Bioluminescence lights up beaches along Chennai’s coast

At around 3:30 a.m. last Tuesday, surfer Saravanan. B, who runs Saro Surf School, was just making his way into the sea when he spotted bioluminescence; the waves off Kovalam beach lit up in electric blue. Since word of this rather unusual sighting made the rounds, many inquisitive onlookers have been gathering along the shore from dusk till dawn to catch a fleeting glimpse of this phenomenon first hand.

“I spotted it in 2024 too, and it was such a spectacular sight,” said Mr. Saravanan. “I have witnessed it multiple times this month. But we can’t plan an outing around it because it is unpredictable. Last night, we went to see it, but it did not make an appearance,” he added.

Another resident of Chennai, Sujith Sivakumar, recounted his experience of a bioluminescence sighting at Thiruvanmiyur beach at around 4:50 a.m. on Thursday. Describing it as a magical experience, he said, “Seeing the waves glow with an ethereal blue light against the dark shoreline felt completely surreal like something straight out of a fantasy film,” he said.

Narayanan, a fishing community leader, also said that many fishermen have spotted this phenomenon in the waters off Kovalam this season.

Explaining the ecology of blue-lit coastline, ecologist Ranjit Daniels of Care Earth Trust noted that bioluminescence is a characteristic of many marine organisms inhabiting the deep sea, where they use it to communicate with each other. This is found in marine organisms like jellyfish, squids, deep-sea shrimps, and dinoflagellates, to name just a few. “Bioluminescence is a very well-known phenomenon among organisms that live in the deeper sea and use this ability for various survival purposes,” he said.

According to a case study by Mishra et al. of the National Centre for Coastal Research, following a spell of heavy rain in 2019, there was an unusual occurrence of heterotrophic bioluminescent dinoflagellates along the Chennai coast. Regarding that year’s sighting, the study noted that environmental factors such as high atmospheric temperatures change the sea surface temperature and increase the availability of dissolved nutrients. These conditions promote the growth of Thalassiosira (a type of microscopic algae), which provides favourable conditions for the rapid growth of Noctiluca scintillans, a plankton responsible for the blue bioluminescence sometimes seen in seawater.