Blooming of Gonyaulax polygramma along the southeastern Arabian Sea: Influence of upwelling dynamics and anthropogenic activities

The influence of upwelling on the phytoplankton community was examined during the upwelling-relaxation period in the southeastern Arabian Sea. Elevated upwelling intensity during the summer monsoon season of 2016 resulted in the re-suspension of harmful dinoflagellates into the surface water. Further, the surplus of phosphorus (P) inputs into the coastal waters from estuarine runoff during the upwelling-relaxation period induced blooming of Gonyaulax polygramma (4.9 × 106 cells L−1). Results from canonical correspondence analysis revealed that elevated upwelling intensity, P and salinity during the year 2016 likely triggered the bloom of G. polygramma in the study region. HABs like G. polygramma threaten fish stocks such as sardines which have a vital role in the ecosystem. Studies on phytoplankton communities and nutrient dynamics in upwelling systems would be useful in predicting the incidence/toxic effects of harmful algal blooms as these regions have a high potential for fisheries. •In the last decade the peak upwelling intensity for the southwest coast of India was observed during 2016.•Increased upwelling intensity re-suspends the harmful dinoflagellate into the surface water column.•Surplus phosphorus input into the coastal waters from estuarine runoff may be responsible for triggering the bloom.