SINGAPORE – The teenager had just switched off his torch and was standing in the darkness in Changi Beach when he saw glimmers of blue light bursting from the water near the shoreline.
“This is the first time I’ve seen the ocean glow like that,” said 18-year-old Kuppusamy Velmurugan Aravindh about what he witnessed on Oct 27.
The student, who attends the NUS High School of Mathematics and Science, was there that day guiding three of his friends along the intertidal zone at low tide, at about 7.30pm. Since March, Aravindh has led almost monthly intertidal walks to help his friends appreciate marine wildlife. His interest was sparked by a school trip to Pulau Hantu in 2021.
Aravindh went back with his friends the next day, as well as the day after that, and noted that the flashing lights had intensified.
But the blue sparkles he saw were not due to bioluminescent algal blooms, which lit up the shores of Pasir Ris and Changi in March; instead, the light was emitted by tiny marine crustaceans known as ostracods, or sea fireflies.
“Unlike the dinoflagellates in March, these glowing dots were spaced out around us, like stars in the black sea. They left shimmering trails behind them,” said Ms Kong Man Jing, co-founder of science and nature channel Just Keep Thinking.
A video about the glow in Changi Beach was uploaded on Just Keep Thinking’s Facebook, YouTube and Instagram pages, where Ms Kong linked the spectacle to the ostracods.
The 28-year-old also witnessed the phenomenon at 9pm on Oct 29, while guiding a mixed group of adults and children.
“We spent about 20 minutes trying to see where and how big the creatures were, and we realised that they were the size of a grain of sand. It was quite mesmerising,” she said.
To appreciate the spectacle of these sea fireflies, people should avoid getting in the water and stomping on them – keeping a respectful distance provides a clearer view, added Ms Kong.
Dr Jose Christopher Mendoza, senior research fellow and curator of crustaceans at the National University of Singapore’s Lee Kong Chian Natural History Museum, said that although bioluminescent ostracods in South-east Asia have been observed for quite some time, this may be the first documented instance of the crustaceans’ glow in Singapore waters.
He added that he has not encountered any accounts of such light displays occurring in Singapore in his research.
Around the world, from Japan to the Caribbean, marine ostracods have dazzled people with their natural light shows.
Dr Mendoza said: “Bioluminescence is usually produced when the animal is disturbed, say by potential predators, and so the blue flashes are supposed to confuse or scare potential predators.
“Some research has shown that sea fireflies use bioluminescence for communication, specifically for attracting mates, something similar to what fireflies do.”
When needed, marine ostracods will release luciferin, a protein, and luciferase, an enzyme, with some bodily fluids – usually mucus – creating a luminous blue trail of chemicals.
Dr Mendoza said: “The light is produced when luciferin and luciferase combine in the presence of oxygen, and luciferin enters an excited state, which causes it to release photons.
“This can be seen as a flash of blue light.”
In Japan, dried ostracods are popular because they still sparkle when rehydrated, according to the journal Science.
While some samples of ostracods were collected in Singapore’s last mega-marine survey that took place in 2010 and 2015, they are poorly known because of their relatively small size, said Dr Mendoza.
“We still don’t know a lot about the local species, their identities, their ecology and their behaviour.
“Sometimes, spectacular displays, such as the one in the video (filmed by Just Keep Thinking), can be observed by luck. When and why these things happen, we’re not sure,” he added.