Известия ТИНРО (Mar 2016)
Mechanisms of subtropical plankton transport into the coastal waters of southern Primorye, a case of <i>Paracalanus parvus</i>
Abstract
Results of long-term studies of zooplankton species in the Amur Bay (Japan Sea) are analyzed. Two seasonal «waves» of the allochtonous species are defined: the first in the early summer that is formed mainly by inter-zonal copepods spawning in the deep layers ( Metridia pacifica , Neocalanus plumchrus, Calanus glacialis ) and the second in the late summer that is represented by warm-water copepods of subtropical origin ( Calanus pacificus and Paracalanus parvus ) obviously transported from the southern Japan Sea by currents. The latter species is able to dominate in the zooplankton community of coastal waters in the early-autumn season. Variations of this mass species abundance in the Amur Bay under changes of wind-driven upwelling/downwelling circulation are investigated using an empirical advective model of its cross-shelf transport. There is found that strong summer southern on-shore winds (summer monsoon) are favourable for its high abundance but in these conditions it is transported toward the coast by the deep compensatory flow developed only after the summer monsoon change to the winter monsoon with opposite direction; that’s why the high abundance is observed in autumn, in September-October. In the years with weak summer monsoon the species is transported to the bay in mass by the surface on-shore wind-driven flow earlier, in August, but its number decreases after the monsoon change, so the maximum of abundance is not high. Patterns of the transport by cross-shelf currents depend supposedly on the depth of plankton concentration. Recent strengthening of summer monsoon causes heightening of P. parvus abundance in the coastal waters at southern Primorye, up to extreme high values in 2013, but climatic trend of the summer monsoon intensity is negative, so decreasing of this species transport toward Primorye coast and its abundance in the coastal waters, as the Amur Bay, can be expected in the nearest future.
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