Coral reefs are essential to ocean health, but dangerous coral bleaching is occurring more often and more widely due to warmer water, scientists report
Associated Press The Guardian 7 Jul 15;
Abnormally warm ocean temperatures are creating conditions that threaten to kill coral in the equatorial Pacific, north Pacific and western Atlantic oceans, the National Oceanic and Atmospheric Administration said on Monday.
Coral bleaching occurs when coral is stressed by changes in its environment, causing it to release algae living in its tissue. The coral then turns pale or white and becomes more susceptible to disease. In severe cases, it can die, permanently changing the habitat for fish and shellfish.
“The bleaching that started in June 2014 has been really bad for corals in the western Pacific,” said Mark Eakin, NOAA’s Coral Reef Watch coordinator, in a news release on Monday. “We are worried that bleaching will spread to the western Atlantic and again into Hawaii.”
The warmer oceans are a result of El Nino weather patterns and overall climate change, Eakin said. However, the frequency of these events indicate overall warming is more of a concern than individual weather patterns.
Eakin said in an interview on Monday that while El Nino weather patterns are in place, they developed well after this current event of coral bleaching began.
“We’re seeing an actual progression that goes along with this sort of big event, but it’s happening without a huge El Nino,” he said. “We’re seeing the more frequent return of these events primarily because the water temperature without an El Nino is already so warm it takes less ... to tip the scales and cause the corals to bleach.”
Global warming is affecting the oceans and “making the corals more susceptible”, he said.
Ocean temperatures, light and nutrient levels can cause bleaching. But NOAA says only warm temperatures can cause the widespread bleaching that scientists have been seeing since last year.
In 2014, Hawaii experienced widespread bleaching for the first time in nearly two decades. If it happens again this year, it would be the first time in history the Hawaiian Islands experienced consecutive years of bleaching, NOAA said.
Coral can recover from mild bleaching, but two consecutive years of bleaching could cause severe damage.
“Many healthy, resilient coral reefs can withstand bleaching as long as they have time to recover,” Eakin said. “However, when you have repeated bleaching on a reef in a short period of time, it’s very hard for the corals to recover and survive.”
In 2014, Kaneohe Bay on Oahu’s east side suffered the most serious bleaching in the state, which is home to 15% of all coral under US jurisdiction. Of the dominant coral species there, 75% lost some colour or turned completely white.
Coral reefs are a critical part of the ecosystem and their health is vital to the ocean environment. Coral covers just one-tenth of the ocean floor, but it is home to 25% of known marine species. Some fish eat coral, and others hide from predators in it. Some species use coral as nursery grounds and some types of shark frequent coral reefs.
15,000 sq km of coral reef could be lost in current mass bleaching, say scientists
Noaa predicts third-ever global bleaching event could cause a 6% global reduction in coral reefs in less than two years. More than a third of coral reefs affected may be destroyed forever
Karl Mathiesen The Guardian 7 Jul 15;
A massive coral bleaching event currently ravaging coral reefs across the globe could destroy thousands of square kilometres of coral cover forever, US government scientists have said.
In figures exclusively released to the Guardian, scientists from the US National Oceanic and Atmospheric Administration (Noaa) said about 12% of the world’s reefs have suffered bleaching in the last year. Just under half of these, an area of 12,000 sq km of coral, may be lost forever.
But the devastation is only getting started. The event could continue well into 2016. Noaa announced on Monday that the western Atlantic is about to heat up, turning the corals of the Caribbean bone white. When this occurs, bleaching will have hit every tropical ocean basin on Earth since June last year.
In all, scientists forecast a total of 15,000 sq km of reef may not recover and losses to the world’s remaining coral reefs would be a devastating 6%.
Dr Mark Eakin, the co-ordinator of Noaa’s Coral Reef Watch programme, said that given uncertainties around how long the event will continue it was very difficult to predict exactly how much reef would be wiped out.
“It probably won’t be as big as 1998, so we’re probably talking hopefully no more than 10%. Even if we’re talking one to 10% of the coral reefs around the world that’s a huge amount of coral reef area,” he said.
Global bleaching events have only been recorded twice before, in 1998 and 2010. Professor Ove Hoegh-Guldberg, director of the Global Change Institute at the University of Queensland, said Noaa’s figures, while rough, were decent estimates of the potential damage. He said, before 1998, bleaching of this magnitude had not occurred for “hundreds, if not thousands, of years”.
In 1998, a massive El Niño (an upwelling of warm water in the Pacific) set off a chain of warming events in oceans across the world that killed off 16-19% of the world’s coral reefs. Mark Eakin, the co-ordinator of Noaa’s Coral Reef Watch programme, said this year’s El Niño was playing a part, but “it’s almost certainly being driven largely by global warming”.
A huge patch of climate change-generated hot water, known as ‘the blob’, has been wobbling across the northern Pacific since this time last year. It first bathed the reefs of the Hawaii and the Marshall Islands in June 2014. It has now returned to where blitzed reefs have only just begun the slow process of rebuilding.
Other hot patches of water washed through the South Sea Islands during the southern Pacific summer. Reefs in the Indian Ocean were also hammered by warm temperatures.
“We are seeing real changes in the ocean as related to climate change,” said Eakin.
Corals can only tolerate a narrow range of temperatures. If the water around them warms by just 1C and this lasts more than a week, they are likely to bleach. After a mild warming event it is possible for polyps to regain their colour. But under extreme warming, the corals will die, meaning new colonies will have to grow.
“The recovery speed of these reefs, when you get a big bleaching event, is not a matter of a few years. It’s more on the scale of a decade or so,” said Eakin.
To establish the expected loss of coral from the current bleaching, Noaa used recent research from James Cook University, which found 40% of reefs in the Seychelles that were bleached in 1998 had now been replaced by weed and algae. Once this type of ‘regime change’ occurs, corals are unlikely to return.
Hoegh-Guldberg confirmed this “really high proportion” of lost corals was probably typical for massive bleaching events.
“The sorts of conditions we are facing are similar to 1998 and if it continues to develop we are going to lose coral again,” he said.
Hoegh-Guldberg said the background warming of climate change could also hamper recovery. After a warming event, corals that stayed stressed by even slightly warmer than normal temperatures recover more slowly.
“We’ve only had a 0.8C change in global temperature,” he said. “We’re already starting on a journey where just a mild change in temperature is causing a massive deduction in coral reefs. Just imagine when we get to 2C or 3C or 4C.”
In the Marshall Islands capital atoll of Majuro, where the Guardian observed massive bleaching last year, the first, fragile signs of a recovery have been found by scientist Karl Fellenius.
“Because the thermal event last July to December was severe, the coral colonies died right way. So the ‘bounce back’ would be new patches of coral on those clean skeletons, not recovery of those corals,” said Fellenius, who works on Majuro for the University of Hawaii Sea Grant programme.
“There are patches of new coral both on the lagoon side and ocean side of Majuro. Stuff is growing. But that’s like saying that 100 babies were born this year in the village, a ‘bounce back’ of sorts after 100,000 people died in a catastrophe last year,” he said.
But in dire news for the reefs in Majuro, and across much of the northern Pacific, the sea has begun to reheat.
“As of yesterday I see small patches of new bleaching on broccoli coral on the outer reef flat. That’s the first report [from the Marshall Islands] as far as I know,” said Fellenius.
Eakin said his models, which have predicted the passage of this event with remarkable accuracy, said the second wave of bleaching would also hit Hawaii and other Pacific island groups before moving into the Indian Ocean.
“This is two years in a row, and corals getting nailed in successive years like that are really going to take a beating,” he said.
This was the problem for corals worldwide as bleaching events piled one atop the other.
“The concern isn’t just about whether conditions are going to go back to normal, because we certainly expect they will. The question is how long does it take before they go back up to the really high temperatures that cause bleaching? That’s been coming much more frequently and in some areas its been getting much more intense,” he said.
There are stopgap measures that can greatly assist the chance of reef recovery for the time being. When a coral bleaches, it loses its ability to clean itself of algae. Once algae cover the surface, it is impossible for coral to repopulate. Herbivorous fish graze the coral and help keep it algae free. In polluted water, algae grow faster.
“Pollution and overfishing, if you’ve got a lot of that going on then coral reefs don’t recover very quickly. But if you can control those other factors you can improve the ability of corals to bounce back,” said Hoegh-Guldberg. Fellenius said he had asked the Marshall Islands government to enact temporary fishing closures during bleaching episodes.
But Hoegh-Guldberg, who in 1999 predicted the loss of most of the world’s coral reefs by the middle of this century, said the only hope for coral reefs to survive long term was rapid curbing of carbon emissions to stop the world from warming more than 2C.
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