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Earth's fourth global coral bleaching event is CONFIRMED: Scientists warn once brightly-coloured reefs across the Atlantic, Pacific, and Indian Oceans have been bleached white by record water temperatures
There's nothing quite like seeing a myriad of fish dart in and out of brightly-coloured reefs.
But coral across the Atlantic, Pacific and Indian Oceans has turned white as the world's fourth global bleaching event has been confirmed.
The change, caused by heat stress, is linked to climate change and rising ocean temperatures as well as low tides, pollution or too much sunlight.
And experts have warned that, unless there is a global effort to help the coral recover, it will turn black and die.
'As the world's oceans continue to warm, coral bleaching is becoming more frequent and severe,' Derek Manzello, NOAA Coral Reef Watch coordinator, said.
There's nothing quite like seeing a myriad of fish dart in and out of brightly-coloured reefs. But coral across the Atlantic, Pacific and Indian Oceans has turned white as the World's fourth global bleaching event has been confirmed. Pictured: Coral bleaching in American Samoa
Healthy coral is coated with an algae-like substance called zooxanthellae, which they depend on to survive.
When coral becomes too stressed from changes in its environment, the coating can become toxic and leave the coral – turning it white and leaving it vulnerable to starvation, disease and death.
A report, published by the International Coral Reef Institute (ICRI), reveals that since 2023 there has been confirmation of mass bleaching of coral reefs in at least 53 countries, territories and local economies.
This includes Florida, the Caribbean, the Eastern Tropical Pacific including Mexico, El Salvador, Costa Rica, Panama, and Colombia, Australia's Great Barrier Reef, large areas of the South Pacific including Fiji, Vanuatu, Tuvalu, Kiribati, and the Samoas, the Red Sea, the Persian Gulf and the Gulf of Aden.
Reports have also been confirmed of widespread bleaching across parts of the Western Indian Ocean, including Tanzania, Kenya, Mauritius, the Seychelles, Tromelin, Mayotte, and off the western coast of Indonesia. The monitoring of coral reefs is carried out by the National Oceanic and Atmospheric Administration (NOAA).
The change, caused by heat stress, is linked to climate change and rising ocean temperatures as well as low tides, pollution or too much sunlight. Pictured: coral bleaching on Heron Island, Great Barrier Reef
Experts have warned that, unless there is a global effort to help the coral recover, the coral will turn black and die. Pictured: Coral bleaching on the Great Barrier Reef
Mr Manzello said: 'From February 2023 to April 2024, significant coral bleaching has been documented in both the Northern and Southern hemispheres of each major ocean basin.
'When these events are sufficiently severe or prolonged, they can cause coral mortality, which can negatively impact the goods and services coral reefs provide that people depend on for their livelihoods.'
Widespread coral death can impact livelihoods, food security and economies, including local tourism and the commercial fishing industry.
However, researchers said that it is important to remember that coral bleaching does not always lead to coral death.
Widespread coral death can impact livelihoods, food security and economies, including local tourism and the commercial fishing industry. Pictured: knobby cactus coral in the Virgin Islands in July 2023, November 2023, and March 2024
However, researchers said that it is important to remember that coral bleaching does not always lead to coral death. Pictured: large flower coral in the Virgin Islands in April 2022, November 2023, and March 2024
If the stress driving the bleaching diminishes, corals can recover – allowing reefs to bounce back.
In 2019, NOAA published a plan to help coral reefs in distress.
This was implemented during the 2023 heatwave in Florida, when coral nurseries were moved to deeper, cooler waters and sunshades were erected to protect corals from the sun.
Jennifer Koss, director of NOAA's Coral Reef Conservation Program, said: 'Climate model predictions for coral reefs have been suggesting, for years, that bleaching impacts would increase in frequency and magnitude as the oceans warm.
If the stress driving the bleaching diminishes, corals can recover – allowing reefs to bounce back. Pictured: Coral bleaching on the Great Barrier Reef
Figures suggest that since the 1950s, more than 50 per cent of the world's coral reefs have died, with predictions that up to 90 per cent may die within the next century. Pictured: Coral bleaching in American Samoa
'We are on the frontlines of coral reef research management and restoration, and are actively and aggressively implementing the recommendations of the 2019 Interventions Report.'
Figures suggest that since the 1950s, more than 50 per cent of the world's coral reefs have died, with predictions that up to 90 per cent may die within the next century.
Thousands of marine animals including turtles, crabs and starfish depend on coral reefs for survival as they provide shelter, spawning grounds and protection from predators.
WHAT ARE MARINE HEATWAVES AND WHAT DO WE KNOW ABOUT THEM?
On land, heatwaves can be deadly for humans and wildlife and can devastate crops and forests.
Unusually warm periods can also occur in the ocean. These can last for weeks or months, killing off kelp forests and corals, and producing other significant impacts on marine ecosystems, fishing and aquaculture industries.
Yet until recently, the formation, distribution and frequency of marine heatwaves had received little research attention.
Long-term change
Climate change is warming ocean waters and causing shifts in the distribution and abundance of seaweeds, corals, fish and other marine species. For example, tropical fish species are now commonly found in Sydney Harbour.
But these changes in ocean temperatures are not steady or even, and scientists have lacked the tools to define, synthesize and understand the global patterns of marine heatwaves and their biological impacts.
At a meeting in early 2015, we convened a group of scientists with expertise in atmospheric climatology, oceanography and ecology to form a marine heatwaves working group to develop a definition for the phenomenon: A prolonged period of unusually warm water at a particular location for that time of the year. Importantly, marine heatwaves can occur at any time of the year, summer or winter.
Unusually warm periods can last for weeks or months, killing off kelp forests and corals, and producing other significant impacts on marine ecosystems, fishing and aquaculture industries worldwide (pictured)
With the definition in hand, we were finally able to analyse historical data to determine patterns in their occurrence.
Analysis of marine heatwave trends
Over the past century, marine heatwaves have become longer and more frequent around the world. The number of marine heatwave days increased by 54 per cent from 1925 to 2016, with an accelerating trend since 1982.
We collated more than 100 years of sea surface temperature data around the world from ship-based measurements, shore station records and satellite observations, and looked for changes in how often marine heatwaves occurred and how long they lasted.
This graph shows a yearly count of marine heatwave days from 1900 to 2016, as a global average.
We found that from 1925 to 1954 and 1987 to 2016, the frequency of heatwaves increased 34 per cent and their duration grew by 17 per cent.
These long-term trends can be explained by ongoing increases in ocean temperatures. Given the likelihood of continued ocean surface warming throughout the 21st century, we can expect to see more marine heatwaves globally in the future, with implications for marine biodiversity.
'The Blob' effect
Numbers and statistics are informative, but here's what that means underwater.
A marine ecosystem that had 30 days of extreme heat in the early 20th century might now experience 45 days of extreme heat. That extra exposure can have detrimental effects on the health of the ecosystem and the economic benefits, such as fisheries and aquaculture, derived from it.
A number of recent marine heatwaves have done just that.
In 2011, a marine heatwave off western Australia killed off a kelp forest and replaced it with turf seaweed. The ecosystem shift remained even after water temperatures returned to normal, signalling a long-lasting or maybe even permanent change.
That same event led to widespread loss of seagrass meadows from the iconic Shark Bay area, with consequences for biodiversity including increased bacterial blooms, declines in blue crabs, scallops and the health of green turtles, and reductions in the long-term carbon storage of these important habitats.
Examples of marine heatwave impacts on ecosystems and species. Coral bleaching and seagrass die-back (top left and right). Mass mortality and changes in patterns of commercially important species s (bottom left and right)
Similarly, a marine heatwave in the Gulf of Maine disrupted the lucrative lobster fishery in 2012. The warm water in late spring allowed lobsters to move inshore earlier in the year than usual, which led to early landings, and an unexpected and significant price drop.
More recently, a persistent area of warm water in the North Pacific, nicknamed 'The Blob', stayed put for years (2014-2016), and caused fishery closures, mass strandings of marine mammals and harmful algal bloom outbreaks along the coast. It even changed large-scale weather patterns in the Pacific Northwest.
As global ocean temperatures continue to rise and marine heatwaves become more widespread, the marine ecosystems many rely upon for food, livelihoods and recreation will become increasingly less stable and predictable.
The climate change link
Anthropogenic, that is human-caused, climate change is linked to some of these recent marine heatwaves.
For example, human emissions of greenhouse gases made the 2016 marine heatwave in tropical Australia, which led to massive bleaching of the Great Barrier Reef, 53 times more likely to occur.
Even more dramatically, the 2015-16 marine heatwave in the Tasman Sea that persisted for more than eight months and disrupted Tasmanian fisheries and aquaculture industries was over 300 times more likely, thanks to anthropogenic climate change.
For scientists, the next step is to quantify future changes under different warming scenarios. How much more often will they occur? How much warmer will they be? And how much longer will they last?
Ultimately, scientists should develop forecasts for policy makers, managers and industry that could predict the future impacts of marine heatwaves for weeks or months ahead. Having that information would help fishery managers know when to open or close a fishery, aquaculture businesses to plan harvest dates and conservation managers to implement additional monitoring efforts.
Forecasts can help manage the risks, but in the end, we still need urgent action to curb greenhouse gas emissions and limit global warming. If not, marine ecosystems are set for an ever-increasing hammering from extreme ocean heat.
Source: Eric Oliver, Assistant Professor, Dalhousie University; Alistair Hobday, Senior Principal Research Scientist - Oceans and Atmosphere, CSIRO; Dan Smale, Research Fellow in Marine Ecology, Marine Biological Association; Neil Holbrook, Professor, University of Tasmania; Thomas Wernberg, ARC Future Fellow in Marine Ecology, University of Western Australia in a piece for The Conversation.
