Lakshadweep's coral cover halved in 24 yrs
The paper concluded that the fate of corals in Lakshadweep will be determined by the return time of bleaching events, underscoring that urgent climate action is critical to secure the ecological integrity of tropical reefs. The scientists leading the study, including Rohan Arthur and Mayukh Dey from the Oceans and Coasts Programme of Nature Conservation Foundation concluded that 'the one thing reefs need to recover is time'.
'Without a pause in the frequency of marine heatwaves, whatever resilience tropical reefs have is likely to be short lived. Our results show that fewer corals die simply because less is available to die in later years,' they added.
'In the long run, we must call the crisis by its name and acknowledge that the integrity of tropical reefs, like the rest of global biodiversity, cannot sustain the seemingly impervious logic of the prevailing economic order. Without scale-appropriate radical policies, laws, and actions to address these ultimate causes, anything we do locally for reefs will be symptomatic and palliative fixes,' the scientists said.
Lakshadweep Archipelago has 12 coral atolls in the northern Indian Ocean. The archipelago is among the most densely populated atoll systems globally with 10 populated islands, with more than 2000 people/sq km. Lakshadweep has experienced three marine heatwaves associated with the El Niño phase of the ENSO phenomena in 1998 (5.3 Degree Heating Weeks, DHW), 2010 (6.7 DHW) and 2016 (5.2 DHW), with 2010 being the most severe of the three.
Hindustan Times, in a series on Lakshadweep published last year reported how the islands experienced a severe bleaching event in 2024. The heat stress in Lakshadweep (Laccadive Sea) and in Southeast India was record-setting in 2024 according to Derek P Manzello, Coordinator, NOAA Coral Reef Watch.
The metric used to gauge heat stress on corals is called Degree Heating Weeks (DHW). DHW shows how much heat stress has accumulated in an area over the past 3 months. In 2024, Lakshadweep reached 9.2 DHWs, whereas SE India reached 9 DHWs. The prior record for Lakshadweep was 6.7 DHW in 2010, and it was 6.9 DHW for SE India in 2016, said Manzello.
Since 1998, researchers from the Nature Conservation Foundation have been tracking reef conditions at three atolls across the Lakshadweep Archipelago , Agatti, Kadmat and Kavaratti , to understand how reefs respond to climate change. This monitoring programme has monitored reefs as they declined and recovered from three major El Niño Southern Oscillation (ENSO) events — in 1998, 2010 and 2016. The data was analysed to explore if changes in the composition of coral could be explained by the number of heatwaves experienced and by more local factors, such as seasonally strong wave action and depth at which corals are found.
The team also found that these results challenge the simplistic narrative that all coral reefs respond in a similar fashion to climate change, and are universally doomed. Even within a small archipelago like Lakshadweep, there is a large variability in responses -- sometimes in reefs only a few kilometres apart.
'The Lakshadweep reefs have been home to me since I first dived here as a young researcher. To see these diverse ecosystems decline before my eyes is soul-destroying. Our findings are a bittersweet offering. On the one hand, it shows me that the reef is more complex and more resilient in its responses than I could ever have imagined it to be the first time I saw it bleaching in 1998. On the other hand, I realise that we have a limited window to change the narrative on tropical reefs. Without real and considered action on climate change, the reefs of Lakshadweep could well be functionally extinct in my lifetime -- and I cannot bear to think of what that would mean for my friends who call Lakshadweep their home,' said Rohan Arthur, Senior Scientist at the Nature Conservation Foundation who heads the Oceans and Coasts Programme.
'Many coral areas in our reefs are now dead. We have seen it first hand. The corals in the eastern end of Kavaratti are dead. This was seen after cyclone, Ockhi in 2017. We cannot express how we feel about this loss,' said Saheer Ali, diving instructor in Kavaratti.
The Indian Ocean basin, the fastest warming basin in the world, will see accelerated warming at a rate of 1.7 degree C-3.8°C per century during 2020-2100, a research paper published in Elsevier last year said. It also warned that this will lead to an increase in severe weather events, prolonged marine heatwaves and extreme Indian Ocean Dipole events that will influence the monsoon and cyclone development.
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Business Standard
21 hours ago
- Business Standard
2023's marine heatwaves signal early irreversible coral damage: Study
Marine heatwaves -- prolonged periods of raised ocean temperatures than what are typical for that time of year -- experienced in 2023 were not only unprecedented, but may have also signalled a potential climate tipping point, with irreversible, negative impacts to coral reefs and ecosystems, according to a new study. Researchers from China and the US found that regions in oceans across the globe, including the North Atlantic, and the tropical, south and north Pacific experienced extreme marine heatwaves -- the longest in duration, widest in extent and highest in intensity on record. The findings, published in the journal Science, show that the most intense warming occurred in the North Atlantic, tropical eastern Pacific, north Pacific, and southwest Pacific, which "collectively accounted for 90 per cent of the global ocean warming". Heatwaves in the North Atlantic which began mid-2022 persisted for 525 days with an intensity four times the typical, making it "the longest recorded marine heatwave in the region", the authors said. The southwest Pacific heat event broke records for its expanse and prolonged duration, while unusual temperatures in the tropical eastern Pacific peaked at 1.63 degrees Celsius during the onset of El Nino, they said. 'El Nino' is the warm phase of the 'El Nino-Southern Oscillation' (ENSO) natural climate pattern, which involves changes in temperatures and atmospheric pressures in the Pacific Ocean. El Nino is linked with warmer ocean temperatures. The authors, including those from the US' Scripps Institution of Oceanography at the University of California, said the marine heatwaves of 2023 were "a global event with a 50-year return period, (with a less than two per cent chance of occurrence)". First author Tianyun Dong, a joint postdoctoral researcher at the Eastern Institute of Technology, Ningbo, and Southern University of Science and Technology in China, told PTI in an email, "Global warming, observed over a long-term and primarily driven by greenhouse gas emissions, has raised the ocean's baseline state, making marine heatwaves increasingly frequent and intense." Further, the trends observed also suggest a "possible indication of an approaching climatic tipping point", the study said. A climate tipping point, potentially a 'point of no return', is related with irreversible, disproportionate health and economic consequences for the world's most vulnerable, such as tropical coral reefs, and ice sheets of Greenland and Antarctica. "While a full (ocean-climate) system collapse has not occurred, irreversible impacts -- mass coral bleaching in tropical reefs, collapse of key habitats -- are already emerging," Dong said. Coral bleaching in reefs, or the loss of algae in reefs causing a 'whitening' and vulnerability to disease and death, are showing few signs of recovering, while the functional collapse of key habitats in some of the world's regions undermine biodiversity and the role of ecosystems, Dong explained. "These impacts reflect more than a short-term stress, suggesting a shift towards a permanent ecological change. The 2023 marine heatwaves may, therefore, mark a dangerous step closer to tipping points in the ocean-climate system," the first author said. Arpita Mondal, associate professor at the department of civil engineering and centre for climate studies, IIT Bombay, and not involved with the study, told PTI, "Based on a primary reading of the paper, I'm quite convinced of the scientific robustness." Mondal explained that the ocean and atmosphere "talk to each other through processes -- called the 'teleconnections' -- through which far-away processes can influence local weather". "For example, processes in the southern and equatorial Pacific Ocean can influence the Indian monsoon," she said. "Of course, El Nino is the most significant phenomenon which affects not only monsoons in South Asia, but ENSO-neutral conditions -- where neither El Nino nor La Nina dominate -- have been linked with the heat waves in the pre-monsoon season too," Mondal explained. "Similarly, oscillations and circulation of currents in oceans and atmosphere can impact weather worldwide," she added. The study team analysed satellite observations and temperature data of the world's oceans. Data from the NASA-funded 'ECCO2' project, focussed on producing a high-resolution estimate of the state of the world's oceans and sea ice, was also analysed. First author Dong said that despite a relatively weak El Nino -- studies show its growth rate unexpectedly decelerated in mid-2023 -- the unprecedented nature of 2023's marine heatwaves cannot be explained by natural climate variability alone. "A continued warming of the planet -- especially when combined with El Nino -- could produce even more extreme marine heatwaves, pointing toward a potential new normal of amplified ocean heat extremes and a higher chance of crossing physical and ecological tipping points," the first author said. Mondal, who is not involved in the study, pointed to the concerning lack of reliable, long-term ocean data. "My concern is more about the lack of long-term, reliable ocean data globally. We have only been monitoring oceans in the recent years. We do not have say, 150 to 200 years of ocean surface temperatures recorded. However, satellites developed in the last 50 years or so have definitely helped in complementing the buoys which have been in place for monitoring the ocean," she said.
Hindustan Times
a day ago
- Hindustan Times
Lakshadweep's coral cover halved in 24 yrs
A 24-year-long study of corals in the Lakshadweep archipelago has found a 50% decline in coral cover compared to 1998 as a result of repeated marine heatwaves, exacerbated by climate change. The study published in the journal of Diversity and Distributions said this decline was explained by reduced recovery rates after each bleaching event, despite coral mortality decreasing with successive events. The paper concluded that the fate of corals in Lakshadweep will be determined by the return time of bleaching events. (HT photo) The paper concluded that the fate of corals in Lakshadweep will be determined by the return time of bleaching events, underscoring that urgent climate action is critical to secure the ecological integrity of tropical reefs. The scientists leading the study, including Rohan Arthur and Mayukh Dey from the Oceans and Coasts Programme of Nature Conservation Foundation concluded that 'the one thing reefs need to recover is time'. 'Without a pause in the frequency of marine heatwaves, whatever resilience tropical reefs have is likely to be short lived. Our results show that fewer corals die simply because less is available to die in later years,' they added. 'In the long run, we must call the crisis by its name and acknowledge that the integrity of tropical reefs, like the rest of global biodiversity, cannot sustain the seemingly impervious logic of the prevailing economic order. Without scale-appropriate radical policies, laws, and actions to address these ultimate causes, anything we do locally for reefs will be symptomatic and palliative fixes,' the scientists said. Lakshadweep Archipelago has 12 coral atolls in the northern Indian Ocean. The archipelago is among the most densely populated atoll systems globally with 10 populated islands, with more than 2000 people/sq km. Lakshadweep has experienced three marine heatwaves associated with the El Niño phase of the ENSO phenomena in 1998 (5.3 Degree Heating Weeks, DHW), 2010 (6.7 DHW) and 2016 (5.2 DHW), with 2010 being the most severe of the three. Hindustan Times, in a series on Lakshadweep published last year reported how the islands experienced a severe bleaching event in 2024. The heat stress in Lakshadweep (Laccadive Sea) and in Southeast India was record-setting in 2024 according to Derek P Manzello, Coordinator, NOAA Coral Reef Watch. The metric used to gauge heat stress on corals is called Degree Heating Weeks (DHW). DHW shows how much heat stress has accumulated in an area over the past 3 months. In 2024, Lakshadweep reached 9.2 DHWs, whereas SE India reached 9 DHWs. The prior record for Lakshadweep was 6.7 DHW in 2010, and it was 6.9 DHW for SE India in 2016, said Manzello. Since 1998, researchers from the Nature Conservation Foundation have been tracking reef conditions at three atolls across the Lakshadweep Archipelago , Agatti, Kadmat and Kavaratti , to understand how reefs respond to climate change. This monitoring programme has monitored reefs as they declined and recovered from three major El Niño Southern Oscillation (ENSO) events — in 1998, 2010 and 2016. The data was analysed to explore if changes in the composition of coral could be explained by the number of heatwaves experienced and by more local factors, such as seasonally strong wave action and depth at which corals are found. The team also found that these results challenge the simplistic narrative that all coral reefs respond in a similar fashion to climate change, and are universally doomed. Even within a small archipelago like Lakshadweep, there is a large variability in responses -- sometimes in reefs only a few kilometres apart. 'The Lakshadweep reefs have been home to me since I first dived here as a young researcher. To see these diverse ecosystems decline before my eyes is soul-destroying. Our findings are a bittersweet offering. On the one hand, it shows me that the reef is more complex and more resilient in its responses than I could ever have imagined it to be the first time I saw it bleaching in 1998. On the other hand, I realise that we have a limited window to change the narrative on tropical reefs. Without real and considered action on climate change, the reefs of Lakshadweep could well be functionally extinct in my lifetime -- and I cannot bear to think of what that would mean for my friends who call Lakshadweep their home,' said Rohan Arthur, Senior Scientist at the Nature Conservation Foundation who heads the Oceans and Coasts Programme. 'Many coral areas in our reefs are now dead. We have seen it first hand. The corals in the eastern end of Kavaratti are dead. This was seen after cyclone, Ockhi in 2017. We cannot express how we feel about this loss,' said Saheer Ali, diving instructor in Kavaratti. The Indian Ocean basin, the fastest warming basin in the world, will see accelerated warming at a rate of 1.7 degree C-3.8°C per century during 2020-2100, a research paper published in Elsevier last year said. It also warned that this will lead to an increase in severe weather events, prolonged marine heatwaves and extreme Indian Ocean Dipole events that will influence the monsoon and cyclone development.
The Hindu
2 days ago
- The Hindu
24-year study reveals that coral cover in Lakshadweep saw 50% reduction
Concerning revelations have emerged from one of the longest-running coral reef monitoring programmes in the Indian Ocean. The 24-year-long study shows that corals in the Lakshadweep archipelago have declined to half of what they were in 1998 as a result of repeated marine heatwaves, exacerbated by climate change. However, local conditions, such as wave exposure and depth, play essential roles in shaping how reefs respond to and recover from these events. The study, 'Local Environmental Filtering and Frequency of Marine Heatwaves Influence Decadal Trends in Coral Composition', published in the journal Diversity and Distributions, uses long-term data sets to propose a predictive framework, which could help identify vulnerable reefs, and reefs that may still have the potential to recover. Since 1998, researchers from the Nature Conservation Foundation have been tracking reef condition at three atolls across the Lakshadweep archipelago — Agatti, Kadmat and Kavaratti — to understand how reefs respond to climate change. This monitoring programme has monitored reefs as they declined and recovered from three major El Niño Southern Oscillation (ENSO) events — in 1998, 2010 and 2016. The data was analysed to explore if changes in the composition of coral could be explained by the number of heatwaves experienced and by more local factors, such as seasonally strong wave action and depth at which corals are found. Reduced recovery rate 'Over 24 years, coral cover declined from 37.24% to 19.6%, reflecting a roughly 50% reduction from the 1998 baseline. This decline was explained by reduced recovery rates after each bleaching event, despite coral mortality decreasing with successive events. Recovery rates dramatically increased after six years, suggesting a critical period of bleaching-free years needed for reefs to recover. We observed contrasting responses of coral genera, which clustered in six groups representing distinct assemblage-wide patterns in distribution (depth and wave exposure) and bleaching responses. Genera with different life histories clustered together, highlighting the importance of local environments in determining the survival and recovery of corals across taxa,' the researchers stated. Species are expected to respond to disturbances according to their biological characteristics (life history traits), and the researchers expected that corals in Lakshadweep reefs will closely track their biology, as has been suggested by other studies, resulting in a clear set of winners and losers on the reef. 'What we found was much more nuanced. Over the 24 years of change, we identified not just two group of winners or losers, but six distinct kinds of responses (or clusters), based on how corals were affected by heatwaves, their recovery time, the depth at which they were found, and whether they grew on exposed or sheltered reefs. Importantly, these clusters are a useful predictive framework, which we can use to map other reefs across the archipelago and possibly beyond, to determine their susceptibility to climate change. This work offers an unprecedented tool to assist classifying corals based on their ability to resist and recover from future bleaching events, which can lead to meaningful spatial planning in the face of climate change — something that was unavailable for this region until now,' they stated. Time is of essence The researchers warn that no amount of local resilience and restoration efforts, especially in regions that do not support corals that make up a resilient cluster, can substitute urgent global climate action: 'The one thing reefs need to recover is time. Without a pause in the frequency of marine heatwaves, whatever resilience tropical reefs have is likely to be short lived. Our results show that less corals die simply because less is available to die in later years. In the long run, we must call the crisis by its name and acknowledge that the integrity of tropical reefs, like the rest of global biodiversity, cannot sustain the seemingly impervious logic of the prevailing economic order. Without scale-appropriate radical policies, laws, and actions to address these ultimate causes, anything we do locally for reefs will be symptomatic and palliative fixes.'
