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Hindustan Times
4 days ago
- Science
- Hindustan Times
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.
Asahi Shimbun
10-05-2025
- Science
- Asahi Shimbun
Corals bounce back quicker on artificial structures
Corals growing on artificial breakwaters (Provided by the Port and Airport Research Institute) Artificial structures like concrete breakwaters to protect shorelines seem to offer a quicker fix than natural reefs for corals devastated by bleaching events, say Japanese researchers studying how climate change affects the sea floor. Bleaching refers to the whitening of corals due to rising seawater temperatures. Severe or frequent bleaching events can kill the underwater ecosystems. It turns out that corals tend to recover more quickly on artificial structures. Typically when scientists study the phenomenon, they spend up to 10 years collecting field data. For the latest study involving the Port and Airport Research Institute (PARI) and other entities, researchers in Okinawa Prefecture relied on 29 years of field data along three breakwaters, as well as in surrounding natural reefs in Naha Port. The data in question covered the period from fiscal 1989 through fiscal 2018. A large-scale bleaching event occurred in the surrounding waters in 1998. Corals in natural reefs were found to have covered only 5.2 percent of the seabed in 2001, and 5.6 percent in 2004. But when breakwaters were examined, corals were found to have recovered more rapidly, from 8.8 percent in 2001 to 25.4 percent in 2004. Moreover, the cover rate remained high in subsequent years. DIFFERENT CORAL COMPOSITIONS The corals did not have the same taxonomic composition on the breakwaters that they had in the natural reefs. Corals of the genus Acropora, which are more likely to inhabit sites exposed to pounding waves, accounted for a large part of the rapid post-bleaching recovery on the wave-dissipating blocks, whereas relatively slow-growing corals, including those of the genus Porites and the family Faviidae varieties, increased gradually in proportion in the natural reefs. The researchers also found that coral recovery was accelerated by grooves on the surface of the artificial structures. They discovered that corals were more abundant in shallow waters where the sunlight on moderately sloped substrate was strong. When part of a breakwater was modified into zones that met those conditions, the area covered by coral increased by about 40 percent. PRECIOUS LONG-TERM DATA The study relied on data gathered by the Okinawa General Bureau, a government body that supervises Okinawa's promotion and development that discovered coral-covered breakwaters in the 1980s and subsequently began making observations in surrounding areas. Past studies around the world have looked at using artificial structures as substrate for corals, but the research periods never lasted longer than 10 years, and none covered such a long span as the latest one, said Toko Tanaya, a PARI senior researcher who was on the team. But why coral regeneration occurred faster on the artificial structures is a subject for future studies, Tanaya said. However, she said it seems likely that artificial breakwaters, given their sturdiness and location in areas exposed to pounding waves, attract fast-growing coral varieties, such as species of the genus Acropora. 'Of course, the best thing would be to make sure that natural coral reefs survive,' seeing as different ecosystems can result from restoration in natural reefs and on artificial structures, Tanaya said. 'Climate change has made bleaching so frequent in recent years that corals no longer have enough time to recover before the next bleaching event occurs,' she added. INFRASTRUCTURE NOT INTENDED FOR CORALS When bleaching occurs, algae and other creatures may attach themselves to the dead coral with the result that the limestone skeletons collapse and pile up like rubble. When that happens, the skeletons are too wobbly and unstable for new larvae to stick to and survive, Tanaya said. However, breakwaters and similar coastal erosion defenses are not put in place for the sake of corals, she noted. Still, a few modest improvements made while they are being built or repaired 'could help ensure the availability of shallow-depth zones that are suitable for the growth of corals,' Tanaya added. The research results were published online in the journal Scientific Reports (
