Distribution and some features of biology of the ghost shrimp <i>Nihonotrypaea japonica</i> (Ortmann, 1891) (Decapoda: Callianassidae) from the Volchanka River estuary (Vostok Bay, the Sea of Japan)
The spatial distribution, size and sex composition of estuarine population of the ghost shrimp Nihonotrypaea japonica were studied for the first time in Russian waters in August-October 2013 in the Vostok Bay (Peter the Great Bay, the Sea of Japan). It is found that this species occurs at a temperature range from -1.6 to 21.7°C and salinity from 11.2 to 32.5‰, populating silted sand below the ice coveredge typical for December-March. The maximum population density was about 200 ind./m <sup>2</sup> and biomass 120 g/m <sup>2</sup>. The average density and biomass are, respectively, 18 ± 43 ind./m <sup>2</sup> and 10.83 ± 25.50 g/m <sup>2</sup>, which is one third of the total biomass of macrozoobenthos. The population consisted of males with a body length of 14-61 mm and females 17-58 mm. In size composition there were distinguished 4 groups of individuals corresponding to underyearlings, one-, two- and, apparently, three-year-old animals. The male/female ratio is close to 1 : 1.2. Males prevailed among animals with a body length less than 20 mm, and females among larger individuals. Features of spatial distribution, size and sex composition of populations of N. japonica are discussed in relation to habitat conditions and reproduction at the northern boundary of its range.