Abstract
Variations in phytoplankton biomass and diversity in relation to the changing environmental parameters have been studied extensively during the summer season from three different regions (Al Wajh, Duba and Al Khoraeyba) on the northern Red Sea coast of Saudi Arabia. The temperature fluctuated between 25.2 and 31.5 A degrees C with a salinity level between 39.58 and 40.16 PSU. The nutrients did not show any wide fluctuation between the regions and always remained, low which directly influenced the chlorophyll a (0.038-1.87 mg m(-3)). The higher phytoplankton densities were observed from stations A6 to A15 (average 4738 +/- 2351 x 10(3) cells m(-3)) in Al Wajh due to the proliferation of diatom species (Hemiaulus hauckii, Proboscia alata and Thalassiothrix longissima). A total of 283 phytoplankton species was encountered from the whole area (129 diatoms, 152 dinoflagellates and 2 cyanophytes) of which 118 species were new to the Red Sea. Maximum species diversity was observed from Al Wajh (267) followed by Duba (113) and Al Khoraeyba (97). Of these species, 7 diatoms and 20 dinoflagellates have been previously reported to produce harmful algal blooms worldwide.Trichodesmium, which is a dominant diazotrophic genus in the Red Sea, was present at the majority of the stations.