Environmental impact assessment of algal bloom Noctiluca scintillans in the Mandapam group of Islands, Gulf of Mannar Biosphere Reserve, Southeast coast of India.

Abstract

The present investigation accounts for the environmental impact assessment of an intense algal bloom caused by the dinoflagellate Noctilucas scintillans. The bloom was first observed on the 10th of September 2019, in the vicinity of the Mandapam group of Islands, spreading from Rameswaram Coast in the North (9° 14' 15″ N, 79° 9' 46″ E) to Hare Island in the South (9° 14' 51″ N, 79° 5' 48″ E). The coastal waters in and around the Mandapam region appeared dark green, and the microscopic examination of the water sample revealed the presence of N. scintillans in large numbers. N. scintillans is a bioluminescent organism; it is inflated and sub-spherical in shape, and the size of the organisms ranged from 350 to 1300 microns. During the intense periods of the bloom, the average density of N. scintillans was recorded with 226.5 × 103 cells/l, and the dissolved oxygen content was very low and the ammonia content was extremely high in certain sites (avg. 4.3635µm/l). Intensive bloom may lead to a loss of biodiversity in the affected areas of the region. Subsequent investigations indicated that the resilience of the ecosystem in response to natural adversity.