Vertical distribution and reproductive aspects of caridean shrimps in the deep-water of the East Sea, Korea

Abstract

This study investigates the distributional pattern of the deep-water shrimps in the East Sea. The distribution of the deep-water shrimps showed significant differences by depth. Shallow-dwelling species, Neocrangon communis and Pandalus eous, occurred in the similar ZCM depth but distribution range was widely in N. communis. Of deep-dwelling species, Argis toyamaensis and Eualus biunguis, the latter showed that individuals distributed deepest depth of all species in the East Sea with a narrow depth range. Our observations showed that there were a higher proportion of females in all the depth range except in the case of P. eous, and significant difference between sex ratio and depth was found. In the deep-dwelling species observed the proportion of male was lower than in shallow-dwelling species. A size-related bathymetric distribution was observed for all shrimps. Large size of females and ovigerous female of crangonid species, N. communis and A. toyamaensis mainly distributed at shallow water (300m~400m depth range). But in pandalid species, P. eous, larger individuals of transitional, females and ovigerous females distributed at deep water (700m depth). Also in hippolytid species, E. biunguis, large females and ovigerous females distributed at deep water (800m depth). These results are not consistent with the results of crangonid shrimps. Hemiarthrus abdominalis is an ectoparasite which occurs on the vertical surface of the abdomen of E. biunguis. We observed increased parasites in proportion with increasing host size (10.5mm-15.5mm CL) and proportion of parasitism decreased dramatically over the 15.5mm CL host size. The number of infested females was significantly different by depth, decreased from 700 to 900m depth. Compared with non-infested females in E. biunguis individuals, the body weight of shrimp infested was significantly reduced. Higher percentage of ovigerous females occurred mainly at shallow water depth for both species, N. communis, P.eous during winter season. Ovarian development stages in the both species from 300 to 400m depth was composed dominantly of the spent stage and dramatically decreased by the depth. These results suggest that females have already laid eggs in the shallow depth (300~400m), and ovigerous females migrate to shallow water for hatching. Deep-dwelling species, A. toyamaensis, and E. biunguis had a form different slightly from shallow-dwelling species in winter season. As a whole, these two species did show that ovigerous females were widely distributed in all depth ranges. In case of A. toyamaensis GSI was not significantly different by depths. A. toyamaensis had bigger eggs than N. communis. We suggest that a life-history strategy is determined by many environmental factors by depth in the deep sea, and four species were found the optimal distribution depth that have a close relationship with reproductive strategies.