SURFACE ZOOPLANKTON DYNAMICS AND COMMUNITY STRUCTURE IN THE GULF OF AQABA (ELIAT), RED-SEA

Winter and summer zooplankton maxima were observed on both near-reef and offshore sampling sites in the northern part of the Gulf of Aqaba, with summer maxima smaller than those of winter and more characterized by larval forms. Near-reef zooplankton biomass was generally several times greater than that observed 2 km offshore. During 1987, a near-reef maximum of 155 ind. or 12.2 g wet biomass m-3 was observed in March, while 103 ind. or 8.5 g wet biomass m-3 was observed in July. In the same year, 2 km offshore a maximum of 53 ind. or 2.5 g wet biomass m-3 was observed in February, while a maximum of 33 ind. or 0.5 g wet biomass m-3 was noted in July. The following year, 1988, the near-reef zooplankton abundances were little changed, but offshore zooplankton abundances were much higher (317 m-3). During 1987, the dominant winter (March) forms near the reef were gammarid amphipods, at maximum concentrations of 100 ind. m-3, where the summer (July) maximum was composed primarily of mysids (34 m-3), gammarid amphipods (30 m-3), and fish eggs (24 m-3). The offshore winter zooplankton fauna was characterized by copepods and appendicularians, each at a maximum concentrations of ca 13 ind. m-3, while the summer maximum was dominated by brachyuran zoea (31 m-3). Though the 1988, winter near-reef zooplankton community compositions were similar to those of 1987, the offshore zooplankton fauna was dominated by ostracods, which were relatively rare in previous years. Preliminary data suggests that holoplanktonic forms like chaetognaths, copepods and appendicularians, at an offshore site exhibit different patterns of vertical migration than those near the reef. This different behavior may result from different species compositions of these taxa or from high concentrations of "pseudoplanktonic" bentho-neritic peracarid crustaceans. © 1990 Springer-Verlag.