First report on the occurrence of Gonyaulax polygramma bloom during the onset of Noctiluca scintillans bloom along the Tuticorin coast, southeast coast of India

Dense and green-coloured patches were encountered on the sea surface waters of the Tuticorin coast on 22^nd October 2022. Microscopic investigation revealed that the discoloration is caused by plankton, green Noctiluca scintillans. In order to find out the causes that trigger the bloom of N. scintillans, plankton samples were collected for 5 days in fourteen days duration from 22^nd October to 4^th November. During the peak bloom period, the abundance and biovolume of N. scintillans reached 1.56 × 10⁴ cells/L and 21.8 × 10¹⁰μm³/L, respectively. The highest concentration (73.65 mg/m³) of chlorophyll-a was recorded during blooming period that was caused by Gonyaulax polygramma and endosymbiont, Pedinomonas noctilucae in N. scintillans. Formation of G. polygramma bloom is being reported for the first time in Tuticorin, southeast coast of India, with a species abundance of 36.9 × 10⁴ cells/L. Present study concluded that besides the optimum hydrological conditions and eutrophic nature of the system, abundant prey (G. polygramma) facilitated the N. scintillans bloom.