Recurrence of Gonyaulax polygramma bloom in the southeastern Arabian Sea

Gonyaulax polygramma, a bloom-forming dinoflagellate, has been repeatedly observed along the southeastern Arabian Sea in recent years. During our study in October 2021, a patch of reddish-brown water was observed in the nearshore waters off Kannur (southwest coast of India) and later identified as Gonyaulax polygramma using scanning electron microscopy (SEM) and HPLC-based phytoplankton marker pigments. Gonyaulax polygramma accounted for 99.4% of the phytoplankton abundance at the bloom location, with high concentrations of peridinin and chlorophyll-a at the study site. High concentration of SiO42- was observed at the bloom site, while other nutrients were lower than the previously reported values. The bloom of Gonyaulax polygramma also resulted in high concentrations of dimethylsulfide, an anti-greenhouse gas, at the bloom site. In addition to onsite observation, Sentinel-3 satellite data was also used in the detection and validation of the observed bloom using the NDCI index. From the satellite image, it was evident that the bloom persisted at the mouth of the rivers during the study period. Since the red tide of Gonyaulax polygramma has been observed recurrently in the southeastern Arabian Sea, it is proposed to use satellites to detect and monitor the bloom on a routine basis.

Automated summary

Gonyaulax polygramma, a bloom-forming dinoflagellate, has been observed repeatedly in the southeastern Arabian Sea. In October 2021, a reddish-brown water patch off the coast of Kannur, India was identified as Gonyaulax polygramma using microscopy and pigments analysis. The bloom was dominated by Gonyaulax polygramma, with high concentrations of peridinin, chlorophyll-a, and dimethylsulfide. Satellite data was also used to detect and monitor the bloom. Due to its recurrent occurrence, regular satellite monitoring is proposed.