Abstract
Spatial variation in the microphytoplankton biomass and diversity as well as the diel variability of the major mesozooplankton taxon, Copepoda was studied with respect to the prevailing hydrographic conditions along the coastal waters of Gulf of Aqaba, Saudi Arabia during the summer period. Conspicuous stratification was evident in the water column while nutrient distribution highlighted the oligotrophic nature of the region. Nitrate showed a notable increase in the deeper layers of almost all the stations and towards the south. Chlorophyll a was low throughout (0.05-0.27 mg m(-3)) though a small peak was observed at a depth of 70m. Diatoms dominated the phytoplankton community in terms of both density and diversity followed by dinoflagellates. A total of 138 phytoplankton species (80 diatoms and 57 dinoflagellates) contributed to the phytoplankton diversity during the study. Zooplankton exhibited clear did variation in distribution with higher abundance during night. Among the thirty-zooplankton taxa observed, Copepoda formed the dominant taxa. Of the total 70 copepod species observed during the study eight species are new records from the Gulf of Aqaba region. The current study also witness conspicuous diel variation of five copepod species within the water column (Acartia negligens, Clausocalanus furcatus, Lucicutia flavicornis, Pleuromamma indica and Haloptilus longicornis).