• Ashinsa de Silva Wijeyeratne

Stars in the Sand

The pristine beaches of the Maldives shimmer at night with the bioluminescence of microorganisms.

While on holiday in the Maldives on the island of Embudu, I met a lovely lady who told me to visit one of the islands’ several beaches at night to see a phenomenon she described as being “like the stars in the sky had fallen onto the sand”. I’d only read about this in passing, but my curiosity and excitement was piqued. I headed to the beach after dinner and walked down to where the waves were gently lapping against the shore. And then I saw it. With each lapping wave, the edge of the water shimmered an otherworldly blue. It was gone in seconds but reappeared as the waves broke. I dug my feet into the sand near the water and that too yielded smatterings of glowing blue light. It really did look like the stars had fallen onto the beach.These ‘stars’ however, were very much alive and their glow was a result of a chemical reaction – bioluminescence.

Stars in the sand. Used with permission from joreymaldives.

Bioluminescence is the production of light by a living organism. Bioluminescent micro-sea creatures include phytoplankton -diatoms and dinoflagellates- and ostracod crustaceans. These minute animals produce light for various reasons, such as to ward off predators and attract mates. Light is produced by an enzymatic reaction, using a molecule known as Luciferin and an enzyme that breaks it up, Luciferase. The exact mechanism differs with species, but the final outcome is the production of light for a brief period. Mechanical stress can set off the reaction as well, which is why the glowing blue appears only when the waves break or when the sand around is dug. Several macroscopic animals show bioluminescence too, among which fireflies are the best known, but also include jellyfish, squid, and glow worms.

Dinoflagellates are protists that are largely present in marine environments. Some are photosynthetic, while others are parasites. They can cause ‘algal blooms’ by multiplying rapidly and in large numbers. These blooms can result in ‘red tides’ as the water may appear pink/red in colour. Dinoflagellates produce a neurotoxin which can affect the marine life in the area and even humans, if they consume shellfish or fish that have ingested the toxin.

Diatoms are unicellular microalgae, which can form various shapes due to the presence of a cell wall made of silica. Known as a ‘frustule’, this unique feature of diatoms is used by humans as ‘diatomaceous earth’. They make quite a beautiful picture under a microscope!

The colourful varieties of diatoms as seen through a microscope.(CC-BY-SA 3.0)

Bioluminescent microorganisms can be found in the waters of many regions, both tropical and temperate. So, the next time you think you see a glow in the ocean, don’t worry, it’s nothing supernatural or extra-terrestrial! Just one of nature’s many wonderful phenomena.

The glowing blue waters of the Maldives. Used with permission from yoosuf_suhail.

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