*[Enwl-eng] 'Heroic effort' as scientists race to rescue corals
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No images? Click here  If this summer has felt hot for many people on land then imagine how it has felt in the ocean, where 90% of the excess heat generated by greenhouse gas emissions has been absorbed. El Niño, the hot phase of a natural cycle in the Pacific Ocean which influences weather worldwide, has amplified global heating during 2023 to make the ocean hotter than at any other time in modern history. As seawater in some regions has approached hot-tub temperatures, scientists have fretted over coral reefs, ecosystems which harbour the greatest concentration of species in the ocean. Many of these bastions of marine biodiversity have endured overfishing, pollution and creeping acidification. Is record ocean heat in 2023 the final straw? You're reading the Imagine newsletter – a weekly synthesis of academic insight on solutions to climate change, brought to you by The Conversation. I'm Jack Marley, energy and environment editor. This week, we hear from conservationists who are racing to save coral reefs from increasingly hostile conditions. Tropical coral reefs are astonishingly resilient. New research reveals how these ecosystems – composed of tiny animal polyps in a limestone skeleton they share with photosynthetic algae – have managed to thrive in low-nutrient waters for millions of years. As well as catching plankton with their tentacles and living off the sugars their algal cohabitants make via photosynthesis, corals can eat the algae living in their cells to acquire growth-boosting nitrogen and phosphorous. "This vegetarian diet allows the corals to tap into a large pool of nutrients that was previously considered unavailable to them," say authors Jörg Wiedenmann and Cecilia D'Angelo at the University of Southampton. While well adapted to a challenging environment, tropical corals have had to contend with rapid changes in recent years. "A paper by [US] scientist Derek Manzello showed that in the Florida Keys, the number of days per year in which water temperatures were higher than 90°F (32°C) had increased by more than 2,500% in the two decades following the mid-1990s relative to the prior 20 years," says Ian Enochs, who leads coral research at a National Oceanic and Atmospheric Administration (NOAA) lab in Miami, Florida. "That is a remarkable increase in the number of days that corals are experiencing particularly stressful warm water." When corals are stressed for long enough they bleach: their colourful algae departs and the remaining reef turns pale and can eventually starve or succumb to disease, eroding to sand over time. A paper by Enochs' colleague John Morris found that 70% of reefs in the Florida Keys are now eroding faster than they are growing. Marine heat waves (prolonged bouts of high sea temperatures) may last weeks, but the damage they cause to reefs can be permanent. Samuel Starko at the University of Western Australia and Julia K. Baum at the University of Victoria studied the aftermath of El Niño-driven bleaching on Kiritimati (Christmas Island) in the central Pacific Ocean between 2015 and 2016. "We focused on the widespread lobed coral (Porites lobata). This species is among the most heat-tolerant corals, and despite almost 90% of all coral cover being lost on Kiritimati, over half of lobed corals survived," they say. "In fact, some Porites colonies didn’t bleach at all." Scientists have found surprisingly hardy coral species in other regions too. The survival of these remnants may maintain the illusion of a healthy ecosystem – but dwindling species are a problem in their own right. "Because interbreeding between ... lineages and species can offer a potential avenue for future adaptation, losses of genetic diversity could make a bad problem even worse by limiting future adaptation to changing environments," they say. An emergency response The overwhelming odds against coral reefs have not deterred researchers. Michael Childress, an associate professor of biology and conservation at Clemson University, describes the "heroic efforts" of scientists who sprung into action as a heat wave unravelled across the Caribbean in June. "Divers have been in the water every day, collecting thousands of corals from ocean nurseries along the Florida Keys reef tract and moving them to cooler water and into giant tanks on land," he says. Corals can recover their algal companions if water temperatures return to normal within a few weeks. The volunteers, students and government scientists removing seaweed and predators encroaching reefs in the Florida Keys and rescuing coral fragments grown in underwater nurseries could buy these ecosystems precious time. New research findings from reefs in the remote Pacific suggest these efforts might not be in vain. Over 35 years, an international team of scientists discovered that coral communities in Palau have increased their tolerance of higher temperatures by 0.1°C a decade. "That’s slightly less than the increase in global temperatures (about 0.18°C/decade) but does suggest these coral reefs have an innate capacity for climate resilience," says author Liam Lachs, a PhD candidate in climate change ecology and evolution at Newcastle University. This means that there is a brief window in which people intervening to limit local threats to reefs could help corals weather a peak in global temperatures. "But this can only improve their long-term futures if there is strong global action on reducing carbon emissions," Lachs says. So far, countries have not responded to the worsening plight of coral reefs by slashing their emissions of carbon dioxide, which overwhelmingly come from burning fossil fuels. Australia hosts the world's largest reef. Despite being elected with a pledge to take drastic action on climate change, its government approved a new coal mine in May. "And still we fail to face up to the fact that the Great Barrier Reef is dying," says Ove Hoegh-Guldberg, a professor of marine science at the University of Queensland. "We thought we might have had decades but it may be just years. Before 1980, no mass bleaching had ever been recorded. Since then it has only become more common." - Jack Marley, Environment commissioning editor Was this email forwarded to you? Join the 20,000 people who get one email every week about the most important issue of our time. Subscribe to Imagine.  Ocean temperatures have hit record highs off the Florida Keys. Scientists and volunteer divers are racing to save these valuable creatures.  Corals are starting to bleach as global ocean temperatures hit record highs Water temperatures in the 90s off Florida in July are alarming, a NOAA coral scientist writes. Scientists in several North American countries have already spotted coral bleaching off their coasts.  Remote Pacific coral reef shows at least some ability to cope with ocean warming – new study This may buy us time, but many reefs are still doomed without serious action on climate change.  Reef corals grow vigorously in nutrient-poor water – new research has found out why.  Coral reefs: How climate change threatens the hidden diversity of marine ecosystems Exploring the often unseen, and poorly understood, nuances of diversity within coral reefs may prove essential for ensuring the long-term health of Earth's oceans.  Is the Great Barrier Reef reviving – or dying? Here’s what’s happening beyond the headlines In recent years, the Barrier Reef has had a reprieve – and coral has regrown strongly. But now the reprieve looks to be over and the heat is back on. Latest from The Conversation on climate change
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