Lakshadweep sees drastic coral bleaching from marine heatwaves

Researchers at the ICAR-Central Marine Fisheries Research Institute (CMFRI) have recorded widespread bleaching of the coral reefs in the Lakshadweep Sea, owing to marine heatwaves.

It was revealed in a survey undertaken across various Lakshadweep Islands that a considerable percentage of the hard coral species have undergone severe bleaching, primarily due to a prolonged period of marine heatwaves since late October 2023.

Marine heatwaves are rare 'extreme weather' events that involve prolonged periods of abnormally high ocean temperatures. To qualify, the temperatures must typically exceed the 90th percentile of typical regional ocean temperatures based on historical data.

In Lakshadweep, the degree heating week (DHW) indicator, which measures accumulated heat stress, has surged above 4 degrees Celsius-weeks.

According to the National Oceanic and Atmospheric Administration (NOAA), this level of DHW poses a substantial risk of coral bleaching, threatening the region's diverse marine ecosystems.

Dr K.R. Sreenath, senior scientist at CMFRI, said such heat stress represents a severe threat to coral health, leading to extensive bleaching where the corals lose the symbiotic algae (zooxanthellae), compromising their chances of survival as it deprives them of essential nutrients.

“If the DHW continues to rise, reaching beyond 12 degrees Celsius-weeks, it could precipitate an unprecedented biodiversity crisis due to multi-species mortality,” said Dr Sreenath.

According to Dr Shelton Padua, senior scientist at CMFRI, the primary causes of these marine heatwaves is excessive atmospheric transfer of heat, coupled with shifts in ocean currents, leading to unusually high water temperatures.

“Since 27 October 2023, the Lakshadweep Sea, spanning from 80.0 N to 12.0 N latitude and 71.0 E to 75.0 E longitude, has been experiencing these conditions, with temperatures consistently registering rises greater than 1 degree Celsius above the norm,” said Dr Padua.

The health of marine ecosystems is integral to the livelihoods of coastal communities, influencing tourism and fisheries sectors too. Therefore, Dr Sreenath said, the ongoing marine heatwaves are likely to cause significant economic losses as well, in addition to disrupting vital aspects of the ecosystem here.

“Death and disintegration of coral reefs can threaten the coastal communities, leaving them (more) vulnerable to the impacts of sea-level aggressions,” Dr Sreenath added.

The CMFRI has been actively undertaking studies to better understand ecological changes affecting coral reefs, in addition to a comprehensive national project that hopes to establish the resilience potential of various coral reefs in India.