It is nearly August, and it is, perhaps, time for heavy rain and blooms along the beaches in Chennai.
Adequate nutrients brought by substantial rain and a high abundance of the plankton, called diatom Thalassiosira sp. triggered the (bioluminescent) bloom of Noctiluca scintillans, says a study done by the National Centre for Coastal Research (NCCR).
The plankton is available in the ocean and due to nutrition available, it will multiply and becomes the bloom. Low wind speed, lowering of atmospheric temperature, high rain and low sea surface temperature are cited as probable environmental cues, the report said.
Local hydrodynamics and the diverging currents governed the presence and dispersion of the sudden outbreak of the bioluminescent dinoflagellate Noctiluca scintillans bloom in the region.
The paper, which was written by Pravakar Mishra, Mehmuda Begum, Anitha Gera and others and published recently in the scietific journal Oceanologia, focused on the occurrence of bloom along a 16-km stretch following a spell of heavy rain in August 2019.
During the period, when the team took physical samples from the beaches, including Marina, Elliots, Panaiyurkuppam and Kovalam, the wind speed was low at 5 m/sec, temperature fell, high rainfall was recorded one day, and sea surface temperature was low.
The density of Noctiluca scintillans varied from 1,000 cells/litre to 19,000 cells/litre, with a distinguished distribution pattern. An abundance of scintillans was recorded at Panaiyurkuppam and Kovalam with 19,000 cells/litre and 18,000 cells/litre respectively.
The paper explained that once the bloom reduces, there is an increase in bacterial population associated with the phyto-plankton bloom. The lowest count was recorded on the Panaiyurkuppam beach and the maximum on Elliot’s Beach. Total coliform too was recorded in the waves.
Bioluminescence was observed owing to turbulence and intense wave breaking in the surf zone, stimulating bioluminescence in Noctiluca scintillans cells. Within two days after the appearance of bioluminescence, the blooming cells slowly degenerated and moved away by the current, and finally declined.
