of zooplankton community in both zones, but either Acartia aff.clausi and Oithona brevicornis (in the pre-estuarine waters) or Oithona similis, Pseudocalanus newmani, and Paracalanus parvus (in the marine coastal waters) dominate in dependence on salinity. Nine biological seasons are revealed within the annual cycle of zooplankton succession; species composition and total abundance of the community change crucially with the seasons change. Strong links of interannual variations of zooplankton with thermal or saline conditions are not found, but the portion of allochthonous species fluctuates in direct correlation with the summer monsoon intensity, that is better visible in decadal scale. The deep-water species (Sagitta, large-sized copepods as Neocalanus plumchrus and Calanus glacialis, subtropical species as Calanus pacificus and Paracalanus parvus, and some other species) could be transported into the Amur Bay with the wind-induced water circulation both at the sea surface and at the bottom, in dependence on the species and depth of their aggregations. In climate scale, a tendency to increasing of zooplankton abundance prevails recently due to local species, that is conditioned by separating of high-productive coastal waters from the deep-water sea caused by the cross-shelf exchange weakening with weakening of monsoon winds.