Morphotaxonomy and seasonal distribution of planktonic and benthic Prorocentrales in Karachi waters,Pakistan Northern Arabian Sea

Morphotaxonomy and seasonal abundance of dinoflagellates of the genera Prorocentrum and Mesoporos （Prorocentrales） were studied from nutrient-rich waters, Karachi Harbor and the mouth of the Manora Channel, Pakistan during May 2002-July 2003. Using both light and scanning electron microscopy, 13 species of Prorocentrales were identified according to cell shape, size, ornamentation of thecal plates, and architecture of apical platelets, apical pore area, marginal pores, and intercalary bands. P. sigmoides, P. arcuatum, P. scutellum, P. donghaiense, P. balticum, P. minimum, P. emarginatum, P. lima, P. faustiae, and Mesoporos perforatus constitute new records for sindh coast of Pakistan. The most abundant species were P. minimum/P, balticum （4.5x103 cells/L）, P. micans （1.1~103 cells/L）, P. gracile/P, sigmoides （2.5 x 102 cells/L） and P. donghaiense （6.6 x 103 cells/L） at temperatures of 29-31 ~C and salinities of 35-40. Maximum abundance was observed in winter and lower abundance in summer. There was no significant change in the distribution of species between stations except for the benthic species which occurred close to Karachi Harbor waters. Significant positive correlations were observed between Prorocentrum spp. and temperature （R2=0.27） and negative correlations with salinity （R2=-0.32） except for P. minimum and P. emarginatum which has negative correlation with temperature （R2=-0.24） and positive with salinity （R2=0.08, 0.19）. The finding of potential okadaic-acid producing species of benthic Prorocentrum call for monitoring for possible human health problems in this region.

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.