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Hindustan Times
2 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.
Glasgow Times
19-05-2025
- Science
- Glasgow Times
Habitat in many estuaries at high risk of being ‘squeezed' out by climate change
Estuaries are key for wildlife such as wading birds, as breeding and nursery grounds for commercially important fish, and for storing carbon and improving water quality by filtering nutrients, contaminants and sediment. However, a combination of rising seas and lower summer river levels as a result of climate change, and man-made barriers such as weirs and dams are putting freshwater habitat at the top of estuaries at risk, according to scientists who have previously coined the phenomenon 'estuarine squeeze'. Now researchers have identified and mapped the tidal freshwater and brackish zones with low salt levels – important areas which provide habitat and corridors for nutrients and wildlife – at the top of all 85 estuaries in mainland England and Wales. Nearly 70% of these estuaries are blocked by barriers such as weirs or sluices where the estuary meets the river, and around half contain tidal freshwater and brackish zones, the analysis shows. The Exe estuary in Devon is also one of those threatened (Emily Beament/PA) Some 19 estuaries with tidal freshwater and brackish zones had barriers preventing them shifting inland as the seas rise and push salty water further in. This puts them at high risk of 'estuarine squeeze' and potentially the complete loss of the important habitats, the researchers warn. The Medway, Exe and Ouse estuaries in the south of England were identified as most at risk, the study published in the journal Estuarine, Coastal and Shelf Science found. But the researchers from Nottingham Trent University said the findings also show the opportunity to recreate the wildlife-rich tidal freshwater marshes and wet woodlands that once lined the top of many of the UK's estuaries – lost over the centuries to drainage for agriculture and development. Recreating these marshes in the right estuaries would help combat estuarine squeeze, while also helping to improve water quality, store carbon and boost wildlife such as endangered European eels and migrating water birds. There is 'significant scope' for creating marshes on the tidal River Trent and River Great Ouse, recreating fenland habitats which would have once supported eel populations but have been drained. While it is 'clearly not cost-effective' to recreate marsh habitat in estuaries where the tidal freshwater zone is at risk of being rapidly squeezed out, the researchers argue their study could be used to identify locations where marsh creation could have the most benefit. Recreating tidal freshwater marshes in estuaries which do not have boundaries such as weirs at the top could compensate for where habitat at risk of being lost to estuarine squeeze, they say. They point to the Axe, Otter, Avon and Erme estuaries in south-west England which are near to some of the estuaries identified here as being most susceptible to estuarine squeeze. But the researchers also say removal of barriers or projects to create 'bypass channels' could become a priority in rivers and estuaries at risk of losing their tidal freshwater areas. Dr Sally Little, an estuarine ecologist at Nottingham Trent University, said: 'Tidal freshwater and low salinity zones at the top of our estuaries are crucial. 'They are home to many different plants and animals, are productive, help store carbon, cycle nutrients and improve water quality. 'They are also critical habitat and corridors for migratory fish moving between river and sea. 'Many of these zones are being squeezed due to climate change and development, and we now risk losing some of them completely. 'Our study underscores the urgent need for monitoring and management, but it also presents a unique opportunity to compensate for their loss through the creation of tidal freshwater marshes,' she said. She added that tidal freshwater marshes have been showed to have similar or larger potential for storing carbon and providing natural services than saltmarshes, where much of the focus for restoring coastal habitat has been.
Western Telegraph
18-05-2025
- Science
- Western Telegraph
Habitat in many estuaries at high risk of being ‘squeezed' out by climate change
Estuaries are key for wildlife such as wading birds, as breeding and nursery grounds for commercially important fish, and for storing carbon and improving water quality by filtering nutrients, contaminants and sediment. However, a combination of rising seas and lower summer river levels as a result of climate change, and man-made barriers such as weirs and dams are putting freshwater habitat at the top of estuaries at risk, according to scientists who have previously coined the phenomenon 'estuarine squeeze'. Now researchers have identified and mapped the tidal freshwater and brackish zones with low salt levels – important areas which provide habitat and corridors for nutrients and wildlife – at the top of all 85 estuaries in mainland England and Wales. Nearly 70% of these estuaries are blocked by barriers such as weirs or sluices where the estuary meets the river, and around half contain tidal freshwater and brackish zones, the analysis shows. The Exe estuary in Devon is also one of those threatened (Emily Beament/PA) Some 19 estuaries with tidal freshwater and brackish zones had barriers preventing them shifting inland as the seas rise and push salty water further in. This puts them at high risk of 'estuarine squeeze' and potentially the complete loss of the important habitats, the researchers warn. The Medway, Exe and Ouse estuaries in the south of England were identified as most at risk, the study published in the journal Estuarine, Coastal and Shelf Science found. But the researchers from Nottingham Trent University said the findings also show the opportunity to recreate the wildlife-rich tidal freshwater marshes and wet woodlands that once lined the top of many of the UK's estuaries – lost over the centuries to drainage for agriculture and development. Recreating these marshes in the right estuaries would help combat estuarine squeeze, while also helping to improve water quality, store carbon and boost wildlife such as endangered European eels and migrating water birds. There is 'significant scope' for creating marshes on the tidal River Trent and River Great Ouse, recreating fenland habitats which would have once supported eel populations but have been drained. While it is 'clearly not cost-effective' to recreate marsh habitat in estuaries where the tidal freshwater zone is at risk of being rapidly squeezed out, the researchers argue their study could be used to identify locations where marsh creation could have the most benefit. Recreating tidal freshwater marshes in estuaries which do not have boundaries such as weirs at the top could compensate for where habitat at risk of being lost to estuarine squeeze, they say. They point to the Axe, Otter, Avon and Erme estuaries in south-west England which are near to some of the estuaries identified here as being most susceptible to estuarine squeeze. But the researchers also say removal of barriers or projects to create 'bypass channels' could become a priority in rivers and estuaries at risk of losing their tidal freshwater areas. Many of these zones are being squeezed due to climate change and development, and we now risk losing some of them completely Dr Sally Little, Nottingham Trent University Dr Sally Little, an estuarine ecologist at Nottingham Trent University, said: 'Tidal freshwater and low salinity zones at the top of our estuaries are crucial. 'They are home to many different plants and animals, are productive, help store carbon, cycle nutrients and improve water quality. 'They are also critical habitat and corridors for migratory fish moving between river and sea. 'Many of these zones are being squeezed due to climate change and development, and we now risk losing some of them completely. 'Our study underscores the urgent need for monitoring and management, but it also presents a unique opportunity to compensate for their loss through the creation of tidal freshwater marshes,' she said. She added that tidal freshwater marshes have been showed to have similar or larger potential for storing carbon and providing natural services than saltmarshes, where much of the focus for restoring coastal habitat has been.
