First report of Protoperidinium steinii (Dinophyceae) bloom from the coastal marine ecosystem - an observation from tropical Indian waters

A dense bloom of Protoperidinium steinii was observed in the backwaters adjoining the western Bay of Bengal, Kalpakkam coast, which might be the first report for the world oceans. The brownish-red bloom appeared on 2 October 2019, and it was monitored on alternate days up to 14 October. Surface water temperature was about 27.5°C and salinity was <17 PSU during the bloom. Dissolved inorganic nutrients like nitrate, ammonia, silicate, and phosphate were extremely high compared to that of the coastal waters. The chlorophyll-a maxima (20.95 mg m−3) coincided with the highest Protoperidinium density (113.9 × 104 cells l −1). The contribution of P. steinii ranged from 17−93% of the total phytoplankton population. Since P. steinii is a heterotroph and voracious grazer, low autotroph density was observed during the bloom. No mass mortality of fish or other organisms was observed, thereby indicating the nontoxic nature of the bloom