Bleached coral


Coral reefs around the world are currently facing bleaching and die-offs, largely due to escalating ocean temperatures.

This disturbing phenomenon has prompted the US National Oceanic and Atmospheric Administration (NOAA) to declare the onset of the fourth global mass coral bleaching event.

Bleaching occurs when corals, stressed by elevated water temperatures, expel the symbiotic algae living in their tissues, causing them to turn white. This algae is crucial for coral health, providing them with food through photosynthesis. Without it, corals not only lose their colour but also their main source of nourishment, making them more susceptible to disease and death.

The economic and ecological stakes are high. Coral reefs are vital to marine biodiversity, supporting approximately 25% of all marine species. They also bolster coastal protection, tourism, and fishing industries, generating trillions of dollars annually in economic value.

Recent months have seen consecutive ocean heat records being shattered, a clear indicator of how climate change, fuelled by the burning of fossil fuels and subsequent warming gases, is impacting our oceans. An added factor exacerbating this year’s ocean temperatures is El Niño, a natural climatic phenomenon that causes global temperatures to rise.

Reports from scientists across the globe, including those from the United States, Australia, Kenya, and Brazil, have been flowing in, documenting extensive bleaching across all oceans. Notable areas impacted include the Great Barrier Reef in Australia, coral reefs off the coasts of Tanzania, Mauritius, Brazil, the Pacific islands, and even regions such as the Red Sea and Persian Gulf.

For instance, Neal Cantin from Australia’s Institute of Marine Science recently undertook aerial surveys over the Great Barrier Reef, a UNESCO World Heritage site, only to find extensive bleaching along this vital marine ecosystem.

“For the first time ever we’ve documented very high levels of bleaching in all three areas of the Great Barrier Reef Marine Park,” Dr Cantin says. The levels are likely to kill lots of coral, he adds.

The situation has not only alarmed scientists but also local communities that depend on these ecosystems. In regions like the Indian Ocean, ecologist David Obura notes that local fishermen can immediately detect changes in coral health, which directly impacts their fish catch and by extension, their livelihoods.

Despite the dire situation, not all hope is lost. Research indicates that corals in deeper, cooler waters might have a better chance of surviving the increasing temperatures. Studies suggest these deeper reefs could potentially withstand global warming scenarios better than their shallow-water counterparts.

Nevertheless, coral experts are united in their view that small-scale reef restoration cannot combat the global scale of the threat. The consensus is clear: only a significant, global reduction in greenhouse gas emissions can curb ocean warming sufficiently to preserve at least some of the world’s coral reefs.

Coral can recover from heat stress but it needs time – ideally several years. When it becomes weakened it is susceptible to disease and death.

“If given a chance, coral are actually resilient and can recover. But as bleaching becomes more frequent and stronger in intensity, we’re really narrowing that window,” says Dr Emma Camp at the University of Technology Sydney, Australia.

The alarming pace of change has even led NOAA to introduce three new heat alert levels since the last mass bleaching event in 2014-2016. The current conditions underscore the urgent need for action to save these vital ecosystems.

Anne Hoggett, a scientist who has spent decades studying the reefs around Australia’s Lizard Island, has observed the devastating transformation of vibrant reefs into bleached wastelands. Her experiences reflect a broader trend of increasing ocean temperatures and subsequent coral stress, which can lead to widespread coral mortality if conditions persist or worsen.

The impacts of coral loss extend beyond the reefs themselves. Fish and other marine species that rely on coral reefs for food and habitat face an uncertain future if the structural complexity and biodiversity of these ecosystems continue to decline.

“It’s like going from corals providing houses and buildings for marine life to just being scaffolding. What really wants to live in scaffolding?” Dr McWhorter says.Coral reefs are an early warning system for the impacts of a warming planet on nature. “We need to learn from this to not do this to other ecosystems,” says Dr Obura.



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