ZOOPLANKTON STANDING STOCK AND COMMUNITY SIZE STRUCTURE WITHIN THE EPIPELAGIC ZONE - A COMPARISON BETWEEN THE CENTRAL RED-SEA AND THE GULF OF ADEN

Standing stock and size composition of the zooplankton comunity (> 100 mu m) were studied in four depth strata of the upper 200 m of the wat er column during a ''Meteor'' cruise to the central Red Sea and Gulf o f Aden in spring 1987. The central Red Sea was divided into a northern area of higher salinity and a less saline southern part. Both areas e xhibited significant differences in zooplankton abundance and standing stock. The latter increased by the ratio 1:2:3 from the northern cent ral Red Sea to its southern part and further south to the Gulf of Aden . For size structure analysis samples were fractionated into three siz e classes (100 to 300, 300 to 500, 500 to 5000 mu m) In the central Re d Sea the smallest size was dominant whereas in the Gulf of Aden the l argest size fraction played a greater relative role than in the centra l Red Sea. This shift in size structure of the zooplankton community f rom the Red Sea to the Gulf of Aden is apparently primarily related to ecosystem difference between both areas, leading to a change in speci es composition. In addition, size reduction of individual species comm on to both seas may be of some significance in the extreme environment of the Red Sea.