The Sciences

Glowing Algae off Mumbai's Shores Could Be Due to Climate Change

Algae can paralyse fish, clog their gills and absorb enough oxygen to suffocate them.

After a year’s research, a team of Indian and American scientists has found that ‘glow-in-the-dark’ algae in the waters off Mumbai’s shores could be born of global warming, and may not be the product of pollution from Indian cities, as was thought earlier.

Noctiluca is a parasite and a type of bioluminescent algae. It is often found in the northern Arabian Sea, and has been nicknamed ‘sea tinkle’ and ‘sea sparkle’ thanks to its ability to glow by emitting bluish light at night. When these algae gather, the patch of water appears to glow blue. However, these patches compete with fish for diatoms, an important kind of planktonic organisms.

Noctiluca also excretes ammonia into the water. Excess ammonia accumulates in the fish and alters their metabolism or changes their body’s acidity. In extreme quantities, fish may experience convulsions, coma and death.

Algae can paralyse fish, clog their gills and absorb enough oxygen to suffocate them. Whales, turtles, dolphins and manatees have died poisoned by algal toxins in the Atlantic and Pacific.

Although no link has been elucidated between low oxygen levels in the water and the growth of these algae, global warming has also been slowing the upward transport of nutrients like silicates from the ocean floor. While this is bad news for diatoms, it’s good for Noctiluca patches.

Diatoms growing in surface water need both sunlight and silicates to build their skeletons. When there is a shortage of these compounds, diatoms’ numbers dwindle. On the other hand, Noctiluca remains unaffected by these changes and will also prey on the remaining diatoms.

Additionally, warmer waters don’t mix well, and allow smaller organisms like algae to float faster to the surface. These conditions allow Noctiluca to survive better and, at the surface, absorb sunlight and warm the water further.

S.C. Shenoi, director of the Indian National Centre for Ocean Information Services (INCOIS), an ocean sciences research institute in Hyderabad, told Livemint, “Less dense water comes to the surface because of the warming of oceans, encouraging these intense blooms, which has an adverse impact on fisheries.

“Currently, the western coast, Persian Gulf, and Oman are largely affected, but if it keeps on increasing, it will have drastic effects on fisheries along the Indian coast.”

The study’s authors echoed this, noting in their that “the waters in the study area were observed to have sufficient oxygen, clearly opposing any linkage between low oxygen and Noctiluca growth. Intensifying global-warming conditions, thus, may be expected to disrupt the fish-food chain and cause a decline of fisheries in the region.”

According to Times of India, INCOIS – which deals with changes in the ocean, monsoons, fisheries and tsunamis – has been conducting conducting studies about fish mortality in the Arabian sea.

INCOIS is currently setting up a marine observation system called MOSAIC. It is a network of automated buoys to monitor the quality of water along India’s coast.

The algae’s glowing prowess is enabled by an enzyme, luciferase, and a molecule called luciferin, produced by photosynthesis. When algae are disturbed, a series of chemical processes inside their cells cause their pH levels to drop. This activates the luciferase, which binds to the luciferin and transfers energy through oxidation. When the luciferin releases the energy, it’s in the form of blue light.