Marine fisheries and biodiversity in the Gulf of Mannar, Tamil Nadu, were severely impacted by the blooms of dinoflagellate Noctiluca scintillans, on 10th October 2021. The bloom affected the marine biodiversity in a 15 km2 area between Keelarai to Mudal in the Gulf of Mannar, Tamil Nadu, India. Post bloom observations showed mass mortality of a variety of finfish, ornamental fish, bivalves, shellfish, sea anemones, sea slugs, sea cucumbers, sea horses, polychaete worms, and seaweed that washed ashore. Two damselfish species Dascyllus reticulatus and D. trimaculatus were deleteriously affected. The intense N. scintillans bloom killed 0.83 tons of damselfish, equivalent to approximately 9 million fish, and 1.67 tons of commercially important fish valued at US$ 11.5 M.

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