COMMUNITY STRUCTURE AND VERTICAL-DISTRIBUTION OF CYCLOPOID COPEPODS IN THE RED-SEA

The species abundance and vertical distribution of cyclopoid copepods was analyzed in the central Red Sea (21°N) during winter 1981, and in the northern Red Sea (24°N) during autumn 1980. The results are compared with data obtained in the central Red Sea during autumn 1980. Samples were taken with a multiple opening and closing plankton net with 0.1-mm mesh size to a depth of 450 m. Seasonal variations between autumn and winter were mainly confined to the epipelagic zone (0 to 100 m), while the cyclopoid fauna of deeper layers remained fairly constant during both seasons. In general, cyclopoid diversity and the numerical abundance of many epipelagic species increased during winter. There was, however, a significant decrease in the abundance of Oithona simplex, which had been the dominant cyclopoid during autumn. Seasonal differences in the vertical distribution and diurnal vertical migration behaviour are mainly related to weakening of the strong, seasonal, thermocline. A somewhat lower percentage of carcasses was observed for most species during winter. Regional differences in cyclopoid diversity between the central and northern Red Sea during autumn were minor, but the abundance of many species decreased significantly in the north due to the more extreme environmental conditions. Paroithona sp., however, seemed well adapted to conditions in the northern area, as judged from their higher standing stock. The population centres of several mesopelagic species showed a conspicuous downward shift, by ca 100 m in the northern area, that corresponded to the regional variation in the depth of the oxygenminimum layer. The results are compared with published data on spatio-temporal differences of zooplankton in the Red Sea. © 1990 Springer-Verlag.