Scientists: Caribbean coral die-off may be worst ever, Southeast Asia and Indian Ocean bleaching “may prove to be the worst such event known to science.

Scientists studying Caribbean reefs say that 2010 may be the worst year ever for coral death there. Abnormally warm water since June appears to have dealt a blow to shallow and deep-sea corals that is likely to top the devastation of 2005, when 80% of corals were bleached and as many as 40% died in areas on the eastern side of the Caribbean.

So Eli Kintisch reports at Science online.  He explains:

Bleaching occurs when crucial microorganisms leave coral reefs during stress. Corals, which shelter a quarter or more of all marine species, get bleached, and may die, after prolonged heating. A few weeks of water temperatures a few degrees above normal can be fatal. During the 2005 die-off, for example, water temperatures off the Virgin Islands rose just 3°C above the average in August””but stayed that way until November. “There has been little recovery in the Caribbean since,” says reef specialist C. Mark Eakin of the U.S. National Oceanic and Atmospheric Administration (NOAA) in Silver Spring, Maryland.

But, as this NOAA graphic shows, 2010 is worse than 2005:

Caption:  “The extent of warming in the Caribbean is more devastating in 2010 than in 2005, previously the worst year for bleaching there.”

Kintisch reports:

“I’ve never seen bleaching like [it] in Panama,” said Nancy Knowlton, a coral biologist at the Smithsonian Tropical Research Institute in Panama who has been studying the local flora for 25 years. She and colleague Hector Guzman have seen massive reefs die in recent weeks in the enclosed lagoon of Bocas del Toro in Panama after becoming coated with giant sheets of slime, the remains of dead microorganisms. “This is NOT a normal condition on reefs, even bleached reefs. Where last year there were healthy corals, this year there was only gray ooze,” she wrote in an e-mail….

A number of factors besides water temperature can cause coral bleaching and die-offs, including pollution and storms. But temperature is the number-one culprit in such a massive die-off, says Eakin. The warmest 12-month period in the NASA temperature record ended this summer; June through August was the fourth-warmest such period in the record. The extent of the devastation across the Caribbean will become clear in the coming months as biologists measure the deaths.

The rest of this post is from Nick Sundt’s piece on the WWF blog, “Scientists Report One of the Worst Coral Bleaching Events on Record in Southeast Asia and the Indian Ocean.”

The Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies said in press release yesterday (Worst coral death strikes at SE Asia, 19 October 2010) that

“[m]any reefs are dead or dying across the Indian Ocean and into the Coral Triangle following a bleaching event that extends from the Seychelles in the west to Sulawesi and the Philippines in the east and include reefs in Sri Lanka, Burma, Thailand, Malaysia, Singapore, and many sites in western and eastern Indonesia.”

“It is certainly the worst coral die-off we have seen since 1998.  It may prove to be the worst such event known to science,” says Dr Andrew Baird of the ARC Centre.

The Coral Triangle — bordered by Indonesia, Malaysia and the Philippines — is one of WWF’s priority areas.  It covers just one percent of the Earth’s surface, but is home to fully 30 percent of the world’s coral reefs, 76 percent of reef-building coral species and more than 35 percent of coral reef fish species. It also serves as vital spawning grounds for other economically important fish such as tuna.

Coral Bleaching HotSpots, 18 Oct 2010. Source: NOAA

Above: Coral Bleaching HotSpots, 18 October 2010.  The Coral Triangle is in the lower left hand area.  According to NOAA, the map “highlights regions where the SST is currently warmer than the highest climatological monthly mean SST for that location. The HotSpot value of 1.0 °C is a threshold for thermal stress leading to coral bleaching. To highlight this threshold, HotSpot values below 1.0 °C are shown in purple, and HotSpots of 1.0 °C or greater range from yellow to red.” Source: NOAA’s Coral Hotspots Web site.

“This widespread bleaching is alarming because it directly affects the health of our oceans and their ability to nurture fish stocks and other marine resources on which millions of people depend for food and income” said Richard Leck, Climate Change Strategy Leader of the WWF Coral Triangle Programme, in a press release from WWF International on 29 July (Mass coral bleaching closes dive sites, threatens future of world’s most diverse marine region).

“So far around 80 percent of Acropora colonies and 50 per cent of colonies from other species have died since the outbreak began in May this year,”says ARC’s Dr Baird.

According to the National Oceanic and Atmospheric Administration (NOAA), global sea surface temperatures (SSTs) from January through September were at their 2nd highest on record — behind only 2005.  An El Nino was in place in the Tropical Pacific earlier this year and contributed to the warmer global average SSTs.  However, the El Nino dissipated in May and by July a La Nina — characterized by cooler surface waters —  was developing across the central and eastern equatorial Pacific Ocean.  By September the La Nina was well established, though global SSTs still were the 9th warmest on record. Of the eight warmer Septembers, all but one (in 1997) were during the last decade.

According to the ARC press release:

“[C]oral cover in the region could drop from an average of 50% to around 10%, and the spatial scale of the event could mean it will take years to recover, striking at local fishing and regional tourism industries, he says.

`Although the Coral Triangle is the richest region for corals on Earth, it relies on other regions around its fringes to supply the coral spawn and fish larvae that help keep it so rich,” Dr Baird explains. “So there are both direct and indirect effects on CT reefs which will affect their ability to recover from future disturbance.’

`Also the reefs of the region support tens of millions of people who make their living from the sea and so plays a vital role in both the regional economy and political stability. For example, in Aceh, northern Sumatra, where the bleaching is most severe, a high proportion of the people rely on fishing and tourism for their livelihoods. While it may take up to two years for some fish species to be affected by the loss of coral habitat, fisheries yields will decline and this combined with a drop in the number of SCUBA divers visiting could have major long-term effects on the local economy.’

The cause of the bleaching event was a large pool of super-hot water which swept into the eastern Indian Ocean region several months ago, shocking the corals and causing them to shed the symbiotic algae that nourish them, thereby losing color and `bleaching.’  If the corals do not regain their algae they starve to death.

According to the National Oceanic and Atmospheric Administration’s Coral Hotspots website, sea surface temperatures in the region peaked in late May, 2010, and by July the accumulated heat stress was greater than in 1998. Local dive operators recorded water temperatures of 34 C, over 4 degrees higher that than long term average for the area.

The event was first detected on reefs in Aceh by marine ecologists from Wildlife Conservation Society, CoECRS and Syiah Kuala University.  They already rate it  as one of the worst coral diebacks ever recorded.

`My colleagues and I have high confidence these successive ocean warming episodes, which exceed the normal tolerance range of warm-water corals, are driven by human-induced global warming. They underline that the planet is already taking heavy hits from climate change – and will continue to do so unless we can reduce carbon emissions very quickly.

`They also show this is not just about warmer temperatures: it is also threatening the livelihoods of tens of millions of people and potentially the stability of our region.'”

WWF Report Assesses Threats and Provides Solutions

In May 2009, WWF released a report, The Coral Triangle and Climate Change: Ecosystems, People and Societies at Risk, on the threat posed by climate change to the Coral Triangle. “This area is the planet’s crown jewel of coral diversity and we are watching it disappear before our eyes,” said Catherine Plume, Director of the Coral Triangle Program for WWF-US, when the report was released. “But as this study shows, there are opportunities to prevent this tragedy while sustaining the livelihoods of millions who rely on its riches.”

The report describes in stark terms the consequences of allowing the continued rapid increase of greenhouse gases in the atmosphere and of not addressing other threats.

“In one scenario, we continue along our current climate trajectory and do little to protect coastal environments from the onslaught of local threats,” said Queensland University Professor Ove Hoegh-Guldberg, who led the study. “In this world, people see the biological treasures of the Coral Triangle destroyed over the course of the century by rapid increases in ocean temperature, acidity and sea level, while the resilience of coastal environments also deteriorates under faltering coastal management. Poverty increases, food security plummets, economies suffer and coastal people migrate increasingly to urban areas.”

But there are alternatives to that future.  People around the planet can aggressively curb greenhouse gas emissions, and in the Coral Triangle investments can be made in strengthening the region’s natural environments, solutions that would help to build a resilient and robust Coral Triangle in which economic growth, food security and natural environments are maintained.

“Climate change in the Coral Triangle is challenging but manageable, and the region would respond well to reductions in local environmental stresses from overfishing, pollution, and declining coastal water quality and health,”  Hoegh-Guldberg said.

Even under the best case scenario however, communities  in the region can expect to experience  dramatic losses of coral, rising sea levels, increased storm activity, severe droughts and reduced food availability from coastal fisheries. But effective management of coastal resources would mean the communities would be less vulnerable and better able to adapt in the face of such hardships.

Online Resources

Worst coral death strikes at SE Asia .  Press release (19 October 2010) from The Australian Research Council (ARC) Centre of Excellence for Coral Reef Studies.

Centre of Excellence for Coral Reef Studies (Australian Research Council).  Includes a Coral Triangle Initiative.

Reef Manager’s Guide To Coral Bleaching

Climate Change and Coral Reefs: Consequences of Inaction [PDF]. By the Global Coral Reef Monitoring Network and International Coral Reef Initiative. November 2009

Coral Reefs Under Rapid Climate Change and Ocean Acidification. By O. Hoegh-Guldberg et al.Science 14 December 2007: Vol. 318. no. 5857, pp. 1737 – 1742

Scripps-Led Studies on Coral Bleaching Show Ocean Health Plays Vital Role in Coral Reef Recovery. Press release (20 August 2009) from Scripps Institution of Oceanography.


12 Responses to Scientists: Caribbean coral die-off may be worst ever, Southeast Asia and Indian Ocean bleaching “may prove to be the worst such event known to science.

  1. Richard Brenne says:

    Also warming and acidifying oceans: Our tears.

  2. fj2 says:

    Rapid reduction of emissions and removal of CO2 from the world’s oceans may be the most expedient way; those floating wind turbines detailed in today’s global warming news are most interesting as energy will be required.

  3. MapleLeaf says:

    But Roy Spencer is telling his readers that the oceans are cooling ;)

    Seriously though, this is very unfortunate and sad, and these bleaching events are just going to become more and more frequent.

  4. Michael W says:

    “A few weeks of water temperatures a few degrees above normal can be fatal.”

    Joe, with this kind of sensitivity, I don’t understand how coral reefs can exist at all. Is there data showing the Caribbean climate to have this level of stability?

    [JR: Tropics are generally very stable in temps, which is why they are so vulnerable to climate change even though most of the warming will be in the higher latitudes.]

  5. Steve L says:

    I’m waiting to hear about changes in the make-up of the coral communities, such that species that are more resistant/resilient come to dominate the reefs and keep them going (the weeds) while the other species become less common (the old growth). We’ll still have reefs, right? They’ll just have different species.
    Waiting. Waiting. … Waiting?

  6. mikkel says:

    How long does it take “dead” coral to revitalize? Whenever you hear about coral structures it’s always about the length of time to build it up (i.e. be careful boating or you may destroy something that will take three hundred years to recover) but I haven’t ever read a clear estimate of how quickly reefs can be reborn into the same structure if they don’t have to start all over again.

  7. Paulm says:

    It is possible that we are undergoing one of the most accelerated global warnings in the earths modern history due to a). Man made co2 b) relatively high level of solar energy.

    If this is so we are going to see the most rapid and catastrophic breakup of the ice sheets, surely as severe as anything we have observed in the past. This indeed means we are probably going to see meter level rises before 2100 in quite unpredictable surges.

    The global deviation of the coral reefs seems to be an important clue of the accelerated global temperature rise and is a pretty terrifying signal when all is considered.

  8. Michael W @ #4

    You’ll find a simple explanation of the conditions that cause coral bleaching at pages 6-7 of Marshall & Schuttenburg (2006) “Reef Manager’s Guide to Coral Bleaching” that Joe linked to in his online resources at the end of the post. It’s temperatures above the normal maximum temperatures combined with light that cause the damage as Marshall & Schuttenburg (2006) explain at page 6:

    “The primary cause of regional, or mass, bleaching events is increased sea temperatures. Sea temperature increases of 1-2ºC above the long term average maximum are all that are required to trigger mass bleaching. Both the intensity and duration of temperature anomalies are important in determining the timing and severity of bleaching responses. Higher temperatures can cause bleaching over a shorter exposure time, while lower temperatures require longer exposure times. While temperature is the trigger for bleaching, light also influences the severity of bleaching impacts.”

  9. Mikkel @ #6

    Corals can recover from mild bleaching but severe bleaching causes widespread mortality. If corals die the normal coral recruitment processes occur whereby coral larvae settle and begin to grow. It could take decades or centuries for a reef to recover fully but it eventually would if no more bleaching was to occur (and other pressures such as over-fishing and pollution were properly managed).

    A major concern with increased coral bleaching due to climate change is that coral bleaching events will become widespread, regular events that do not allow reefs to recover. See: Ove Hoegh-Guldberg (1999) “Climate change, coral bleaching and the future of the world’s coral reefs” Marine and Freshwater Research, Vol. 50 No. 8 Pages 839 – 866, available at

    Marshall & Schuttenberg (2006) “Reef Manager’s Guide to Coral Bleaching” that Joe linked to in his online resources at the end of the post has a very interesting series of pictures on page 12 showing the recovery process. The pictures show the same section of a reef in 1998 (when it bleached severely) then 2002 (with the dead coral covered in brown algal slime) and 2004 (when early recruitment is apparent). See

  10. mikkel says:

    Thanks Chris. Yeah the resilience document is right on and why I put “dead” in quotes. The ecosystem has layered interactions to recover acute mortality but like you said if it becomes very widespread then recovery becomes a lot more uncertain. In addition the affect of acidification, overfishing and other environmental stressors work on other parts of the ecosystem and reduce resiliency and recovery. It looks like sudden ecosystem collapse isn’t out of the question at all.

  11. Michael W says:

    “die-off may be worst ever”

    Chris, do you know how long we have been studying coral bleaching? I’m seeing a 2 decade comment in most of the studies, and Nancy Knowlton has been studying local coral in Panama for 25 years.
    It doesn’t seem like one can have an proper analysis unless we have a baseline for what is normal. How often has bleaching and coral die-off/recovery occurred?

  12. Simon D says:

    There are few records of “mass” coral bleaching before the early 1980s, probably due to both a lack of occurences and a lack of monitoring.

    We did a study three years ago which found that without the effect of human activity on the climate, the “hot spot” that caused the 2005 Caribbean bleaching event would be on the order of once in a thousand year event. Interesting to see a similar hot spot appear again five years later. See: