Phytoplankton assemblage and restricted bloom of Merismopedia sp. (Meyen, 1839) in an anthropogenically stressed tropical estuary (Ulhas estuary), India

The present study evaluates the effect of nutrients and their spatio-temporal variation in determining the composition of phytoplankton assemblage. The study recorded the restricted bloom of Merismopedia sp. (Meyen, 1839) in the upstream stations U7 and U8 during post monsoon. The study identified high concentration of ammonia and silicate promoted the proliferation of Merismopedia sp. while salinity and nitrate served important roles in the restriction of this genus to meso-oligohaline region. Shannon-Weiner diversity index as pollution index suggested that mid to upstream of the estuary in post monsoon was moderately polluted, which transformed to marginally polluted in pre monsoon season. The study could identify opportunistic species like Thalassiosira sp. in midstream and Merismopedia sp. in upstream of the estuary which outnumbered and led to low diversity index at these zones.