Phytoplankton community structure of a mangrove habitat in the arid environment of Oman: The dominance of Peridinium quinquecorne

Little is known about the physical, biological and chemical oceanographic conditions of Oman's Avecenia marina dominated coastal mangrove ecosystem. This study provided information on the phytoplankton community structure and biomass (Chla) and their variability in relation to chemical and physical changes in the coastal mangrove ecosystem of Bandar Khyran Bay. Monthly assessments of phytoplankton and (chlorophyll a) accompanied by CTD and nutrient measurements were carried out at one station from January 2001 to December 2001, Chla were moderately low throughout in all probability due to the high water temperatures, low nutrient concentrations and high turbidity as well as the absence of diatoms in the phytoplankton community. The contribution of net phytoplankton >20 jim to total biomass was minimal throughout the study period except during December where it accounted for 53% of the total biomass. Phytoplankton populations within the size range of 0.74-<5 jim accounted for the highest biomass, followed by the size fraction (5-20 jim). A total of 25 net phytoplankton taxa were identified during the study. The overall composition of the community did not show any marked seasonal variations. The net plankton was dominated by a single species of dinoflagellate Peridinium quinquecorne Abe, 1927 throughout the year comprising more the 90% of the species counts where at times it reached bloom proportions. It has been hypothesized that ability of this species to thrive under a range of physical and chemical conditions allows it to survive and outcompete most other phytoplankton species including diatoms.