World Oceans Day: Coral reefs experiencing bleaching - Scientists

Coral reefs around the world are experiencing global bleaching for the fourth time, a result of warming ocean waters amid human-caused climate change according to scientists.

Coral reef bleaching across at least 53 countries, territories or local economies has been confirmed from February 2023 to now, scientists from the National Oceanic and Atmospheric Administration and International Coral Reef Initiative reported in April.

In order for bleaching to be declared on a global scale, significant bleaching had to be documented within each of the major ocean basins, including the Atlantic, Pacific, and Indian oceans, in both the Northern and Southern Hemispheres.

Bleaching happens when stressed coral expel the algae that are their food source and give them their colour. If the bleaching is severe and long-lasting, the coral can die.

Bleaching has been happening in various regions for some time.

In the world’s largest coral reef ecosystem, Australia’s Great Barrier Reef, bleaching affected 90% of the coral assessed in 2022.

In March 2024 Great Barrier Reef Marine Park Authority announced a mass coral bleaching event following aerial surveys.

Scientists observed coral bleaching on 73 per cent of surveyed reefs within the Marine Park according to the Great Barrier Reef Marine Park Authority website.

“The reality for what's happening in the Great Barrier Reef unfortunately, isn't a surprise, and it's a consequence of rising global temperatures, and we're very certain of that, partly because of the science, but also because of what we've seen across the whole of the last 12 months,” says Roger Beeden, Great Barrier Reef Marine Park Authority Chief Scientist.

The reef has experienced “unprecedented temperatures, widespread coral bleaching seen in all the areas, likely to be at least on par with the substantial events that we saw in 2016 and 2017,” adds Beeden.

The world is experiencing the second global bleaching event in the last 10 years.

The last one ended in May 2017. Brought on by a powerful El Nino climate pattern that heated the world’s oceans, it lasted three years and was determined to be worse than the prior two bleaching events in 2010 and 1998.

This year’s bleaching follows the declaration that 2023 was the hottest year on record.

The Florida Coral Reef, the third-largest, experienced significant bleaching last year.

In the Atlantic, off the Florida coast and in the Caribbean, about 99.7% of the coral reefs have been hit with “very very severe’’ losses in staghorn and elkhorn species according to the NOAA.

"The situation right now is pretty dire. We are in the 11th hour of - in many places with mass coral bleaching all over the entire world. We're right now in the fourth global mass bleaching event. So make no mistake about it, situation is grim," says Ian Enochs, a research ecologist at NOAA's Atlantic Oceanographic and Meteorological Laboratory, leading the Coral Program.

However Enochs and other scientists around the world are working to reverse the trend and grow corals in labs for replanting.

" I have not lost all hope. There are still things that we can do to turn this around," he adds.

Enoch's work focuses on understanding the impacts of heat stress on coral reefs.

"So we know that we can make corals stronger, more capable of dealing with thermal stress. This is something that I'm doing in my lab right now, stress hardening. We also know that we can identify individuals that are particularly strong, that are capable of dealing with that stress already. Again, something that I'm doing right now in my lab as well as many others. And so we know that we have these tools that we can use to restore and to create resilient coral reef ecosystems. The thing that we need to do is do it at scale. We really need to start operationalizing these things. So while the situation is bad, I haven't lost all hope. There are still things that we can do," says Enoch.

Marine researcher Kyle Pisano says protecting the underwater ecosystem that maintains upwards of 25% of all marine species is not easy.

"Part of our mission here is to supply holding space for corals that need to escape from heat stress so they can come here. Another thing that all around the state, what we're doing is we're working on getting our in situ coral nurseries. Those are the coral nurseries that exist as structures out in the ocean on the bottom, the divers tend to. Kind of like, you see a lot of, like, CRF do that kind of work (Coral restoration Foundation). They're removing their nurseries or just building more nurseries into deeper areas to get them away from that hot water. That way that they don't get exposed to that extreme heat this year."

Last summer up and down the chain of islands that form the Florida Keys, coral rescue groups and government and academic institutions mobilized to save the coral from bleaching.

In mid-July 2023, water surface temperatures averaged about 91 degrees (33 Celsius) in the Atlantic off the lower Florida Keys, well above the average of 85 degrees (29.5 Celsius), according to National Oceanic and Atmospheric Administration reports.

The hot water resulted in nearly 100% bleaching along portions of the reef.

Scientific reports have long said loss of coral is one of the big tipping points of future warming as the world nears 1.5 degrees Celsius (2.7 degrees Fahrenheit) of warming since pre-industrial times.

That’s a limit that countries agreed to try to hold to in the 2015 Paris climate agreement.

“Oceans are incredibly important for humanity, for all the things they provide, and they deserve our attention to look after them and climate change is a substantial threat to all of those systems, so it's beholden upon all of us to take action on climate because it gives the planet the best possible future and hence all of us,” says Beeden.