The species composition, season of occurrence, and distribution of crab larvae (Decapoda: Brachyura) in the Vostok Bay, Sea of Japan

Abstract

Based on the materials of plankton surveys that were carried out from May to November in 2002, the species composition, season of occurrence, density, and distribution of larvae of the true crabs (Decapoda: Brachyura) from the Vostok Bay, Sea of Japan were studied. The monthly average density of zoeae of this decapod group was low and did not exceed 25 ind./m3. Larvae of 11 species of true crabs were observed. Zoeae of the pinnotherid crab Pinnixa rathbuni, which occurred in the plankton from May to November, absolutely dominated among the crab larvae. Several peaks of the abundance of the early stages of this species were recorded, implying its multiple reproductive periods. In the summer season the ratio of P. rathbuni zoeae ranged from 71 to 96% of the crab larvae; zoeae of this species were the only Brachyura in May and November. Larvae of the remaining ten crab species occurred in low numbers from June to October; the maximum density was observed in August under the highest temperatures. Zoeae of the coastal Hemigrapsus crab species were the subdominant group. The Brachyura larvae mostly concentrated along the western coast of the Vostok Bay. The highest density of larvae (150–160 ind./m3) was observed in the top of the bay, due to the cyclonic circulation of water under the southern wind. The prevailing surface current along the west coast under the southeast and east winds probably carried some of the larvae further south to the Srednyaya Bay, where their density was also significant.