Scientists have launched the world’s first system to detect in near real time the whitening of the planet’s coral reefs, which are under severe threat of global warming.
The developers of the new tool, created four years ago, claim it can allow anyone to check if reefs known under heat stress have actually started to whiten.
Coral reefs, which support the livelihoods of hundreds of millions of people and are home to about a quarter of all ocean species, are one of the ecosystems most threatened by global warming.
The United Nations climate estimate says coral reefs will decline by between 70% and 90% even if global warming remains at 1.5C.
Massive bleaching events that are becoming more common can weaken corals or, in severe cases, kill them over large areas.
The new tool, funded by Vulcan Inc, the company founded by the late Microsoft co-founder Paul Allen, could reveal the full extent of bleaching worldwide as well as reveal spots where corals survive.
Currently the U.S. government agency the National Oceanic and Atmospheric Administration is making predictions about the likelihood of whitening around the world by models and measurements of satellite sea surface temperatures.
Prof Greg Asner, the managing director of the Allen Coral Atlas, which launched the tool, said his team developed and tested it during two bleaching events – one severe explosion in French Polynesia in early 2019 and another milder bleaching in Hawaii, where he is based, later the same year.
He said the team of developers – at Arizona State University, the University of Queensland, National Geographic Society, satellite company Planet and Volcano – worked out how to overcome two major problems: clouds obstructing the satellite and the road. light changes as it travels through water and the atmosphere.
The tool collects and combines images over six days, reducing the chances of clouds obscuring the satellite’s view.
Asner, of Arizona State University, wants the new tool to be used by governments and reef managers around the world to help target conservation efforts.
Using two sets of satellite images – one from a constellation of small satellites and another from two larger satellites – the tool archives daily images of coral reefs mapped by the University of Queensland.
By comparing different sets of images of coral reefs before they whiten, the tool detects the dramatic color changes that are characteristic of coral bleaching.
Bleaching is a stressful reaction. If corals sit in unusually warm water for too long, they separate from the colored algae that give most nutrients.
For now, Asner said the tool will be refreshed every two weeks and will focus on areas that the NOAA Coral Reef Warning warns are under threat.
He said in addition to being able to see where corals have turned white, the tool can also identify areas that do not turn white – known as refuges.
“Knowing where these shelters are will be really important,” he said, adding that this could help governments identify where to conduct research or conservation efforts.
It is planned to further develop the Allen Coral Atlas to detect other threats to coral reefs due to pollution escaping from the land.
Asner added: “Science shows us those areas [of coral reefs] which get twice as much heat and pollution much worse. “
Quickly cutting greenhouse gas emissions was essential, Asner said, because there are still healthy coral reefs around the world that could be saved.
Reefs are controlled in many ways – from underwater surveys and citizen scientific efforts, to autonomous underwater gliders with built-in thermometers or control flights in aircraft.
Dr Manuel Gonzalez Rivero, who leads the reef monitoring team at the Australian Institute of Marine Science, said the tool is a “significant step forward”.
“This is a resource that has never existed before. What this does allows us to truly understand how much the impact is [of heat stress] translates across large areas. “
He said Targets – the Australian government’s marine science agency – has been working with Allen Coral Atlas and will use the new tool.
Current tools use meteorological forecasts and calculations of heat stress on corals to give bleaching warnings.
“But that doesn’t give us a complete picture. This for me is a significant step forward where we are at the moment. Having real-time information can help us with our more responsive monitoring. “
The ability of corals to tolerate extra heat varies between species. There is evidence that the composition of corals on reefs has already changed, with less tolerant species more scarce.
“This will document something that will paint a difficult picture of what is happening and that will be difficult. But the thing is, understanding the principle of whitening can help us be more enterprising. “
The tool relies on detailed maps of more than 230,000 reefs and their environs, about 140,000 square kilometers developed at the University of Queensland’s Remote Sensing Research Center. This mapping tells the tool where on the planet it should look for changes.
Dr Chris Roelfsema, of the research center, said the maps cover about 82% of the world’s reefs.
He said: “So far there is no global system to control coral reefs under the stresses that can lead to their deaths.”
Roelfsema’s team was already mapping the Great Barrier Reef when Asner’s team asked them about four years ago if they could cover the entire globe.
“It was an exciting question. These satellites – some are 700km above the earth – and the Planetary satellites are just as big as a microwave.
“Five or 10 years ago we couldn’t have done this. The ability just wasn’t. “