New record of a bloom forming, genotoxic strain Nodularia strain (KT447209) from Andaman and Nicobar Islands, India

•First report of Nodularia sp. blooms along coastal waters of Andaman Nicobar Islands.•Molecular studies revealed the Nodularia sp. (KT447209) to be a novel strain.•Crude extract exhibited slight genotoxicity against human lymphocytes.•Population of Nodularia crashed at low salinities of ∼12-18‰ during monsoon.•It flourished in summers attaining blooms at salinity >30‰ & SST of 29.5-30.5 °C.

Cyanobacteria blooms in marine waters are limited to only a few taxa; with the genus Nodularia (Nostocales) being one among the most commonly observed and widely studied species. A bloom of Nodularia sp. was observed across a vast area along the coast of the Andaman and Nicobar Islands. The bloom occurred during the summer when salinity was >30‰. This differed to previous reports where blooms have crashed at such high salinities. The molecular phylogeny revealed the Nodularia species to be a novel one. A crude extract from the bloom demonstrated lowed toxicity with an LC50 of 5 mg/ml at 48 h towards Artemia salina and slight genotoxicity when tested against human lymphocytes.