4 days ago
Lakshadweep reefs resilient to climate heating, says two-decade study
Panaji: India's major coral reefs in the Lakshadweep Islands displayed strong resilience against climate heating, while those in the Gulf of Kachchh were the most susceptible, according to a research study that examined 23 years of bleaching events on Indian coral reefs since 1998 to assess their impact.
Bleaching events refers to stress response in corals where they expel the symbiotic algae (zooxanthellae) that live within their tissues, causing the corals to turn white.
The research study was published in Estuarine, Coastal and Shelf Science in February after oceanographers examined major bleaching events in 1998, 2010, and 2016 in the Gulf of Kachchh, the Gulf of Mannar Biosphere Reserve, the Lakshadweep Islands, and the Andaman and Nicobar Islands to examine their impact on coral reefs.
The research — a collaborative effort between Thangadurai Thinesh, an assistant professor in the department of Marine Science and Fisheries at Sultan Qaboos University in Oman, and Kalyan De from the National Institute of Oceanography — examined 23 years of bleaching episodes on Indian coral reefs (including four major reefs and other patch reefs) to understand the geographical footprint of bleaching patterns, species-specific susceptibility, and their overall impact.
The study has revealed that among India's major coral reefs, those located at the Lakshadweep Islands displayed the most resilience to heating episodes, described in terms of degree heating weeks (DHWs), while those in the Gulf of Kachchh were the most susceptible.
Lakshadweep 'displayed a perfect negative correlation' with heating episodes, while the Gulf of Kachchh had the strongest positive correlation, meaning that bleaching was strongly tied to DHWs. The reason, according to the scientists, was the abundance of genera of massive corals known as Porites, that have been 'found to exhibit higher resistance and recovery potential following thermal stress.'
'In contrast, reefs in the Gulf of Mannar and the Andaman Islands—dominated by more sensitive branching genera like Acropora, Montipora, and Pocillopora—experienced higher bleaching rates and lower recovery,' Thangadurai, lead author of the paper, said.
'However, this resilience has limits. When heat stress becomes more intense and prolonged, differences in susceptibility begin to disappear, and even the more resilient corals can bleach and die,' he added.
The Gulf of Mannar had the highest bleaching in 1998, followed by 2016, and the lowest in 2010. The Andaman Islands peaked in 2010, followed by 1998, and had no bleaching percentage reported in 2016 despite DHWs of 7.21–9.5. Lakshadweep recorded the highest bleaching in 1998, followed by 2010, and the lowest in 2016. The Gulf of Kachchh peaked in 2010, followed by 1998 and then 2016. The correlation between DHWs and coral bleaching percentages varied across reef sites.
Apart from the four major coral reef regions, India has a few patch reefs --- three patch reefs at Palk Bay, the Malvan Marine Sanctuary (Maharashtra), and the St. George Islands (Grande and Pequeno) in Goa, as well as a few patches at various locations such as Ratnagiri, Redi (Maharashtra), Netrani (Karnataka), Quilon on the Kerala coast to Enayem in Tamil Nadu, Parangipettai (Porto Novo), south of Cuddalore, and Pondicherry.
India's estimated coral reef area is around 2,383.87 km². These coral reefs harbour 585 species belonging to 108 genera and 23 families. All three major bleaching events (1998, 2010, and 2016) affected all four major reefs, causing mortality.
The researchers believe that 'India urgently needs a coordinated national monitoring program to make informed conservation decisions, prioritising consistency and long-term observation,' for which an understanding of which coral species can withstand rising temperatures is crucial.
'Coral transplantation is a valuable conservation effort already underway at several sites in India, demonstrating a proactive approach to reef restoration. These initiatives show promise in helping damaged ecosystems recover. However, without a clear understanding of which coral species can withstand rising temperatures, there's a risk that some of these efforts may fall short. Transplanting heat-sensitive corals into areas prone to thermal stress could lead to poor survival rates. To make restoration more effective, it's essential first to identify thermally resilient species and match them to suitable environments,' Thangadurai said.
The researchers, however, cautioned that 'one-time surveys often misrepresent bleaching impacts, overestimating stress in resilient species and missing early mortality in sensitive ones,' and called for 'repeated, standardised surveys' to 'accurately capture which corals are truly vulnerable or resilient over time.'
'These actions will enable more targeted, effective conservation. And this work isn't just about saving corals—it's about protecting the livelihoods, food security, and coastal defences that millions of people rely on,' he added.
