The distribution and some features of the biology of the ghost shrimp Nihonotrypaea japonica (Ortmann, 1891) (Decapoda: Callianassidae) from the Volchanka River estuary (Vostok Bay, Sea of Japan)

In August and October of 2013, the patterns of the spatial distribution, size, and sex composition of the estuarine population of the ghost shrimp Nihonotrypaea japonica were studied in the Vostok Bay (Peter the Great Bay, Sea of Japan) for the first time in Russian waters. It was found that this species inhabits waters under monthly mean temperatures from −1.6 to 21.7°C and salinity from 11.2 to 32.5‰, populating silted sand below the ice cover that is typical for December-March. The maximum population density of N. japonica reached almost 200 ind./m 2 , and a biomass of 120 g/m 2 with average values of these parameters of 18 ± 43 ind./m 2 and 10.83 ± 25.50 g/m 2 , respectively, which is almost one-third of the total biomass of the macro-zoobenthos. The population consisted of males with body lengths of 14–61 mm and females from 17 to 58 mm. In the size composition four groups of individuals were distinguished: underyearlings, 1-, 2-, and, apparently, 3-year old animals. The male/female ratio is close to 1 : 1.2. Males prevailed in animals with body lengths of less than 20 mm, while females prevailed among larger individuals. Features of the spatial distribution, size, and sex composition of populations of N. japonica are discussed in relation to the environment and reproduction at the northern boundary of its range.