Seasonal variability of phytoplankton in a coastal lagoon and adjacent open sea in Pakistan


Abstract: The coast of Pakistan (North Arabian Sea) is under the influence of the seasonal cycle of monsoons, which may result in 2 periods of elevated phytoplankton productivity, one during the north-east monsoon (December-February) and the other during the south-west monsoon (May-September). In the present study, elevated primary productivity in the Miani Hor Lagoon and adjacent open sea off Pakistan was found during the south-west monsoon (May-September) and spring inter-monsoon (March-April). The lowest phytoplankton abundance was recorded in the north-east monsoon period at both collection sites. A total of 65 species of diatoms and 32 species of dinoflagellates were identified in the lagoon. In the open sea, 63 species of diatoms and 23 species of dinoflagellates were present. No significant differences were found in salinity, dissolved oxygen, pH, or nitrite, ammonium, or phosphate concentrations during the different seasons at the 2 sites. Temperature and chlorophyll-a varied significantly (P < 0.001) between the seasons, with temperature being highest during the south-west monsoon period and chlorophyll-a during the spring inter-monsoon period. Diatoms showed a statistically significant positive correlation with temperature and a negative significant correlation with salinity. Further studies are needed along the coast of Pakistan in order to understand the dynamics of phytoplankton in this part of the North Arabian Sea.

Keywords: Seasonal abundance, species diversity, physicochemical parameters, phytoplankton

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