Tag Archives: Coral Bleaching

Death of corals is oceanographer’s murder mystery

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There is a nice story in today’s News and Observer, the local paper for the Research Triangle,  in North Carolina.  Wade Rawlins is an environmental writer who covers a range of issues.  He did an excellent job describing coral reefs, their value and threats to them, for a lay audience.  I wish we could get more basic stories like this across to the public.

“Marine scientist John Bruno became interested in coral reefs as a boy snorkeling in the turquoise waters off the Florida Keys above reefs of golden corals the size of football fields.

“It just went on for acres and acres,” recalls Bruno, 43, an associate professor at UNC-Chapel Hill. “They were just full of fish. We’d see hammerhead sharks on the reef and big critters. That is all gone. The corals are gone and the big fish are gone,” he says. “That’s happened in my lifetime.”

“It’s a wonderful murder mystery for ecologists,” says Bruno, who has been the studying the effects of disease and warming sea water on coral reefs. “It’s not obvious what the cause is. There are lots of potential culprits.”

Among the suspects are pollution, destructive fishing practices, predators that feed on corals, disease and warmer ocean waters.

In the ocean, reef-building corals, which are marine polyps, a class of animals, typically exist in colonies of many identical individuals. They fill the role of trees in a forest, Bruno says. The skeletons of corals create the hardened framework of a reef and, over time, build up and provide habitat for thousands of other animals and plants. Corals require warm, clear water and are sensitive to temperatures.

A warming of the ocean by just a degree or two for a few weeks in summer can disrupt the life cycle of corals, Bruno says. Reef-building corals contain tiny plant-like algae that live within their tissue in a mutually beneficial relationship. The algae provide the coral with food and oxygen, as well as the vibrant colors for which corals are known. In return, the organisms receive shelter and nutrients.

Read the full story here

Update on sea surface temperatures and the Great Barrier Reef

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The sea surface temperature (SST) model forecast (NOAA) for the Great Barrier Reef (GBR) is predicting widespread bleaching, with severe scenarios predicted to affect the northern GBR from mid January 2009. Predictions for the month of December suggests that the potential for bleaching from central GBR intensifying to the north will extend into 2009.  When sea surface temperature forecasts exceed bleaching thresholds and continue long enough to cause bleaching, the outlook products display the bleaching potential during the upcoming warm season.

bleachingoutlook4month_g_on_20081130_end_20090329

The NOAA Coral Reef Watch Bleaching Thermal Stress Outlook indicates that the greatest chance of bleaching during the upcoming austral summer will be in the region bounded by Papua New Guinea, the Solomon Islands, and the northern Great Barrier Reef (GBR). The figure above shows the most recent global 17-week Coral Bleaching Thermal Stress Outlook from the 09 December 2008 model run.

Actual conditions for December show temperatures around the central GBR 0.75-1.0 degrees Celsius above the MMM +1 (mean monthly maxima), and above 1 degrees Celcius to the Northern GBR and waters SE of PNG (Link). Recent SST changes have also been mapped by the Australian Bureau for Meteorology and confirm gradual warming on the GBR despite sub surface cooling in the central to eastern pacific.

vs_multiyear_heron

Current SST tracking on Heron island on the southern GBR shows temperatures following a similar profile to that of the 2001/2002 bleaching event. The increase in SST over the next month will be critical in determining the risk of bleaching across southern GBR.

The majority of dynamic computer models are predicting neutral climate conditions to continue through the southern summer, however, some models are predicting a return to La Niña conditions which may drive monsoon, storm like conditions and generate some cooling in Queensland (Link). More updates as they come.

Climate change pushes coral decline – Western Australian

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The Western Australian, 1st December 2008

The world’s marine reserves may be helping to restore local fish populations, but they are failing to protect fragile coral reefs from the harsh effects of global warming, a conference has heard.

Data collected from 8540 coral reefs in the Indian, Caribbean and Pacific regions from 1987 to 2005 show the rate of coral decline with warmer temperatures is just the same in marine reserves as in highly fished areas.

Associate Professor John Bruno from the University of North Carolina in the United States, who conducted the research, has told the Ecological Society’s annual conference the results should sound a warning bell for reef managers who believe marine reserves are more resistant to climate change.

“The biggest stresses put on coral reefs are ocean warming and disease outbreaks,” Mr Bruno told the conference at the University of Sydney on Monday.

“These stresses are regional and global in scale and local protection in marine reserves is unlikely to help these reefs resist such changes.

“Marine reserves are very important for protecting fish populations, maintaining coral reef food webs and protecting against anchor damage, but they are unlikely to reduce coral losses due to global warming,” he added.

The key to restoring and protecting coral from climate change lay in long-term regional and global strategies to combat its root causes, such as carbon dioxide emissions, Mr Bruno said.

Great Barrier Reef Marine Park Authority predicting widespread coral bleaching during the summer

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Using an experimental algorithm developed from satellite monitoring of sea surface temperatures, the National Oceanographic and Atmospheric Administration (NOAA) are able to predict (often with some accuracy) the coral bleaching outlook for the upcoming season (for more information on the model itself, see this link).The forecast for the Austral summer (Nov ’08 – Feb ’09) is intensifying, with potential ‘severe bleaching’ predicted in the Northern sectors of the GBR – so much so that the Great Barrier Reef Marine Park Authority is concerned about the rising sea temperatures.

The area most likely to suffer thermal stress with the potential for severe bleaching during the next 15 weeks is a region spanning Papua New Guinea, the Solomon Islands, and the Far Northern section of the GBR. Less severe thermal stress is a expected in a broader region including all of the Cairns section of the GBR. To the west, the model currently predicts a threat of moderate levels of thermal stress from southern Borneo across through Timor-Leste to southern Papua New Guinea and Torres Strait. This level of potential stress then picks up in the central GBR and east extending across Vanuatu and New Caledonia to the east-southeast of Fiji. Some mild stress may be seen around Madagascar. The greatest warming is expected to begin from late January through February.

It seems that the northern GBR is likely to be affected with the occurence of localised bleaching, but the impact across broader scales (i.e southern GBR) looks less severe. Given that the Bureau of Meterology are predicting a cyclone season “on the upper side of normal“, the impacts of cyclones passing through the coral sea could potentially dissapate the thermal stress build up that triggers coral bleaching (read more). We will keep posting updates on the 2008/2009 season as the bleaching outlook changes.

Coral Reef news round-up

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“Reef guide to benefit research” (Sydney Morning Herald, 26/11/08)

‘I mean we’re not going to have reefs for much longer but we can at least have them a bit longer.” Pat Hutchings, a 40-year veteran of coral reef research, is not optimistic for the long-term future of the Great Barrier Reef but she is determined to do everything within her power to help its survival.

Hutchings has been poking around reefs since her student days, before scuba diving existed outside the armed forces. “When I went to learn in the mid to late ’60s, we had to make our own wetsuits – you couldn’t buy them,” she says. “There were a few naval divers but it wasn’t available to students. Prior to that people swam around with a box with glass on the bottom to look through.” (Read More)

“Ending the reef madness”
(The Australian, 26/11/08)

OVE Hoegh-Guldberg is blunt about the gloomy prospects for the Great Barrier Reef.

“We have no time to lose,” said the director of the University of Queensland’s Centre for Marine Studies.

“We are three decades away from having a reef with no coral and less than half the species we have today. It is crunch time.”

Speaking on the eve of the publication of a unique book, The Great Barrier Reef, the first comprehensive field guide to the world’s largest continous reef, he stressed the imperative to act. “Part of the mission for us as scientists is to pass on the urgency and excitement about these issues.” (Read More)

“Climate change, starfish hit Fiji Reefs: Study”
(ABC News, 24/11/08)

Climate change and a starfish outbreak have shrunk coral reefs near Fiji, forcing locals to change their lifestyle.

A new study, published in Global Change Biology, has found that from 2000-2006 the size of coral reefs around Fiji’s remote Lau Islands contracted by about 50 per cent.

Dr Nick Graham from James Cook University, who took part in the study, says fishing and habitat disturbance are having a big impact.

“The area was disturbed by a crown of thorns starfish outbreak in about 2000 and then, the subsequent year, there was also a coral bleaching event associated with climate change,” Mr Graham said.

“We were pretty shocked at just how severe the impact was.” (Read More)

“Oceans acidifying faster than predicted, threatening shellfish”
(Bloomberg, 25/11/08)

Oceans are acidifying 10 times faster than predicted, threatening heightened damage to coral reefs and shellfish, University of Chicago scientists said.

Researchers took more than 24,000 pH measurements over eight years and found the rate at which the ocean is becoming more acidic correlates with the atmospheric concentration of carbon dioxide, or CO2, the university said in a statement. When CO2, which helps cause global warming, dissolves in water, it forms carbonic acid.

“The acidity increased more than 10 times faster than had been predicted by climate change models and other studies,” University of Chicago ecology and evolution professor Timothy Wooton said in the statement. “This increase will have a severe impact on marine food webs and suggests that ocean acidification may be a more urgent issue than previously thought.” (Read More)

MPAs and climate change II: study finds no-take reserves do not increase reef resilience

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PI Nick Graham surveying a high coral cover reef.

PI Nick Graham surveying a high coral cover reef.

Some coral reefs scientists have argued (and prayed) that marine reserves (no-take MPAs) could limit the impacts of climate change on populations of reef-building corals.  The idea is that by maintaining healthy food webs and herbivore populations, reef managers can prevent seaweed blooms that can kill juvenile corals.  Restricting fishing would thus increase reef resilience (which ecologists define as the return rate of an ecological system to its baseline state following a disturbance).  Unfortunately, a new study tempers such wishful thinking.

The study (Graham et al. 2008 published on August 27 in the open access journal PloS One) indicates that marine reserves have no effect on coral resilience to ocean warming.

Approximately 45% of coral cover in the Indian Ocean was lost in 1998 due to temperature-related coral bleaching.  To compare coral loss within and outside of reserves, the team resurveyed 66 reefs in the Indian Ocean that had originally been surveyed before the 1998 mass bleaching event.  The surveyed sites included reefs within nine reserves in four countries.

The results indicated that “A greater proportion of [marine reserves] (71%) than fished (42%) locations showed significant declines in coral cover over the study period. There was no evidence to suggest the percent change in coral cover differed between [marine reserves] and fished areas, and in some cases declines were significantly greater in [marine reserves]”

This is an important study in coral reef ecology.  As a believer in Macroecology and a long-time disciple of James Brown (the desert ecologist, not the King of Funk) I think such a regional-scale, carefully implemented approach could be used to answer many other key questions in reef ecology.  Having read hundreds of monitoring studies while building a database of >10,000 reef surveys, I can attest that there are few targeted macroecological reef studies of this scope.  There are some monitoring programs this large.  But few studies of this scale are designed and implemented to answer a specific question.  Although the macroecological approach is rarely employed (due to obvious financial and logistical constraints), it certainly isn’t new.  Terry Hughes (Hughes 1994 Science) applied it by resurveying nine reefs on the north coast of Jamaica after a variety of disturbances wiped out corals and enabled macroalgae to become the dominant benthic organism.  Even earlier, Endean and Stablum surveyed dozens of reefs across the GBR in the late 1960s and early 1970s to assess the impact of and recovery from a regional crown-of-thorns starfish outbreak.

I imagine critics of Graham et al. 2008 and it’s implications could argue that many or most tropical marine reserves are not well-managed and that they might increase resilience if enforced.  This would be a fair point, but given the political and socio-economic realities of the region, poaching might be difficult or impossible to eliminate.  So to paraphrase Donald Rumsfeld, we might just have to conserve reefs with the marine reserves we have, not the marine reserves we want.

Change in coral cover at sites across the western Indian Ocean

Change in coral cover at sites across the western Indian Ocean. Green and red symbols represent increases and decreases in coral cover respectively. Symbols with solid borders are sites in marine reserves. Data represent 66 sites across the region. Numbers in key (size of bubble) are percent changes between mid 1990s and 2005.

Australian coral reefs in the news: past, present, future

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“Ancient reef found in outback” (Courier News, September 22nd, 2008)

AN ancient underwater reef discovered in Australia’s outback could unlock the secrets of the world’s climate change history, scientists said.

Located in South Australia’s Flinders Ranges, the 650-million-year-old reef existed during a period of tropical climate between two major ice age events, scientist Jonathan Giddings said in a media release today.

(Link to full story)

Explorers Find Hundreds Of Undescribed Corals (Science Daily, 19th September, 2008)

Hundreds of new kinds of animal species surprised international researchers systematically exploring waters off two islands on the Great Barrier Reef and a reef off northwestern Australia — waters long familiar to divers.

The expeditions, affiliated with the global Census of Marine Life, help mark the International Year of the Reef and included the first systematic scientific inventory of spectacular soft corals, named octocorals for the eight tentacles that fringe each polyp.

(Link to full story)

Distance no barrier to reef care (The Australian, September 23rd, 2008)

THE Australian Institute of Marine Science has begun using one of the world’s first reef-based internet protocol networks to monitor the impact of destructive forces on the Great Barrier Reef.

Using waterproof Next G modems, adaptive sensor equipment and solar-powered buoys to float the devices, AIMS has installed two wireless IP networks that can transmit data in real time up to 100km offshore.

“We’ve been hit by a number of coral-bleaching events over the past 10 years but until now we’ve had no way to monitor the causes unless we’ve been there in person,” Great Barrier Reef Observing System project manager Scott Bainbridge said.

(Link to full story)

Kingman Atoll, MPAs and climate change

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A by Zafer Kizilkaya, B by Jennifer Smith.

Top predators and coral cover on Kingman Atoll. Photo credits: A by Zafer Kizilkaya, B by Jennifer Smith

The key drivers of anthropogenic coral mortality and loss are nearly all regional- to global-scale stressors, including ocean warming and acidification, and coral predator and disease outbreaks.  Yet some scientists hope to mitigate these threats locally through fisheries regulations, such as the implementation of Marine Protected Area (MPAs) designed to increase “reef resilience”.  By limiting or preventing fishing and other extractive activities, MPAs have been relatively successful in restoring populations of overharvested fish and invertebrates.  MPAs could also, in theory, benefit corals by restoring coral reef food webs and more directly by preventing destructive fishing practices and anchor damage.  But can MPAs mitigate the effects of climate change?

In a paper recently published in the open access journal PloS One, Sandin et al. (2008), argue that the answer is “Yes”.  Co-author Nancy Knowlton stated “These remote healthy reefs clearly show that local protection can make reefs resilient to the impacts of global change”.  And lead author Stuart Sandin said “the healthier reefs showed the capacity to recover from climate change events…when the ecosystem structure is intact, the corals appear to bounce back better from previous warm water events that have killed coral.”

The study described a multifacited survey of four reefs in the northern Line Islands.  Reefs differed considerably along a gradient of proximity to people; more remote reefs had more large predators, fewer herbivores and higher coral cover.  The positive relationship between coral cover and predator biomass (in the non-statistical sense that the reef with the most fish had the most coral) led to the conclusion that “protection from overfishing and pollution appears to increase the resilience of reef ecosystems to the effects of global warming.”

If true this would be a remarkable finding.  For a variety of other reasons we clearly need to get a handle on greenhouse emissions and climate change.  But until we do, perhaps MPAs could preserve reef ecosystems, or at least minimize reef degradation.  However, nearly all of my colleagues that I have spoken to about this study and the potential of MPAs remain skeptical, mainly because MPAs cannot directly regulate or eliminate the primary culprits of anthropogenic coral loss.

In an op-ed describing the impact of the new the Papahanaumokuakea Marine National Monument in the Northwest Hawaiian Islands, Enric Sala (the Line Islands expedition leader) argued, “A national monument can protect against the decimation of sharks, groupers and jacks by fishing, but it cannot protect against global threats to marine life such as global warming and marine debris…Increased temperatures and currents do not respect national monument boundaries.”  William Precht, a coral reef geologist and restoration specialist for the Florida Keys National Marine Sanctuary, added “Data from throughout the Caribbean and western Atlantic indicate that no form of local stewardship or management could have protected coral populations from their major sources of mortality (pandemic diseases, regional coral bleaching, and severe storms) or changed the overall trajectory of coral loss observed during the past few decades.”

The Line Islands study could have been a nice natural experiment, testing the efficacy of MPAs in mitigating climate change, had nature cooperated.  Unfortunately, it didn’t, and the temperature stress gradient and the fishing intensity gradient were positively correlated, confounding the test and any interpretation of the mechanisms underlying the observed variability in coral cover.  The reef with virtually no fishing and the most predators (Kingman) also has not experienced any significant warming or warm periods over the last decade.  Was the high coral cover caused by the lack of fishing or the lack of bleaching?  And could the high coral cover be in part responsible for the plentiful fish populations on Kingman reef?  Further study and a second expedition seem warranted.  I hereby place my name on the top of the volunteer list.

In my view, the strength and novel contribution of the study is the comprehensive assessment of a pristine marine ecosystem.  As a community ecologist who is far more interested in food webs than microbes, the thing that I found fascinating about the Sandin et al. study was the inverted trophic pyramid at Kingman Atoll; the biomass of top predators was far greater than that of their prey.  Herbivorous fish were scarce and frightened, which makes me wonder why macroalgal cover was so low.  I suspect this was due to grazing by urchins, which were most abundant at Kingman, probably because their predators were being suppressed by higher level consumers.  Despite it’s limitations, the Sandin et al. study demonstrates a powerful macroecologial approach that could be used to test a key hypothesis in coral reef ecology and conservation.

Two new studies on coral symbiont specificity released in the Proceedings of the National Academy of Sciences

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"Dedicated partnership may be corals weakness"

(Sampayo et al 2008, PNAS 105[30] 10444-10449)

"Great Barrier Reef coral communities may not be able to recover from bleaching as easily as previously proposed, according to new UQ research. A two-year study by a team of UQ researchers, in the Centre for Marine Studies, has found that contrary to popular theory, it is not possible for bleached corals to recover or become more resistant to bleaching by taking up more heat tolerant species of their micro-algae partners. All corals have a symbiotic (sharing relationship) with single-celled dinoflagellates, commonly referred to as zooxanthellae. The coral provides a habitat for the zooxanthellae, which in turn produce essential nutrients for the corals.  Under stressful conditions, such as high or low water temperatures, the symbiotic zooxanthellae are expelled from their host, causing a whitening of the coral tissue or bleaching.  Coral bleaching events have caused significant mortality of corals worldwide and the frequency as well as intensity of bleaching events is predicted to increase as a result of climate change. Dr Eugenia Sampayo, who performed the research as part of her PhD, said past research had suggested that bleached corals could take up new, more tolerant symbionts, which would make them less susceptible to future bleaching events" (Read more)

 

 

"New indicator uncovered that can predict coral health"

(Stat et al 2008, PNAS 105[27] 9256-9261)

A new indicator of coral health has been discovered in a community of microscopic single-celled algae called dinoflagellates. The study, released in the July 8th edition of the journal Proceedings of the National Academy of Sciences, reveals that a particular type of these algae renders corals more susceptible to disease. "Corals are fascinating organisms whose survival is dependent on dinoflagellates that live inside the coral’s tissue," says lead author Michael Stat, an assistant researcher at the Hawaii Institute for Marine Biology (HIMB) at the University of Hawaii at Manoa. "The relationship between these dinoflagellates and corals has long been considered mutually beneficial, with the dinoflagellates supplying the coral with food via photosynthesis in return for recycled nutrients and shelter. Over the last 20 years it has been made clear that there are many different types of dinoflagellates in corals and that the unions or symbiosis between a given coral and their dinoflagellates can be very specific." It had previously been considered that all dinoflagellates found in coral are equally beneficial to their coral host, but in this study Stat, along with HIMB researchers Ruth Gates and Emily Morris, present evidence that a particular type of dinoflagellate can be found in corals that are diseased or show evidence of having had a disease. (Read more)