More Evidence for Rapid Coral Adaptation

By Jim Steele

Good news continues to accumulate regards corals’ ability to rapidly adjust to changing climates. The view of coral resilience has been dominated by the narrative of a few scientists. In the 1990s they advocated devastating consequences for coral reefs due to global warming, arguing coral cannot adapt quickly enough. Since the Little Ice Age ended, they believed rising ocean temperatures had brought coral closer to a “bleaching threshold”, a more or less fixed upper temperature limit above which corals cannot survive. Their model predicted the speed of recent global warming “spells catastrophe for tropical marine ecosystems everywhere”. Their assertions that “as much as 95% of the world’s coral may be in danger of being lost by mid-century” was guaranteed to capture headlines and instill public fear. However, a growing body of scientific research increasingly casts doubts on such alarming predictions. Unfortunately, that good news gets much less attention.

A recent peer-reviewed paper titled A Global Analysis of Coral Bleaching Over the Past Two Decades (Sully 2019) compared 20 years of ocean temperatures at which coral bleaching was initiated. From 1998 to 2006, the average sea surface temperature that initiated bleaching was 82.6 °F. But that temperature limit proves not to be “fixed” as earlier researchers incorrectly believed. From 2007 to 2017 the average temperature limit that initiated bleaching was higher, 83.7 °F. This indicates coral have been rapidly adapting to warmer regional climates much faster than once believed.

Based on these new observations the scientists concluded, “past bleaching events may have culled the thermally susceptible individuals, resulting in a recent adjustment of the remaining coral populations to higher thresholds of bleaching temperatures.” Furthermore, they suggested, “Localities that commonly experience large daily, weekly, or seasonal SST ranges [Sea Surface Temperature] may harbor corals, and strains of coral symbionts, that are more resistant to SST extremes.”

Other studies also observed similar rapid adaptations. Studies in Indonesian waters determined that two coral species, both highly susceptible to bleaching, had experienced 94% and 87% colony deaths during the 1998 El Nino. Yet those same species were among the least susceptible to bleaching in the 2010 El Nino despite a similar increase in water temperatures with only 5% and 12% colony deaths.

In the context of coral evolution over thousands and millions of years, such rapid adaptation was suspected by many scientists. After all, none of the coral reefs we observe today, that depend on symbiotic algae, existed 18,000 years ago. The last Ice Age Maximum lowered sea level by 400 feet, killing all coral above those depths. As ice sheets melted, oceans warmed, sea levels rose, and coral rapidly adapted to those ever-changing conditions. More recently, estimates of ocean temperatures just 3000 to 5000 years ago range from 1.8°F to 9°F warmer than today. And clearly those warmer temperatures did not result in massive coral extirpations, thus casting further doubt on predictions of massive coral deaths by 2050. Evidence of bleaching thousands of years ago also reveals it is not just a recent phenomenon.

Studies of coral reefs that existed thousands and millions of years ago, find the lowest extinction rates occurred in the warmest tropics. Sully 2019 similarly found “coral bleaching was less common in the equatorial regions.” In contrast to earlier “models that predict minimal coral survival in the tropical oceans within the next 100 years, recent field work shows considerable geographic variability in both temperature stress and coral survival”. Thus, they argue there is an “urgent need to develop better models” to more accurately predict coral bleaching.

Sully 2019 hypothesized “localities that commonly experience large daily, weekly, or seasonal SST ranges may harbor corals, and strains of coral symbionts [symbiotic partners], that are more resistant to SST extremes.” Increased resilience to a variety of bleaching events, whether induced by anomalous warmth or cold, prompted the Adaptive Bleaching Hypothesis first proposed in 1993. That hypothesis suggests that although bleaching events are a response to stress, by ejecting susceptible symbionts, coral create the potential to acquire totally new and different symbiotic partners that are better suited to new stressful conditions.  A broader analysis of the Adaptive Bleaching Hypothesis is discussed in the article “The Coral Bleaching Debate: Is Bleaching the Legacy of a Marvelous Adaptation Mechanism or A Prelude to Extirpation?

Because coral live in nutrient depleted environments, many species require single-celled photosynthesizing symbionts that typically provide ~90% of the coral’s energy needs. Just 40 years ago it was believed all corals were host to just one photosynthesizing symbiont. But thanks to technological advances in genetic sequencing, we now know a coral species can harbor several potential symbionts, each capable of responding optimally to a different set of environmental conditions. As predicted by the adaptive bleaching hypothesis, genetic techniques have now revealed a wondrously diverse community of symbionts with which coral can partner.

The more alarmist researchers had argued coral can only adapt very slowly over thousands of years via genetic mutation and natural selection. They incorrectly believed coral’s upper temperature limit is “fixed” for decades and centuries. But corals are now seen as an “eco-species” that can rapidly evolve and adapt to changing climates by expelling and acquiring new symbionts. Various symbionts enable various temperature tolerances.

To summarize Sully 2019, they found:

1. Coral now require higher ocean temperatures to bleach than the temperatures that caused bleaching a decade ago. This suggests rapid coral adaptation.

2. Coral bleaching was significantly lower in localities with a high variance in temperature anomalies. Localities with high variability likely maintain a wide variety of symbionts and coral genotypes.

3. There has been no universal response to global warming. Despite similar changes in temperature, bleaching was much less likely in equatorial region where coral diversity was highest.

4. Rapid changes in temperature can result in more bleaching, but the causes of rapid temperature change, such as an El Nino, were not analyzed.

Unfortunately, the last sentence in Sully 2019, reveals how some editors and journals are politicizing the science, and downplaying any optimism. Sully 2019’s last sentence read “immediate action globally to reduce carbon emissions is necessary to avoid further declines of coral reefs.” But Sully 2019’s research never tested or analyzed the effects of CO2 on temperature and bleaching. Their research only revealed resilience and rapid adaptation to warming, whether that warming was natural or CO2 induced. Furthermore, their research reported susceptibility to bleaching varied over time and location and did not detect a CO2 fingerprint. Their research did not determine whether rapid changes in regional ocean temperature were caused by changes in El Nino, shifting ocean currents, changes in upwelling, cloud cover or CO2 concentrations. In the past, honest and objective scientific journals restricted comments to conclusions based on the author’s actual research.

Over the years I have had several researchers thank me for posting information in my blogs that their editors had not allowed. They tell me editors have insisted on more catastrophic CO2-biased conclusions in order for them to publish. We also know from published emails that alarmist scientists like Michael Mann and Kevin Trenberth have actively “persuaded” journal editors, via bullying or other means, to obstruct publication of any skeptical scientific research that undermines Mann’s and Trenberth’s dire predictions. Sully’s CO2-alarmist, non-sequitur closing sentence is most certainly the fingerprint of another such enforced distortion that is now being superimposed on otherwise objective science.

Jim Steele is retired director of the Sierra Nevada Field Campus, San Francisco State University

and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism

0 0 votes
Article Rating
Newest Most Voted
Inline Feedbacks
View all comments
April 2, 2019 8:59 pm

If you have an interest in this area of research you may want to read some of the papers by Paul Kench available without paywalls on

Also if you are on researchgate yourself you may want to “follow” Paul. He is a breath of fresh air. A high level scientist with not a single climate activism bone in his body.

ferd berple
Reply to  Chaamjamal
April 3, 2019 9:16 am

Name one place on earth where the ocean is too warm for coral to grow. You can’t. The Red Sea, with the warmest ocean temperatures has some of the most spectacular corals on earth.

Coral reef are rare outside the tropics. They are almost universal in the tropics.

Anyone that suggests warming is a threat to corals has not done their homework.

Dr Bob
Reply to  ferd berple
April 3, 2019 3:19 pm

Coral ‘bleaching’ in the northern sector of the GBR is directly related to extended periods of high atmospheric pressure during the SH Summer. The presence of slow-moving high pressure cells and stationary high pressure ridges cause a drop in sea level, cloudless skies and dead calm seas; doldrum-like conditions prevail.

Under these natural weather conditions, corals in these pristine, very transparent, relatively shallow seas are exposed to extremely high levels of UV solar radiation. UV radiation levels in the Tropics are harmful to humans after even relatively short periods of exposure (20 minutes without suitable protection).

In the case of corals, coral bleaching (evacuation) occurs to escape ‘sunburn’; it seems unlikely that SST’s, except in extremely shallow seawater (an inch or two?), play any significant part in this reaction to UVR exposure.

The following observations were published in ‘Effects of ultraviolet radiation on corals and other coral reef organisms’ (Shick, Lesser & Jokiel, in Global Change Biology (1996) 2, 527-545.

‘The discovery of the importance of solar ultraviolet radiation (UVR) as a factor affecting the biology of coral reefs dates only to about 1980.’

‘The high transparency of tropical ocean waters allows UVR to penetrate to depths of 20 metres (65 feet) or more (Gerlov 1950; Smith & Baker 1979; Fleischman 1989; Gleason & Wellington 1993).’

‘MacMunn (1903), in discussing the pigments in azooxanthellate (non-symbiotic) dendrophylliid corals, was apparently the first to state that UVR is potentially damaging to corals.’

‘Catala-Stucki (1959) subsequently noted that most corals suffer when exposed to high doses of artificial UVR which, if prolonged, may be fatal.’

‘ Jokiel (1980) demonstrated that cryptic reef epifauna were killed by acute exposure to solar UVR in shallow water and suggested that the structure of coral reefs was affected by the relative UV tolerances of their constituent species.’

‘Harriott (1985) suggested that the mass bleaching of corals on the Great Barrier Reef during the warmest part of the year was caused in part by increased penetration of UVR, because bleaching occurred only on the upper and unshaded surfaces of colonies and extended to deep colonies only in very clear water. Similar reasoning was offered by Fisk & Done (1985) to explain bleaching elsewhere on the GBR, and by Goenaga et ai. (1989) for bleaching in the Caribbean.’

The recent coral bleaching events on the Northern GBR coincided with extensive die-back of mangroves around the southern coastline of the adjacent Gulf of Carpentaria; this die-back was, no doubt, caused by the drop in sea level which occurs under the influence of high atmospheric pressure.

April 2, 2019 9:01 pm

I hope someone forwards this to the judge in Australia who had Peter Ridd’s case…

Reply to  BobM
April 2, 2019 9:25 pm

If you have the judge’s address, I would gladly defend Peter Ride and forward this analysis!

Reply to  Jim Steele
April 2, 2019 9:54 pm
Reply to  Jim Steele
April 2, 2019 9:56 pm

Actually, you could talk to Peter’s lawyer about whether you can submit an amicus curiae brief. Talking to the judge directly may be a no no.

Reply to  commieBob
April 2, 2019 10:21 pm

Yes I think the judge can only now consider materials presented as evidence during the course of the court appearances.

Reply to  Mr.
April 2, 2019 10:51 pm

Has anyone asked Sully why he included the CO2 disclaimer?

I think it’d be interesting to hear in his words why he felt it necessary..

Reply to  commieBob
April 3, 2019 2:05 am

Speaking to Ridd’s lawyer would be a smart first move. More likely that an unsolicited input would have a counter effect, whether or not is can legally be considered. I’m sure he has lots of unwanted mail on this subject.

Komrade Kuma
Reply to  Greg
April 3, 2019 2:29 am

An unsolicited approach would just be a free hit to the green blob apparatchiks and their media acolytes/brown nosers. Go to the lawyer. Ridd can provide all the expert assessment the lawyer will require. It would come in as expert evidence as distinct from evidence of fact.

Reply to  Jim Steele
April 3, 2019 10:55 am

Submit the evidence instead to the research funding officers of JCU.

Charles Higley
Reply to  BobM
April 3, 2019 5:01 am

Few people wear the same clothes every day all year round regardless of the temperature or the season. Corals are just as sophisticated as us.

Gerry, England
Reply to  BobM
April 3, 2019 5:48 am

I am not sure it would be relevant since the tribunal is about which is superior – the code of practice or the employment contract. That the judge noted the difference between the effort – and possible legality of it – to prove a breech of the code of practice and the lack of interest in the quality control problem may be a decider.

ferd berple
Reply to  Gerry, England
April 3, 2019 9:27 am

In law, the specific has precedent over the general. For example, you shall not kill is the general case, except in self defence is the specific case.

I would expect the employment contract is specific while the code of conduct is general.

The problem is the age old “a slave cannot have two masters”. If a slave receives two different orders from two different masters, how can the slave be expected to satisfy both?

April 2, 2019 9:32 pm

The dude abides.

(Do I need to explain?)

Zig Zag Wanderer
April 2, 2019 9:56 pm

The Great Barrier Reef is fine, folks.

Come and enjoy it. Bring tourist dollars! 🙂

Paul r
April 2, 2019 10:11 pm

So let me get this straight coral reefs that have been around 200 million years or so can adapt to changing conditions……. who would’ve thought

Andrew F
Reply to  Paul r
April 2, 2019 11:32 pm

plenty apparently!

Chris Hanley
April 2, 2019 10:18 pm

“… [the] non-sequitur closing sentence is most certainly the fingerprint of another such enforced distortion that is now being superimposed on otherwise objective science …”.
That closing sentence in full is even more insupportable:
“Coral bleaching has had unprecedented negative effects on coral populations worldwide, and immediate action globally to reduce carbon emissions is necessary to avoid further declines of coral reefs …”.
Systematic coral reef monitoring is comparatively recent, for instance only since the 1970s in the Caribbean, and reliable sea surface temperature and satellite records date from around the same time that was thought at the time to be unusually cold.

Old Woman of the North
April 2, 2019 10:20 pm

Cairns is suffering lack of tourists because of the nonsensical reports about no coral – all bleached – that have been pushed by these eco-warriors who are loose with the truth.

Anthony T Ratliffe
Reply to  Old Woman of the North
April 3, 2019 3:12 am

Astute comment! There was an article in the Calgary Herald newspaper yesterday, in the Travel section. Now this is a significant regional publication in Canada. and it said some pretty silly things about the GBR.

For what it is worth, this is how I commented, not that the author will care!.

You wrote that “Australia’s Great Barrier Reef has lost roughly half of its coral since 2016 due to bleaching.”

That’s an evidence free statement – i.e. it’s simply untrue.

The status of the reef, a highly dynamic artifact, is much more nuanced than any blanket extreme claim such as yours.

Why don’t you do elementary fact checking before making wildly controversial statements? Just misleading journalism, unworthy of the Herald.


April 2, 2019 10:38 pm

This may be relevant to the topic of coral research reportage –
yesterday in The Guardian Australia, there was an alarmist story about coral bleaching occurring during March at Lord Howe Island, the most southerly coral reef on earth (~900 kms east of Sydney).

The research team from 3 universities apparently hopped on a plane to LHI and studied the bleaching for 2 weeks, came back to Oz, then announced they need to go back to LHI again this month (April) to see how the coral is doing.

My suspicion about his jaunt is that having been to LHI 4 times over the past dozen years, I know that because LHI can only take ~400 visitors at any time, you need to book flights & accommodation at least 6 months beforehand. It is a very, very, very popular tourism destination, and only one airline flies there with 34-seat planes (Dash-8s).

So I’m wondering whether the dash out to LHI to study the coral bleaching was perhaps all booked months before the event was supposed to have occurred in March. Maybe a Freedom of Information question about when the travel & accom bookings were made would yield some interesting answers

HD Hoese
Reply to  Mr.
April 3, 2019 6:38 am

I recall a relevant comment in a master’s thesis back in logic days that we don’t know what goes on between sampling periods. Marine laboratories were established to overcome that, but now are too busy writing up stuff, advertising stuff and other stuff. Back at the end of logic days some Midwestern university claimed they were best to study marine science since they were located half way between the Atlantic and Pacific. Like the Polar labs on the equator.

Besides, everybody knows you can’t put all your symbionts in one polyp.

ferd berple
Reply to  Mr.
April 3, 2019 9:41 am

Lord Howe Island is 31.5 degrees south. It is well outside the tropics. LH marks the southern boundary for coral because coral reefs do not like cold water. Any further south and you will likely find only soft corals, which are not reef building. The soft corals can tolerate colder waters than the reef building hard corals.

Patrick MJD
Reply to  Mr.
April 3, 2019 11:48 pm
April 2, 2019 11:08 pm

Half the world’s oceans are too cold for coral now, nowhere is too hot.
Warming oceans will mean more coral reefs, not less.

April 3, 2019 2:09 am

Thanks to Jim Steele for yet another informative, scientific article.

This is what we want !

April 3, 2019 2:12 am

Bad news , if you are interested in keeping the money flowing into the area of ‘coral doom’ to keep your career on track.
Expect attacks on this in 10, 9, 8,7…

April 3, 2019 2:42 am

Great article, and thank you for the reference to Sully et al. Jim.

Amazing critters those corals. Apparently one of their biggest threats is sun lotions, or so I read.

April 3, 2019 4:04 am

Big Green won’t like that research paper one bit. Dr Peter Ridd showed that you simply cannot trust Big Green research on corals that claim catastrophic consequences. Much of the research into corals is poorly done and not reproducible. Environmental activists corrupting science to push political agendas.

April 3, 2019 4:51 am

Rapid coral adaption is Gaia’s last-gasp attempt to save herself from man’s murderous assault. She is holding her volcanic arsenal in reserve. Don’t make her use it.

April 3, 2019 5:16 am

the average sea surface temperature that initiated bleaching was 82.6 °F.
This is total garbage…….I won’t even get in the water until it’s at least 88 F…
…and our corals are definitely not bleaching

it’s not the temperature…it’s how rapidly…or slowly…it gets there…it’s the zoox

Reply to  Latitude
April 3, 2019 8:53 am

That 82.6 temperature caught my eye, too. I have a photo from 1979 taken in Palau in the islands of Micronesia. It’s of an aquarium thermometer I placed between beautiful corals and giant clams. It read 91°. That temperature will fluctuate with a new incoming tide, but it was that warm for a number of hours. The ambient temperature of the top 30′ of water was closer to 86 on average.

April 3, 2019 5:56 am

The very term “coral bleaching” is a misleading prejudicial term and should be discarded as non-scientific. It implies a chemical process and man-made pollutants in the minds of the average non-specialist.

However it is named, corals have adapted marvelously to millions of years of repeated glaciation-interglacial cycles to be at their current worldwide distribution.

April 3, 2019 7:15 am

Does anyone ever mention coral bleaching caused by cold temperatures? This happened off the Florida coast a few ago

Reply to  Marcos
April 3, 2019 8:32 am

…cold is limiting…it kills
heat is not

ferd berple
Reply to  Marcos
April 3, 2019 9:57 am

The bleaching on Lord Howe could well be due to cold as LH is at the
southern boundary for hard, reef building corals.

Almost every place on earth in the tropics is surrounded by coral reefs. There are exceptions due to river runoff because fresh water and silt both kill corals. But in general corals, mangroves and mosquitoes are what greet any sailor that tries to come ashore in the tropics.

Reply to  ferd berple
April 3, 2019 1:34 pm

Being from Queensland, Australia, I shake my head every time I see a news or opinion piece about deterioration of coral reefs in the general Great Barrier Reef vicinity.

Most “evidence” presents examples that are of inshore shallow tidal zone fringing coral growths, whereas the Great Barrier Reef itself is some 100 – 250 kilometres east of the Qld coastline at any point.

I was lucky enough to fly over the entire length of the GBR at only 20,000 feet altitude in clear skies many years ago on a flight from Brisbane to Port Moresby – 2,000 kilometres.
Man that interconnected reef system is HUGE. No wonder it is visible from space!

And to assert that sampling studies show that”half the GBR is moribund from bleaching” is akin to asserting that along the whole length of the Rocky Mountains, sampling shows that half of all the conifers of all sizes are in the grip of die-back.

It doesn't add up...
April 3, 2019 1:29 pm

Meanwhile JCU doubles down by getting the Daily Mail to publish this:

It seems that readers are unimpressed to judge by the comments posted so far, although no-one has mentioned this article or Peter Ridd’s case.

Wiliam Haas
April 3, 2019 2:55 pm

Coral survived periods that were warmer than the Modern Warm Period during the Holocene. Coral survived the previous interglacial period, the Eemian, which was warmer than this one with more ice cap melting and higher sea levels.

John Reistroffer
April 3, 2019 6:16 pm

Not mentioned in the paper is the nature of coral reproduction. Many corals release egg and sperm into the water. The fertilized egg become a planula which is a planktonic organism with cilia that float in the water column until landing on a solid substrate on the water bottom. Since the planula are floaters they have a wide distribution, not just in the vicinity of the colony.
This early stage of the life cycle allows the corals to distribute themselves over a wide variety of environments. Those that land in a good place to live will eventually develop into a colony. Likewise those that don’t die.
The water column changes temperature with depth. If the water is too hot in the shallow water for the coral to live, then they will not survive, but elements of their offspring reach find a substrate which is cooler or better suited for them and they will survive and start another colony.
Therefore corals are constantly sending out colonists over a wide area around the “reef” and those that land in optimal conditions survive. So if the water is warming, cooling, rising or falling or becomes more turbid, planktonic colonists from the main colony are always floating around looking for a better place to live.
That is why you see coral benches above sea level on islands and coastlines, with active coral colonies in the water. The colonists found a decent place to live and propagate, while the main colony underwent stress which eventually leading to it’s death.

April 6, 2019 2:18 pm

Jim: Thanks for the very informative post.

IIRC, coral lived through periods before the ice ages began that were much warmer than today and presumably more acidic (less basic, if you prefer) due to higher CO2. Do we know if coral lived back then in the warmest oceans on the planet? Or did coral migrate to higher latitudes with temperatures similar to those preferred today? Coral could be bleaching and adapting today, but there may be a limit to what is currently possible and the rate at which evolution may make higher temperature possible.

In higher organisms, the location precipitation of calcium (phosphate) is controlled by active transport and probably by a protein scaffold that catalyzes precipitation. Does coral do the same thing? In the ocean, we think calcium carbonate can only exist in the presence of thermodynamic saturation – and this does determine where calcium carbonate shells are found at the bottom of the ocean. However, thermodynamic stability doesn’t control where bone is found, and it would take a long time to reach equilibrium even if it did. A coral reef is sitting on a giant reservoir of calcium ions that can provide a locally saturated amount of calcium ions for a very long time in the future. The thermodynamic stability of solid calcium carbonate in the bulk ocean may not be very relevant to the local environment of a coral reef that can be shaped by active transport of calcium ions to where they are needed and where calcium carbonate can be harvested when fluctuations in calcium ions make precipitation favorable.

%d bloggers like this:
Verified by MonsterInsights