MICROPLANKTON COMMUNITY WITH EMPHASIS ON POTENTIALLY BLOOM FORMING SPECIES OFF OF HUB DELTA IN THE COASTAL WATERS OF PAKISTAN, NORTHERN ARABIAN SEA

Harmful algal blooms recognized globally to affect marine ecosystem. Substantial studies have been carried out to record phytoplankton community from coastal waters of Pakistan. Of these studies, very few have reported the occurrence of potentially harmful and bloom forming species. Owing to the paucity of research, microplankton community composition and abundance were determined at three stations of increasing distance offshore in coastal waters off the Hub delta, Karachi in the northern Arabian Sea, Pakistan. A total of 46 different microplankton species were observed, including 16 diatoms, 9 dinoflagellates and 21 ciliates species. Nine species of ciliates were recorded for the first time from Pakistan waters. The mean abundance of microplankton ranged from 2160-15690 cells L-1. The bloom forming diatoms Cylindrotheca closterium and toxic Pseudo-nitzchia cf. pungens were the most abundant species. Red tide ciliate Mesodinium rubrum was also observed during the survey. This study is aiming to report initial baseline data on microplankton diversity with emphasis on presence of potentially harmful bloom forming microplankton species off the Hub deltaic region in Pakistan coastal waters. Further studies are recommended to assess the seasonal trend of the microplankton population, particularly with respect to toxic species and their potential impact on human health.