Species composition and abundance of dinoflagellates from the coastal waters of Pakistan

Objective:To assess the community structure,seasonal dynamics of dinoflagellates population with environmental conditions in the nutrient-rich and polluted coastal waters off,Karachi.Methods:Sampling sites were located from Karachi harbour(Station A)and Mouth of Manora Channel(Station B).Total 180 replicate samples were collected at 1-m depth through Niskin bottle sampler(1.7 L)and fixed with 2%lugol’s preservative then examined under light inverted microscopy,scanning electron and epiflourescence microscope.Results:The environmental conditions,such as temperature[(20-27)°C],salinity[(35-40)psu],chlorophyll a[(1-103)μg/L],pH(6.03-8.13)and dissolve oxygen[(0.7-5.5)mg/L]were recorded from both stations.A total of 96 species were identified into potential harmful toxic/non-toxic bloom forming species and cysts producer.Total dinoflagellate cells between two coastal sites were much concentrated at the adjacent area of mouth of Manora Channel compare to harbor site.The dinoflagellate cell concentration ranging from 20 to~55000 cells/L and the maximum values observed in two season,(~55000 cells/L)in autumn and(~3000 cells/L)in winter season.Gyrodinium sp.was the predominant taxa with the maximum abundance(48166 cells/L)observed in autumn season following by Scrippsiella trochoidea(1200 cells/L),Alexandrium ostenfeldii(3000 cells/L)in winter season,and Ceratium furca(640 cells/L),Protoperidinium steinii(780 cells/L),Ceratium fusus(906 cells/L),Pyrophacus steinii(840 cells/L),Gonyaulax spinifera(666 cells/L),Alexandrium tamarense(520 cells/L)and Dinophysis caudata(393 cells/L)in summer and spring season.Statistically,abundance of dinoflagellates correlated significant to chlorophyll a with chlorophyll a and temperature but inverse relation to salinity and pH observed from both sites.Conclusions:The present study reports on the prevalence and significance of harmful algae bloom forming taxa in the area which would be available for the coastal zone managers and fishery industry to inform them of possible threat and damage that can be caused by any blooms to,for example,fishery industry,and environmental and human health.