Zaib-Un-Nisa Burhan

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 (4.5×103 cells/L), P. micans (1.1×103 cells/L), P. gracile / P. sigmoides (2.5×10 2 cells/L) and P. donghaiense (6.6×103 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.

Diatom Species Composition and Seasonal Abundance in a Polluted and Non-polluted Environment from Coast of Pakistan

Diatoms species composition and their seasonal abundance was analyzed at two stations (St. A, 24°49.77〲N 66°57.85′E and St. B, 24°47.93′N 66°58.87′E) of Manora Channel, coastal waters of Karachi, northern Arabian Sea bordering Pakistan. Samples were collected bimonthly from May 2002 to July 2003 and examined using inverted microscope. There was no significant variation observed between species composition at both A and B stations. Distribution pattern and seasonal variations in cell abundance of dominant,abundant, frequent and rare species were observed in which seven dominant species were recorded from station B and six dominant species from station A. Among both centric and pennate diatoms, the genera Chaetocerose affine, Pleurosigma sp 1, Thalassiosira sp, Navicula directa and Nitzschia longissima, Rhizosolenia setigera, Thalassionema nitzschiodes remain dominated all year although seasonal variations in their cell abundance were observed for these species. Statistical analysis showed that most of the dominant species were positively correlated with the salinity and temperature at both stations A and B. It suggests that temperature and salinity are the most significant factors that giveshape to the diatom community and control the community changes. Dominance of pennate species over centric types with high abundance of these pennate species showed that they have better tolerance against pollution and other environmental variables.