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Explained: What explains the ‘blue tide’ at Mumbai beaches?

Bioluminescence or light-emitting tide made an appearance on Tuesday night on Juhu beach in Mumbai and Devgad, Velas and Murud along the state's coastline.

Written by Sanjana Bhalerao , Edited by Explained Desk | Mumbai | Updated: December 5, 2020 3:44:39 pm
A beach in Chennai witnesses bioluminescence or blue sea sparkle. Bioluminescence is the property of a living organism to produce and emit light. (ANI Photo/File)

Over the last four days, visitors to beaches in Maharashtra have witnessed the spectacle of a fluorescent bluish glow when the waves hit the shoreline. Bioluminescence or light-emitting tide made an appearance on Tuesday night on Juhu beach in Mumbai and Devgad, Velas and Murud along the state’s coastline.

Why did the waves appear blue?

The phenomenon is called ‘blue tide’, and appears when luminescent marine life make the sea appear a deep shade of blue. The spectacle occurs when phytoplankton (microscopic marine plants), commonly known as dinoflagellates, produce light through chemical reactions in proteins, said researchers. Waves disturb these unicellular microorganisms and make them release blue light.

What is Bioluminescence?

Bioluminescence is the property of a living organism to produce and emit light. Animals, plants, fungi and bacteria show bioluminescence. A remarkable diversity of marine animals and microbes are able to produce their own light. It is found in many marine organisms such as bacteria, algae, jellyfish, worms, crustaceans, sea stars, fish and sharks. Luminescence is generally higher in deep-living and planktonic organisms than in shallow species.

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Why do they glow?

It is an antipredatory response. Bioluminescence is assumed to startle predators, causing them to hesitate, in a form of predator intimidation. Another explanation is that bioluminescence helps these organisms gather together and make colonies. 📣 Express Explained is now on Telegram

Are bioluminescent waves common in India?

Bioluminescence has been an annual occurrence along the west coast since 2016 during the months of November and December. The sight was observed at Juhu on Wednesday night, and at Devgad and Velas beaches in Ratnagiri. Recently, the ‘blue tide’ was witnessed along Dakshina Kannada-Udupi coast.

While bioluminescence is not common in India, there are several tourist places across the world which are famous for the phenomenon. The Blue Grotto in Malta is one of nine caves near the island of Filfa that produces a phosphorescent glow. Similar to the Blue Grotto is Bioluminescent Bay in Puerto Rico, San Diego in California, Navarre Beach in Florida, and Toyama Bay in Japan.

Is the blue tide harmful?

While smaller blooms may be harmless, slow-moving larger blooms may have an impact on deep-sea fishing. According to marine experts, the phenomenon is an indicator of climate change. Factors such as the pattern of the wind and the temperature of the ocean also determine the occurrence of bioluminescent waves.

Gurudas Nulkar, trustee of Ecology Society and professor at Symbiosis International University said, “It is a spectacle but in reality, it is an ecological indicator of degraded water quality. The phytoplankton shows up where seawater has low dissolved oxygen and high presence of Nitrogen.”

Experts have said the bioluminescence could have been caused by heavy rain, fertilizers run off, discharge of sewage into the ocean.

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