Note on the fish species affected by the sea sparkle bloom in the coastal waters of the Gulf of Mannar

Rajkumar, M and Thirumalaiselvan, S and Remya, L (2024) Note on the fish species affected by the sea sparkle bloom in the coastal waters of the Gulf of Mannar. Marine Fisheries Information Service No.260. pp. 31-32. ISSN 0254-380X

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Abstract

A 6-kilometer stretch of coastal waters between Periyapatinam (9.250915 N, 78.909109 E) and Indira Nagar (9.265104 N, 78.923969 E) in the Gulf of Mannar witnessed a Noctiluca bloom from August 28th to September 2nd, 2022. The bloom of Noctiluca scintillans (Macartney), a bioluminescent dinoflagellate with a size range of 0.6 to 1.15mm that emerged on September 2nd, 2022, turned coastal waters green, affecting small pelagic fish and reef-associated fish, and emitting a foul odour. We identified and quantified the species diversity of fish that perished during the bloom period. From an estimated 2.5 tonnes of fish washed up on the beach, 50% of the fish were from the family Clupeidae, followed by Gerridae and Leiognathidae. These stranded fish were collected by local fishermen. The 53 stranded fish species include 46 teleosts, 5 crabs, and one sea anemone and annelid species each. Since 2019, Noctiluca blooms have been a regular occurrence in the Gulf of Mannar during the brief period between the southwest and northeast monsoons. However, in 2022, the Noctiluca bloom started as early as the middle of August, and continued till October, during which we maintained bloom monitoring. The primary causes of fish death in Periyapatinam and Indira Nagar coastal waters were low dissolved oxygen and an increase in ammonia concentrations. The observations during the close monitoring of the algal bloom along the coast provided information of the species with size range, that died due to the algal bloom.

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