Marine heatwaves: Intense coral bleaching recorded in Lakshadweep

Kochi

In an alarming situation, the researchers of the ICAR-Central Marine Fisheries Research Institute (CMFRI) have recorded a widespread bleaching event impacting the coral reefs in the Lakshadweep Sea owing to marine heatwaves.  Survey results from various Lakshadweep Islands revealed that a considerable percentage of the hard coral species have undergone severe bleaching, primarily due to a prolonged period of marine heat waves affecting the region since late October 2023.

Background on Marine Heatwaves

Marine heatwaves are rare extreme weather events that involve prolonged periods of abnormally high ocean temperatures. These temperatures often 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 °C-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.

Impacts on Coral Reefs

“Such heat stress levels signify a severe threat to coral health, leading to extensive bleaching where corals lose the symbiotic algae (zooxanthellae), compromising their survival by depriving them of essential nutrients. If the DHW continues to rise, reaching beyond 12 °C-weeks, it could precipitate an unprecedented biodiversity crisis due to multispecies mortality”, said Dr K R Sreenath, Senior Scientist of CMFRI. 

Cause and Continuation of Heatwaves

Dr Shelton Padua, Senior Scientist at CMFRI identifies the primary causes of these marine heatwaves as excessive heat atmospheric transfer coupled with shifts in ocean currents, leading to unusually high water temperatures. Since October 27, 2023, the Lakshadweep Sea, spanning from 80.0 to 12.0 N latitude and 71.0 to 75.0 E longitude, has been experiencing these conditions, with temperatures consistently registering rises greater than 1°C above the norm.

Socio-Economic Consequences

Viewing that the health of marine ecosystems is integral to the livelihoods of coastal communities, influencing tourism and fisheries sectors, Dr Sreenath said that the ongoing marine heatwaves are likely to cause significant economic losses by disrupting their vital ecosystem services. Furthermore, death and disintegration of coral reefs can threaten the coastal communities, leaving them vulnerable to the impacts of sea level aggressions.

Other Marine Ecosystems Affected

“The ongoing heat waves also threaten other critical marine habitats, including seagrass meadows. Similar to corals, seagrass meadows are experiencing detrimental impacts due to the heatwaves, such as impaired photosynthesis, reduced growth, and hindered reproductive functions. The degradation of these ecosystems can lead to the collapse of local marine food webs, affecting a wide range of marine species, from fish communities to marine mammals like dugongs and dolphins”, Dr K R Sreenath said.

Research and Development Initiatives by CMFRI

CMFRI has been actively undertaking studies to better understand ecological changes affecting coral reefs. CMFRI has initiated a comprehensive national project aimed at investigating the resilience potential of various coral reefs in India. By integrating advanced climatic modelling, deep-learning, and ecological research, CMFRI aims to enhance survey efficiency and develop resilience-based management actions ensuring the long-term sustainability of coral reef ecosystems.