In the past few years, bright blue, glow-in-the-dark waves have lapped at Mumbai beaches at night, caused by a bloom in the bioluminescent plankton Noctiluca scintillans.
Despite the striking visuals, N. scintillans is harmful to fish because it competes with them for plankton called diatoms and releases ammonia, which has been associated with mass fish die-offs, The Hindu reported.
Previous research had suggested the bioluminescence was due to agricultural and industrial runoff from the coasts, but the new study by the Indian National Center for Ocean Information Services (INCOIS) and the National Oceanic and Atmospheric Administration (NOAA) found that the warming of the oceans, which leads to greater temperature differences between ocean layers, was the more likely culprit.
If the phenomenon continues, it could have a serious impact on the Indian fishing industry.
“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. That could be alarming,” INCOIS Director Dr. S.C. Shenoi told Mint.
As a result of the study, INCOIS announced plans to set up a program called Marine Observation System along Indian Coast (MOSAIC) to keep track of the health of the subcontinent’s coastal waters.
The reason the scientists ruled out pollution as a cause was that there was plenty of oxygen towards the ocean’s surface, where the plankton bloom is occurring. The previous study had blamed it on oxygen minimum zones, but the new study found those zones were too deep to have an impact.
Instead, the increasing difference in the temperatures of ocean layers means that nutrients like silicate travel upwards more slowly. Diatoms need both silicate and sunlight to thrive, so this discourages their growth and increases the N. scintillans that preys on them.
“The present findings show no evidence that cultural eutrophication has contributed to the decadal scale shifts in plankton (algae) composition in the north- eastern Arabian Sea. Instead, the lessons that are learned here may help to forecast the effects that climate change may have in other productive oceanic ecosystems,” stated the research paper, according to Mint.
In addition to Mumbai’s Juhu Beach, the glowing waves have also been observed along the coasts of China and Hong Kong within past three years, The Washington Post reported.