|Abstract||The results of investigations from several cruises carried out in Qatari waters between 2017 and 2018 were reported. The species composition, distribution and toxicity of Dinophysis community were examined. A total number of five taxa were recorded with dominancy of Dinophysis caudata followed by Dinophysis miles. Of these, two taxa are the first reports from Qatari waters: Dinophysis mitra and D. acuminata. The cell count revealed that the number of cells rose up from October 2017 toward the end of April 2018. Thirty-two freeze-dried samples were analyzed for Diarrhetic Shellfish Poison (DSP), confirming the presence of Pectenotoxin (PTXs) and Okadaic acid (OA), where toxin concentrations ranged from 0.0080 Ng/mg to 0.52 Ng/mg, respectfully.
A number of physical and chemical parameters were measured. The salinity of water collected ranged between 42.00 ‰ and 38.97 ‰. Throughout the area investigated the temperature ranged from in excess of 34 °C in summer to 20 °C in winter. Nutrient concentrations recorded were relatively low, except in samples collected from industrial effusion. The statistical analysis on the physical parameters, nutrients, and cell counts and species number showed a significant difference between seasons and stations at P < 0.05.