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Indian Journal of Ecology
Year : 2022, Volume : 49, Issue : 3
First page : ( 894) Last page : ( 899)
Print ISSN : 0304-5250.
Article DOI : 10.55362/IJE/2022/3612

Recurrence of dinoflagellates, Noctiluca scintillans bloom and impact on marine faunal communities of mandapam coastal waters in gulf of mannar, southeast coast of India

Sadhukhan Koushik*, Reddiar Shanmugaraj Thimmu, Mallavarapu Ramana Murthy Venkata

National Centre for Coastal Research, Ministry of Earth Sciences, Mandapam Field Research Centre Mandapam Camp- 623 519, India

National Centre for Coastal Research, Ministry of Earth Sciences, Pallikaranai, Chennai- 600 100, India

*E-mail: sadhukhan.1985@gmail.com

Online Published on 19 September, 2022.

Abstract

Massive blooms of Noctiluca scintillans reoccurred at several regions of Mandapam coastal waters between 22nd September and 30th September, 2020. Bloom lasted for nearly one month, causing mortality of fishes and other marine organisms by facilitating hypoxia condition in the water column. Fifteen locations in four areas, namely Hare Island, Vedhalai seashore, Seniappadarga, Pudhumadam and Manoli Island have been surveyed thoroughly to understand the bloom's intensity and its impact on marine biota. Mass mortality of marine organisms was reported during this survey including fishes, octopus, sea cucumbers, sea anemones, crabs and sea shells due to the bloom incidence. A total of 371 numbers of marine organisms were dead during the bloom. The cell density of N. scinitillans bloom was 14.7 x 105 cells l−1 in core dense area, 8.6 x 105cells l−1 in semi-dense area, 0.47 x 105cells l−1 in less dense areas, and 1440 cells x l−1cells in clear water. Physicochemical parameters measured in the bloom region were sea surface temperature 32.3°C, Salinity 35.78ppt, dissolved oxygen 4.61 mg/l and pH 7.11 ± 1.02, Phosphate 2.831µM, Nitrate 2.407 µM and ammonia 31.324µM. The high level of phosphate triggers the growth of algal bloom which results in sudden drop of dissolved oxygen and triggers the death of fishes and marine invertebrates in the bloom regions. There is no adverse impact found on scleractinian corals. Post bloom investigations are underway to report the further adverse effect on the ecosystem's marine resources or resilience to recover from the sudden natural damage.

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Keywords

Algal bloom, Noctiluca scintillans, Cell density, Nutrient, Sea surface temperature.

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