Factors responsible for the sudden outburst of Noctiluca scintillans in the Chennai coastal waters, southeast coast of India – a case study

The paper discusses the factors associated with the sudden outbreak of the nocturnal heterotrophic bioluminescent dinoflagellate Noctiluca scintillans along the Chennai coast. The bloom occurred along a stretch of 16 km following a spell of heavy rain in August 2019. The density of N. scintillans varied from 1000 to 19000 cells/L, with a distinguished distribution pattern. High N. scintillans abundance was recorded at Panaiyurkuppam and Kovalam, with 19000 cells/L and 18000 cells/L, recorded respectively. Adequate nutrients brought by substantial rainfall and a high abundance of the diatom Thalassiosira sp. triggered the N. scintillans bloom. The low wind speed (5 m/sec), lowering of atmospheric temperature (from 24.00 to 31.00°C, 27.5 ± 1.17°C), high rainfall (6 mm within one day), and low sea surface temperature (SST) (from 25.20 to 31.00°C, 29.37± 1.17°C) are probable environmental cues. Local hydrodynamics and the diverging currents governed the presence and dispersion of the bloom in the region.