Claim: Major discovery helps explain coral bleaching


Research News


Corals, like all animals, must eat to live. The problem is that most corals grow in tropical waters that are poor in nutrients, sort of like ocean deserts; it’s this lack of nutrients that makes the water around coral reefs so crystal clear. Because food is not readily available, corals have developed a remarkable feeding mechanism that involves a symbiotic relationship with single-celled algae. These algae grow inside the corals, using the coral tissue as shelter and absorbing the CO2 that the corals produce. In exchange, the algae provide corals with nutrients they produce through photosynthesis. These algae contain a variety of pigments, which give the coral reefs the colors they’re known for.

Over the past 35 years, tropical oceans have experienced multiple major heat waves. Scientists have observed that during these episodes, the algae – stressed by the warmer temperatures – release compounds that are toxic to the coral, prompting the coral to expel the algae from their tissue. That means the corals lose their color and their primary food source, and then begin to starve. This is the process of coral bleaching. And it has been occurring more and more frequently, threatening the survival of many reefs, including Australia’s Great Barrier Reef. Bleached corals do not necessarily die; their symbiotic algae population can be reestablished if the conditions around a reef return to normal. But if the heat persists, or is aggravated by other factors like pollution, the coral becomes too weak to survive.

In a paper published in the prestigious PNAS on 25 January, an international team of scientists that includes Nils Rädecker at EPFL’s Laboratory for Biological Geochemistry (LGB), reveals a major discovery related to how the symbiotic relationship ends between the coral and algae. “We showed for the first time that the coral starts to suffer from hunger long before the algae are expelled. The algae apparently stop providing sufficient nutrients while they are still inside the coral tissue,” he says.

When symbiosis no longer works

Scientists already knew that ocean warming is the main factor causing the symbiotic relationship to break down. But what Rädecker’s team discovered was that the coral is already in a stressed state and lacking nutrients even before the algae begin releasing toxic compounds. “The roots of the problem are much deeper than we thought, and they involve an early breakdown of the metabolic exchanges in these fascinating organisms,” says Anders Meibom, the head of LGB and a world-renowned coral expert.

Rädecker spent more than a year studying a coral reef just off the coast of Thuwal, Saudi Arabia – the city where the Red Sea Research Center, part of the King Abdullah University of Science and Technology, is located. He then replicated these environmental conditions in the aquaria at the Center so that he could investigate the corals under controlled conditions. The data were then analyzed at several laboratories, including EPFL and the Biology Department at the University of Konstanz in Germany.

Calling known facts into question

“Based on what we found, we can determine which environmental conditions other than temperature (such as water quality) stress the corals in a reef, and use this information to predict whether the reef will bleach. Our findings can also be used to identify corals that are particularly resistant to bleaching, like those in the Gulf of Aqaba and elsewhere in the Red Sea. That will tell scientists which reefs should be protected because they have a better chance of survival,” says Rädecker.

According to Meibom, this study makes a major contribution to coral research and sheds new light on earlier observations. “Nils’ research has uncovered metabolic mechanisms that play a fundamental role in the coral bleaching process – and that we didn’t understand the importance of until now. I believe he found the key to what’s actually going on inside corals when they’re stressed by global warming,” he says.


From EurekAlert!

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January 26, 2021 2:12 am

Lower water levels mean the sea water is flowing away from the area. as well as increasing the exposure to direct sunlight.

Hence there is no incoming flow of nutrients.

I have mentioned this before.

Richard Page
January 26, 2021 3:21 am

Is it me or does the ‘Global Warming dun it’ rhetoric sound a bit half-hearted in this study? Almost as if they know they’re peddling a lie but have to go through the motions anyway.

Reply to  Richard Page
January 26, 2021 4:10 am

Been going on in climate research for a while, as when the church was all powerful and nobody could contradict the dogma, but did anyway in code.

Reply to  Richard Page
January 26, 2021 8:16 am

I thought the ocean water temps have only gone up like 0.1 C if that. Are algae really that sensitive to temps? If so why didn’t corals die off in the warmer early holocene?

Or more likely this just sensitivity to normal localized warmth extremes that have always occurred to some degree.

Reminds me of the ozone hole. When you start to study something new and find something unexpected, the knee-jerk reaction seems to be “wow maybe something humans did is causing that”. Nobody thinks “well maybe this has always been occurring”. But I suppose that’s too boring and doesn’t “sell the papers”.

That’s the problem with science today, you always have to gin up a crisis to get name recognition in their little community.

Reply to  menace
January 26, 2021 12:10 pm

Closer to 0.01C.

Reply to  menace
January 26, 2021 1:11 pm

Humans from earliest babyhood seek to control their environment – any parent knows this. The wish for control translates into assuming causal links between action and result. This means it is much easier to get people to believe that their (or others’) actions are causal than to persuade people of how little control they have. The problem is particularly acute in relation to statistical and natural phenomena, where we humans have histories over hundreds of thousands of years of doing things that are supposed to control them such as the proverbial rain dance or crossed fingers. This is also one very powerful attraction of religions to believe in some entity that can help in establishing control.

Given this human propensity, rational arguements are probably doomed. At least this is how I feel after a bad night.

January 26, 2021 4:43 am

Some folks are claiming that coral bleaching is an increasing problem. Some other folks point out that claimed bleaching events are exaggerated. Apparently some of the alarmists have engaged in much academic misconduct.

Do we have a source we trust that outlines the extent of coral bleaching and whether the problem is actually increasing or not?

Reply to  commieBob
January 26, 2021 4:52 am

The biggest problem might be that gazillions are being pumped into dorks “researching climate change disasters” while nobody spends much money proving otherwise. As for academic misconduct, you may be holding the sciencers* to the wrong standard.
*Sciencery: The practice of research to prove whatever the client pays for. For a fee, a sciencer can make any product or service walk on a cloud of scienciness.

Reply to  paranoid goy
January 26, 2021 8:11 am

Remember those 1960s tv ads for toothpaste or cigarettes that started with a dude in a white coat saying – “scientists say (blah blah blah)?

What’s changed?
(except now it’s governments that spruik their snakeoil by intoning the “scientists say” mantra)

Reply to  Mr.
January 26, 2021 9:02 am

Yeah, just so you know, I saw my first television in 1979. Our government was quite adamant that we will “never have those devilish things”, until then. Even Nigeria had TV before us, and we were the “most advanced country on the continent”! We had atom bombs, fer fuxaches!

Peta of Newark
January 26, 2021 5:06 am

“”Over the past 35 years, tropical oceans have experienced multiple major heat waves“”

We all know that is Complete Junk from the get-go.
Only the sun can warm the ocean

David A
Reply to  Peta of Newark
January 26, 2021 7:23 am

I think he means water T. And it is true either way over the last 35 years, 350 years. 3,500 years. 35,000 years etc…

January 26, 2021 5:08 am

Sorry for ot:
Scientists spot 6 alien worlds orbiting a star in strange — but precise — harmony
“Astronomers poring through data from NASA’s Transiting Exoplanet Survey Satellite (TESS) discovered three planets around a star dubbed TOI-178 (TOI stands for TESS Object of Interest). And when scientists looked at these observations more closely, they realized that the worlds seemed to be keeping time against each other. So they recruited some more instruments — and discovered the system hosts at least six planets, five of which tick off orbits in rhythm with the others. And unlike those of other synchronized systems, the planets are an unusually mixed bag.”

Artists view of the system, sound must be “on”

John Shotsky
January 26, 2021 5:56 am

Corals have been around far longer than humans. They’ve survived ice ages, and sea level changes of hundreds of feet. Just 12000 years ago, the sea level increased about 500 feet. As soon as the report mentioned warmer water as the ‘trigger’ for coral bleaching, without even a mention of all the pollutants we are introducing to the oceans, my eyes glazed over.
Where is the study that shows that the oceans in coral growth areas are actually warming?

John Tillman
Reply to  John Shotsky
January 27, 2021 2:38 pm

Suntan lotion from environmentalist divers is a far greater threat to corals than CO2.

David Roger Wells
January 26, 2021 6:06 am

Fake Invisible Catastrophes and Threats of Doom Patrick Moore. Read the book it successfully debunks all of the nonsense about coral and bleaching and much more. The problem is that climate and environment is sort of complicated which is why the simplicity of Co2 is a pollutant gets so much leverage. Biden is no intellect and a clip I saw was him sitting with a pile of executive orders to sign a mile high. Biden is not in charge he exists merely to fulfil the beliefs of those similarly compromised by beliefs by signing executive orders and impose legislation based upon belief.

That is why the environment will suffer and those who recognised the duplicity need to work harder to increase understanding.

January 26, 2021 7:23 am

I see these researchers are making the assumption that there is only one breed of symbiont for every type of coral.
Actual scientists know that there are a large number of potential symbionts and that the temperature of the water determines which one the coral will prefer.
What is happening is that the coral is expelling one symbiont, in favor of a different one that is better suited to the new conditions.

Reply to  MarkW
January 26, 2021 8:28 am

Scientists would be better suited to help coral by studying the symbionts and “helping” the coral get more suitible symbionts established when they start to bleach out.

Also they could potentially study genes of symbionts and use gene splicing to improve the compatibility so that more stress can be tolerated before rejection.

This would be the sort of science that would impress me.

Reply to  menace
January 26, 2021 12:20 pm

Corals survived the last few million years without help.

John Tillman
Reply to  Mike Jonas
January 27, 2021 2:42 pm

Corals date from the Cambrian Period, c. 535 million years ago (Ma).

Modern stony corals arose in the Middle Triassic, ie about 240 Ma. If anything, they like it hot, but can obviously thrive under the much colder conditions of the past 34 million years.

Alan Robertson
Reply to  MarkW
January 26, 2021 8:48 am

There are interesting parallels in this story, between corals and human political rhetoric.

Whites, having stripped the environment of resources, must then live via their exploitation of the coloreds. They expel their established underlings when they begin to profit too much and get uppity, setting up the next round of importation of a whole new color to exploit.

LOL@Klimate Katastrophe Kooks
Reply to  Alan Robertson
January 26, 2021 9:41 am

If you believe that’s what’s taking place today, you’re discounting the fact that we fought a war to get away from Britain (which imposed slavery upon the colonies), we fought another war to free the slaves (said war against democrats… the democrat party was started for the express purpose of expanding slavery into the Kansas-Nebraska territories, whereas the Republican party was started by anti-slavery activists for the express purpose of ending slavery), we fought against democrats who refused women’s suffrage for 40 years until Republicans finally got a majority and pushed it through, we fought against democrats who opposed de-segregation and equal rights, and today we fight against democrats who keep minorities living in slums, giving them free stuff in return for their votes (and that vote is expected and viciously enforced… people have been forcibly taken to the polls, beaten up and even killed if they refused to vote democrat)… but who wants to bet that Alan Robertson here is a democrat because he’s a typical low-information individual who just swallows any shite-sandwich the higher-education indoctrination centers cram down his throat, never once stopping to research history for himself.

What makes America unique isn’t that we had slavery… slavery was ubiquitous throughout the world in those days (and still is in many places). No, what makes America unique is that we put in place an economic system which wasn’t predicated upon exploiting people for their labor and instead allowed people to prosper by serving their fellow man (ie: capitalism), and we put in place a political system which guaranteed certain fundamental rights such that capitalism was protected and allowed to flourish so anyone willing to work at serving their fellow man could prosper.

But who wants to bet that Alan Robertson here is at least a liberal, and most likely a socialist or communist, because he’s a typical low-information individual who just swallows any shite-sandwich the higher-education indoctrination centers cram down his throat, never once stopping to research history for himself.

Well, Alan, you’re about to reap what you’ve sown… perhaps if you buckle down and study history now, you can avoid the inevitable starvation, but I’m betting you’ll double-down on your deluded belief in the economic and political system of liberalism / socialism / communism / Marxism / nazism (all offshoots of that malevolent ideology known as collectivism) which has killed more than 120 million people just in the past century alone. And if that is the case, you deserve what you’re about to get.

Alan Robertson
Reply to  LOL@Klimate Katastrophe Kooks
January 29, 2021 8:49 am

Thanks for responding.
If I knew how to edit my posts, I would have done so immediately, after posting in haste, while distracted.That’s where the confusion begins. My post was incomplete and appeared to many, to say something other than my intent.
However, if one looks closely enough at what I actually said, the intent should still be clear.

“…I’m betting you’ll double-down on your deluded belief in the economic and political system of liberalism / socialism / communism / Marxism / nazism…”

You couldn’t be more wrong about what I said, or what I believe. Although I’ve been an infrequent visitor here of late, I have sufficient histroy at WUWT that long time participants can tell you that your assessment is grossly mistaken.

I was attempting to mock the political rhetoric of just those spokesmen for the ideologues you mentioned.
My purpose was to show a similarity between how corals respond with their symbionts in the real world, vs. unreal modern political rhetoric in the unreal world created by the media blaming everything they can on racist white bigots who turn their back on science in order to keep all the people of color down.

Even had the reader misinterpreted what I’d originally stated, (there is a certain amount of reading comprehension required,) all follow up posts should have given enough insight into what I’d attempted, however incomplete my attempt.

Ps If anyone out there would like to instruct me about how to edit our posts, I’d gladly accept the help.
note: I won’t go back at this late hour and edit anything I’ve said in this thread, leaving it all, for context..

Alan Robertson
Reply to  Alan Robertson
January 26, 2021 11:30 am

By the down votes, I’m guessing that some here must not have noticed the recent plethora of the sort of political rhetoric I described, or the article in these very pages, detailing how Joe Biden’s “Senior Director for Climate Justice”, Dr. Cecelia Martinez has attributed climate change to “systemic racism”.

Perhaps those people simply jumped to conclusions and attributed an endorsement of such sentiment, to me.

I invite those people to demonstrate that they have a set and make their own comment as to why they disagree with what I’ve pointed out to be true, in political speech.

Ps There is also the view that the down voters know what I said is true and endorse such policies, thus keeping with their own goals of not only suppression of speech of those who disagree with them, but also of anyone pointing out what they are actually doing.

Reply to  Alan Robertson
January 26, 2021 3:51 pm

It would have helped if you added a sarc tag or put the sentence in quotes and mentioned the wacko that actual said it.

Alan Robertson
Reply to  PCman999
January 26, 2021 5:25 pm

Thanks for taking the time to write about your understanding of the comment.
I’m not the most articulate person and could certainly have made a better effort to get my point across.
At the time, I thought it would be obvious, but now see how it is not.

Reply to  Alan Robertson
January 26, 2021 12:13 pm

I sure hope that was sarcasm.

Alan Robertson
Reply to  MarkW
January 26, 2021 12:30 pm

I take it that you are referring to my first comment.
I hope that my follow up comment helped clarify what I was trying to say.
It’s possible that people simply didn’t like the way I spoke in the first comment.
Oh well.

Also, much that we observe in the living world, we find in ourselves.
There’s a reason for that.

To bed B
Reply to  Alan Robertson
January 26, 2021 2:28 pm

Your first comment read like an endorsement of such views.

Alan Robertson
Reply to  To bed B
January 26, 2021 3:25 pm

Thanks for your comment.

Reply to  Alan Robertson
January 26, 2021 3:56 pm

Climate Alarmists and the Climate Emergency they fabricated are racist – Rich white neo-nazis don’t care about carbon taxes and Rube Goldberg renewable energy schemes that drastically increase the cost of energy. Everyone else, whatever the shade of melanin they have, don’t want to waste money on that and would rather feed their kids and pay the bills.

Alan Robertson
Reply to  PCman999
January 26, 2021 5:17 pm

Almost all political rhetoric concerning climate change, is designed to create acceptance by the populace, of whatever measures the controlling elites envision. The problem becomes, what is the real goal of such efforts by the elites?

We have seen many quotes, by such people as Ted Turner, preaching the idea that too many human beings exist and populations must be reduced, by whatever means necessary. Consider Bill Gates’ geoengineering effort to dim the Sun’s rays reaching Earth. He has no lack of willing followers, convinced that they are right, because they want to save the planet, after all. There is a very great likelihood that world wide harvests would be greatly reduced, with mass starvation as a result. One need only examine the rhetoric of Mr. Gates in other contexts, to decide for yourself, if that is actually his goal.

The widespread success that the climate fearmongers have achieved, in spreading their climate indoctrination, spells trouble for the rest of us.
It wasn’t a fluke that such people as Jim Jones and Marshall Applewhite were able to trick their followers into mass suicide.
All they needed to do was convince their followers of their separateness from “the others” and the superiority of their goals, in some righteous endeavor.

Consider how major political figures in the US, constantly fan the flames of division and hatred between all of us, for differences in shades of color.
Assure that the vilification of those with differences, penetrates deeply into society and just as history shows, there is no end to the horrors that men will inflict upon each other.
Apply the techniques perfected by such as Beria and Goebbels, to climate scares, et voila! “How dare you”.

Rick C
Reply to  MarkW
January 26, 2021 1:49 pm

Yes, Jim Steele wrote an excellent essay on this that was posted here a while ago. It’s also the reason experiments in aquariums which lack the spores (seeds, larvae?) of many algae species result in dead corals while in the real word bleached corals recruit new symbiots and recover relatively quickly.

Reply to  Rick C
January 26, 2021 2:14 pm

I studied marine biology at University and saw for myself the fish tank / aquarium experiments to try to assess behaviour or survival of small organisms like crustaceans. Invariably they were an abject failure – organisms under study quickly died. Making a fish tank, however big and elaborate, representative of the real ocean, is a hopeless endeavour.

Gordon A. Dressler
January 26, 2021 7:50 am

Hmmm . . . absolutely no mention of ocean “acidification” causing coral bleaching.

Amazing thing, that!

January 26, 2021 8:21 am

“Scientists already knew that ocean warming is the main factor causing the symbiotic relationship to break down.”

Hmm, I thought scientists “already knew” that ocean “acidification” due to CO2 uptake was the cause of bleaching not the sea temperatures.

Always take “scientists already know…” with a grain of salt.

Richard Page
Reply to  menace
January 26, 2021 8:33 am

Scientists already know quite a lot of things actually. Understanding them has always been the problem.

Weylan R McAnally
Reply to  Richard Page
January 26, 2021 11:44 am

1500 years ago, everybody “knew” that the earth was the center of the universe. 500 years ago, everybody “knew” that the earth was flat. And 15 minutes ago, you “knew” that humans were alone on this planet. Imagine what you’ll “know” tomorrow. – Agent K, Men In Black

Peter W
Reply to  Weylan R McAnally
January 26, 2021 12:41 pm

100 years ago everybody knew that the continents were fixed in position and were incapable of drifting around across the face of the earth.

John Tillman
Reply to  Peter W
January 27, 2021 2:48 pm

Less time ago than that. Even in 1950, that was still the consensus. Then seafloor spreading was discovered by the US Navy.

John Tillman
Reply to  Weylan R McAnally
January 27, 2021 2:47 pm

Greek scientists knew that the Earth was basically spheroidal since about 600 BC. Even the Early Church Fathers who defended the biblical flat Earth until around AD 400 were replaced by Christians who accepted a spherical Earth, but at the center of the universe, or slightly off center, but with other spheres orbiting it in perfect circles. Wrong, but less wrong.

January 26, 2021 8:55 am

Over the past 35 years, tropical oceans have experienced multiple major heat waves.”
What a stupid and deliberately vague statement.
Do they mean that heat waves took place in the last 35 years for the first time in the earth’s 4 billion year history? That sea water never before reached such temperatures?
Is anyone out there stupid enough to believe Mike Mann’s hokey stick?
An identical frequency and intensity of heat waves probably happened in the 1930’s-40’s.
And in previous centuries also.

What would it cost them to be honest and just start with:
“Tropical oceans periodically experience major heat waves.”

LOL@Klimate Katastrophe Kooks
January 26, 2021 9:23 am

They make it sound as though the coral expels the algae, and only after conditions return to normal does that same algae return to the coral… in reality, the coral expels the algae so that more-fit algae can take up residence. Coral bleaching is akin to evolution via a different mechanism… rather than the organism evolving to become more-fit, the coral simply replaces the less-fit organism with a more-fit organism. Thus, bleaching makes the coral more-fit for the current circumstances.

Thus coral can rapidly adapt to changing conditions… if this were not so, coral would have died out long ago. The changes the coral sees today are nothing in historical comparison.

Paul Johnson
January 26, 2021 9:38 am

This research suggests there are often long-standing resource-sharing issues in the coral-algae relationship, but that unrelated outside factors can trigger the actual expulsion of the live-in partner. The coral then becomes highly needy and vulnerable until a new symbiont already present in the environment is recognized as an opportunity for a more supportive relationship.

This scenario can be confirmed by any number of Hallmark Channel movies.

January 26, 2021 2:18 pm

Why are they blathering on about heating of water? Jim Steele has shown conclusively that many coral bleaching episodes result from the precise opposite – cooling and sea level fall, exposing corals above the water line.

No mention of cooling and coral exposure in this diatribe means it’s fiction, likely that no-one involved went anywhere near a coral reef.

January 26, 2021 6:44 pm

Scientists already knew that ocean warming is the main factor causing the symbiotic relationship to break down.”

Assumptions are not facts.

This smacks of confirmation bias with the warning sign: HE THEN REPLICATED THESE ENVIRONMENTAL CONDITIONS IN THE AQUARIA”.

Salt water aquariums are not simple environments!
First they must prove their aquariums are not negative influences!

January 26, 2021 8:09 pm

This seems like half an article.

January 26, 2021 9:21 pm


From Wiki: The Great Barrier Reef runs ~1400mi, not far from a North to South direction and roughly Lat 10-30 degree S.
My questions: What is the typical sea temperature difference from north to south along the GBR? Is this gradient more or less than the temperature increase that is purported to have caused the bleaching?
Seems to me an algae symbiont that tolerates warmer(colder) water would inhabit more northern(southern) regions, thus naturally restoring any coral bleaching from changing sea temperatures. Humans just need to avoid over fishing, crop run-off and pollution to “save” the coral reefs.

John Tillman
Reply to  Bill Zipperer
January 27, 2021 2:49 pm

Don’t use sunblock if you’re diving!

January 27, 2021 2:16 am

Most of the vast area of the worlds oceans are saline deserts . only about 4-5 % of ocean is actually productive .Life cannot survive in these huge sterile areas , there is just not enough nutrients specifically PROTEIN !!!! What sea life needs to prosper is food and something to fasten to near the surface . The average depth of the Pacific ocean is 12,000 feet.
Sea life needs protein and other nutrients to survive and thrive . Man could vastly increase the seafood harvest from the worlds oceans if we just feed them ! We waste vast amounts of the necessary nutrients , fats and protein in sewage treatment plants near the coast all around the earth . These sewage flows should instead be pulverized , ground up to a liquid state and pumped out to sea into deep water . In those areas would be seen a vast increase in marine life and fish . If pumped out far enough there would be no worry of polluting the area and dangerous bacteria would be destroyed by other more populous good bacteria. In addition if large areas of ocean were covered with floating pontoons with chains hanging beneath a huge new marine life environment would grow rapidly along with fish stocks feeding off of them .

January 27, 2021 9:40 pm

A recent (peer-reviewed) article found that coral bleaching had been occurring throughout the entire period of their 400 year study. 
[“Reconstructing Four Centuries of Temperature-Induced Coral Bleaching on the Great Barrier Reef Nicholas A. Kamenos and Sebastian J. Hennige” 
Front. Mar. Sci., 15 August 2018 | %5D   

Additionally, from my site’s The Commentary
“As it is mainly the relatively untouched northern areas of the GBR affected, it is unlikely that run-off is the cause. The current bleaching decreases towards the south, flowing on the north-to-south counter-clockwise current from Vanuatu, along southern PNG, then south along the Queensland coast, and becoming depleted in the process. Upstream undersea volcanic activity around Vanuatu produces toxic H2S (Chapter 4a, Cyclone Pam), in time oxidising to sulphuric acid, lowering pH, but less toxic at that level. Chapter 5 shows the small acidity produced by CO2 is not a concern.

Other coral bleaching areas around the globe, eg Seychelles, Caribbean, Maldives, etc are downstream from undersea volcanic areas. However, Persian Gulf corals are not influenced by undersea volcanic areas and are not bleached, despite being 36°C – much higher than the GBR’s 32°C encountered preceding bleaching events.”

January 28, 2021 12:47 am

So, let me get this straight, corals, which evolved in the Cambrian era, when temperatures were 7C higher than today and CO2 in the atmosphere was at levels of 7 to 10 times todays, are sensitive to global warming of 1C. Does that make sense to anyone?

Alfred (Cairns)
January 28, 2021 12:28 pm

The obligatory phrase “Global Warming”. But the earth has been entering a cooling cycle for 10 years now – hence the introduction of the phrase “Climate Change”

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