Seasonal fluctuations of phytoplankton community and physico-chemical parameters of the north western part of the Red Sea, Egypt

Abstract Phytoplankton community structure and some environmental parameters in the coastal water of the north western part of the Red Sea were studied seasonally during 2013. A total of 145 species were recorded with clear dominance of Bacillariophyceae, which formed about 76.4% of the total phytoplankton counts with annual average of 3654 cell/L and Dinophyceae (14.63%) with annual average of 700 cell/L. Other algal classes; like Cyanophyceae, Chlorophyceae, Euglenophyceae and Silicoflagellates sustained low counts, forming collectively about 9.0% of the total abundance of phytoplankton. Autumn was the most productive season recording an average of 5916 unit/L, followed by spring (average of 5282 unit/L) and winter (average of 4329 unit/L), while summer showed the lowest counts (average of 3607 unit/L). The species diversity fluctuated between 3.36 in the summer and 3.97 in autumn, with an annual average of 3.76. The physico-chemical properties of surface water exhibited seasonal and spatial variations. The dissolved nitrate (0.07–2.27 μM), ammonium (1.82–8.80 μM), reactive silicate (0.41–5.22 μM) and water salinity (39.9–42.9‰) were the most effective factors that controlled the seasonal fluctuations of phytoplankton during 2013. The multiple regression model was: phytoplankton counts = 28,564 + 0.69 NO 3  + 0.284 NH 4  − 0.13 SiO 4  − 0.30 Salinity (M.R. = 0.91, N  = 24 and p