Tag Archives: Coral Bleaching

Spotting the killer hot spots

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Killer hotspots of over-heated ocean water which destroy huge areas of coral and bring starvation to birds, fish and other sea creatures can now be pinpointed, thanks to a major advance in the use of satellite technology by Australian and American researchers.

Advanced satellites and smart mathematics are enabling the scientists to detect the events which cause mass bleaching of corals and disruption of marine food chains with unprecedented precision.

This is revealing the Great Barrier Reef’s most threatened areas under global warming.

“Until now we have only been able to detect large-scale events under typical seasonal conditions,” team leader and University of Queensland researcher Dr Scarla Weeks said.

“The new technology gives us the power to see what is happening in the ocean around the Great Barrier Reef in much finer scale in both space and time,” said Dr Scarla Weeks, of UQ’s Centre for Marine Studies (CMS) and Centre for Remote Sensing and Spatial Information Science (CRSSIS).

“It means we can identify those areas most at risk of being hit by hot water, enabling managers and reef visitors to take greater steps to protect them.

“It also means that we can observe coral bleaching events taking place, which were missedbefore because the satellite data didn’t have the fine scales necessary.”

Dr Weeks said that the 2002 bleaching event, which hit 54 per cent of the Great Barrier Reef was clearly detected using satellite data from the US National Oceans and Atmosphere Administration (NOAA) – but the subsequent 2005/6 event, which hit the southern GBR hard, was not picked up.

“One reason was the 2005/6 bleaching was an anomaly. It struck in November/December, whereas the usual time that warm water enters the GBR is in late summer, around February.

“The existing technology used didn’t have the resolution to pick it up. In fact it couldn’t observe any reefs close inshore.”

Dr Weeks’ team has announced the development of a satellite and mathematical tool that provides a dramatic improvement in the ability to read sea surface temperature anomalies from outer space. It is more accurate in time and can see much smaller areas of water.

“Using this we can identify individual reefs or groups of reefs which are most at risk of hot water and coral bleaching under climate change,” she said.

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More on the coral-sunscreen ‘issue’

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I’m not entirely sure why the “sunscreen causes coral bleaching” story is doing the rounds in the news again (see here and here – it seems to make for a very media-friendly story), but i’m still amazed at the mileage these authors are getting from a highly questionable study. I’ve debated this before on Climate Shifts with Robert Danavaro, the lead author of the study. Statements such as “New research highlights sunscreen as major cause of coral bleaching” are stretching the findings and conclusions of this paper to ridiculous extremes – the concept that “sunscreens may now be posing a significant risk to marine life” are missing the point. Durwood Dugger, the founder of the aquaculture company Biocepts wrote an excellent critique in response to my last post:

The authors conclusions “We conclude that sunscreens, by promoting viral infection, can potentially play an important role in coral bleaching in areas prone to high levels of recreational use by humans.” are neither valid or supported scientifically, they are rather the author’s theories. While pieces of this research are informative – they are informative only under the exact conditions under which they were demonstrated – improbable levels of sunscreen contaminants. Essentially they don’t support any conclusion other than in the experimental environment described in the research – that the experimental levels of various sunscreen ingredients produce increased short term viral activity.

I don’t doubt for a second that sunscreens kill corals – almost anything will cause mortality in high enough doses. A colleague of mine put this succinctly in a previous article:

“Any contaminant can experimentally damage a coral under artificially high concentrations. The amount [in the wild] must be tiny due to dilution,” commented Terry Hughes, director of the Australian Research Council’s Centre of Excellence for Coral Reef Studies at James Cook University in Queensland.

“Imagine how much water a tourist wearing one teaspoon of sunscreen swims through in an hour-long snorkel. Compared to real threats like global warming, runoff and overfishing, any impact of sunscreen is unproven and undoubtedly trivial,” he said.

“Eritrean coral reefs provide hope for global marine future” – The Age

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The Age, 16th April 2008

Silver bubbles pop to the surface as a snorkeler glides over a colourful coral reef, bright fish speeding to safety in its protective fronds. Experts say this small Horn of Africa nation has some of the most pristine coral reefs left anywhere worldwide, a “global hotspot” for marine diversity supporting thousands of species.

Known also as Green Island for its thick cover of mangroves, Sheikh Seid is only one of 354 largely uninhabited islands scattered along Eritrea’s southern Red Sea desert coast, many part of Eritrea’s Dahlak archipelago. The remote reefs are exciting scientists, who see in Eritrea’s waters a chance of hope amidst increasingly bleak predictions for the future of coral reefs — if sea temperatures rise as forecast due to global climate change.

Unlike the deeper, cooler waters elsewhere in the Red Sea, Eritrea’s large expanses of shallow — and therefore hotter — waters have created corals uniquely capable of coping with extremes of heat, scientists say.

“Eritrea has the most temperature tolerant corals in the world,”

Said marine expert Dr John ‘Charlie’ Veron, dubbed the “king of coral” for his discovery of more than a fifth of all coral species.

“That bodes well, for climate change is set to decimate coral reefs.”

Leading scientists warn that most reefs — vital for the massive levels of marine life that depend upon them and a crucial component of coastal economies — will be largely extinct by the end of the century unless greenhouse gas emissions are curbed.

They say many will be killed by mass “bleaching” and irreversible acidification of seawater caused by the absorption of carbon dioxide into surface waters, with at least 20 per cent of coral reefs worldwide already feared lost.

But with Eritrea’s surface water in summer an average bathwater temperature of 32.5 C (90.5 F) — reportedly peaking at a sweltering 37C (98.6 F) — corals here have evolved to survive in an environment that would kill others elsewhere in the world. (Read More)

Coral adaptation in the face of climate change – response by Hoegh-Guldberg et al

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We certainly hope that Baird and Maynard are right and that in the coming years corals will exhibit an adaptive capability that they have not yet exhibited in situ or in the laboratory. At this point, however, it appears unlikely.
As Baird and Maynard point out, the coral genera Acropora and Pocillopora have generation times that are short (several years) relative to the generation times of other corals. The majority of coral generation times, however, are still long (decades) relative to the accelerating pace of climate change, throwing doubt on the scope of most coral species for rapid adaptation (1).

Corals, like other organisms, can also modify the risk of coral bleaching over the short term through physiological acclimation (2). Acclimation, however, as with any phenotypic change, is limited. In the same vein, corals that form symbioses with more than one variety of dinoflagellate can shift their populations so that they are dominated by their more thermally tolerant dinoflagellate genotypes during thermal stress. Unfortunately, these short-lived changes have not yet resulted in the novel host-symbiont combinations that will be required for survival in the challenging temperatures and acidities of future oceans under rising atmospheric carbon dioxide.

It is important not to confuse genetic adaptation with the increased average thermal tolerance observed for some coral communities over the past 25 years, which has occurred largely because thermally sensitive species have died out, leaving robust species behind (3). Equally important is the lack of evidence that corals have the capacity to either acclimate or adapt to falling aragonite saturation states. It seems unlikely that genetic adaptation will solve the problems of global change facing corals. Indeed, paleontological evidence indicates that calcifying marine organisms including corals suffered a protracted period of absence after large and rapid changes in atmospheric carbon dioxide associated with the Permian-riassic extinction event (4, 5). It took millions of years for these organisms and ecosystems to recover.

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Coral adaptation in the face of climate change – Baird & Maynard

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cover.gifIn their Review, “Coral reefs under rapid climate change and ocean acidification” (14 December 2007, p. 1737), O. Hoegh-Guldberg et al. present future reef scenarios that range from coral-dominated communities to rapidly eroding rubble banks. Notably, none of their scenarios considers the capacity for corals to adapt. The authors dismiss adaptation because “[r]eef-building corals have relatively long generation times and low genetic diversity, making for slow rates of adaptation [relative to rates of change].” We think the possibility of adaptation deserves a second look.
Many features of coral life histories, such as extended life spans, delayed maturation, and colony fission, do result in long generation times (1) [some between 33 and 37 years (2)]. However, other corals, such as many species of Acropora and Pocillopora, mature early, grow rapidly, and suffer whole-colony mortality, as opposed to colony fission, after mechanical disturbances (3) and thermal stress (4). The life histories of these ecologically important and abundant species suggest an underappreciated capacity to adapt rapidly to changing environments.

Repeated bleaching episodes in the same coral assemblages and the increasing scale and frequency of coral bleaching have been cited as evidence that corals have exhausted their genetic capacity to adapt to rising sea surface temperatures (5). However, comparisons of the rates of mortality within populations among bleaching events are not available. Without these data, it is not possible to assess whether the adaptive response has been exhausted. Indeed, the effects of temperature and acidification on even the most basic vital rates in corals, such as growth, mortality, and fecundity, are largely unknown, as are the physiological trade-offs among these traits. Consequently, the sensitivity of population growth to climate-induced changes in vital rates remains almost completely unexplored [but see (6)]. In the absence of long-term demographic studies to detect temporal trends in life history traits, predicting rates of adaptation, and whether they will be exceeded by rates of environmental change, is pure speculation. Indeed, where such data are available for terrestrial organisms they demonstrate that contemporary evolution in response to climate change is possible (7).

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Coral reefs and climate change: Microbes could be the key to coral death

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Coral reefs could be dying out because of changes to the microbes that live in them just as much as from the direct rise in temperature caused by global warming, according to scientists speaking today (Wednesday 2 April 2008) at the Society for General Microbiology’s 162nd meeting being held this week at the Edinburgh International Conference Centre.Tropical ecosystems are currently balanced on a climate change knife edge. Corals in coral reefs, which are made up of animals called polyps that secrete hard external skeletons of calcium carbonate, are living perilously close to their upper temperature limits. This makes them very vulnerable to even small temperature rises of 1-2oC above the normal summer maximum.

“Many of the deaths we see in the coral reefs, which occur following coral bleaching events, when huge areas of reef die off like in 1998 when 17% of the world’s reefs were killed, can be put down to changes in the microbes which live in and around the reefs,” says Dr John Bythell, a biologist from Newcastle University. “These microbes can be thought of as being similar to the bacteria that normally live in our guts and help us digest our food.”

Changes in sea temperature caused by climate change and global warming affect corals, but they also affect the types of bacteria and other microflora that live with them. When the water warms up, some disease-causing bacteria are more successful and can attack the corals. The corals themselves suffer from heat, which reduces their defences. Also, some of the friendly bacteria that normally live in the corals’ guts become weakened, allowing other harmful bacteria to multiply and cause diseases or other problems.

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Study: Coral reefs like ‘junk food’

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United Press International, 28th March 2008

Townsville, Australia — Australian scientists have discovered coral reefs have an addiction to “junk food” and order symbiotic algae to produce it. James Cook University researchers said the symbiosis between coral, a primitive animal, and zooxanthellae — tiny one-celled plants — has not only built the largest living organism on the planet, the Great Barrier Reef, but also underpins the economies of many tropical nations.

The issue of whether the partnership is robust enough to withstand climate change is driving a worldwide scientific effort to decipher how corals and their symbiotic algae communicate, said JCU Professor David Yellowlees.

“It’s an incredibly intricate relationship in which the corals feed the algae and try to control their diet, and the algae in turn use sunlight to produce ‘junk food’ — carbohydrates and fats — for the corals to consume,” said Yellowlees. “Where it all breaks down is when heated water lingers over the reef and the corals expel the algae and then begin to slowly starve to death.

“This is the bleaching phenomenon Australians are by now so familiar with, and which is such a feature of global warming.”

Coral reef fish act as “lawnmowers” in the fight against climate change

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BBC News, 20th March

A healthy fish population could be the key to ensuring coral reefs survive the impacts of climate change, pollution, overfishing and other threats. Australian scientists found that some fish act as “lawnmowers”, keeping coral free of kelp and unwanted algae. At a briefing to parliamentarians in Canberra, they said protected areas were rebuilding fish populations in some parts of the Great Barrier Reef.

Warming seas are likely to affect the reef severely within a few decades. Pollution is also a growing problem, particularly fertilisers that wash from agricultural land into water around the reef, stimulating the growth of plants that stifle the coral. The assembled experts told parliamentarians that fish able to graze on invading plants played a vital role in the health of reef ecosystems.
“The Great Barrier Reef is still a resilient system… and herbivorous fish play a critical role in that regenerative capacity, by keeping the dead coral space free of algae, so that new juvenile coral can re-establish themselves,” said Professor Terry Hughes from James Cook University in Townsville. His research group has conducted experiments which involved building cages to keep fish away from sections of reef. They found that three times as much new coral developed in areas where the fish were present as in the caged portions.

Parrotfish in particular use their serrated jaws to scrape off incipient algae and plants. More recently, his team has also identified the rabbit fish – a brown, bland-looking species – as a potentially important harvester of seaweed. “So managing fisheries can help to maintain the reef’s resilience to future climate change,” he said. In recent years, Marine Protected Areas have been set up along the Great Barrier Reef in order to provide sanctuaries where fish and other marine creatures can grow and develop.

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Has the Great Barrier Reef got a future?

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Once I would have thought that a ridiculous question. Yet today, if we assemble all the best science we have, the answer can at best be “maybe”.

It may seem preposterous that the greatest coral reef in the world – the biggest structure made by life on Earth – could be seriously (I mean genuinely seriously) threatened by climate change. The question itself is probably already relegated in your mind to a ‘here-we-go-again’ catch-bag of greenie diatribe about the state of our planet. This view is understandable given that even a decade ago, there were many scientists who had not yet come to grips with the full implications of climate change.

Very likely you have a feeling that dire predictions about anything almost always turn out to be exaggerations. What you really think is: OK, where there’s smoke there’s fire, so there’s probably something in this to be worried about, somewhere. But, it won’t be as bad as those doom-sayers are predicting. When I started writing “A Reef in Time”, I knew that climate change was likely to have serious consequences for coral reefs, but even I was shocked to the core by what all the best science that existed was saying. In a long phase of personal anguish I turned to specialists in many different fields of science to find anything that might suggest a fault in my own conclusions. No luck. The bottom line remains: the GBR can indeed be utterly trashed in the lifetime of today’s children. That certainty is what motivates me to broadcast this message as clearly, as accurately and, yes, as loudly, as I can.

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