Heron Island Climate Change Observatory video


It is not often you get to work with someone as remarkable as Sir David Attenborough.  Earlier this year, we worked with the BBC to capture the installation of our Free Ocean Carbon Enrichment experiment on the reef crest at Heron Island.

This is a challenging experiment which is a collaboration between our lab, Stanford University and the Monterey Bay Aquarium Research Institute in which we are trying to chemically alter water flowing over a living and intact coral reef.  We want to do this for relatively long periods of time.  This is part of our push to establish unrivalled facilities on Heron island for studying the impact of climate change and ocean acidification on coral reefs.

The project it has been led by one of our postdoctoral fellows, Dr. David Kline.  Have a look at the film and I think you understand what a remarkable task of this has been!

Here is a recent press release: The Coral Reef Ecology Lab of the Global Change Institute has developed the world’s first climate change observatory on Heron Island.

Researchers from the Hoegh-Guldberg/Dove Coral Reef Ecology lab, have installed a new experimental system on the Heron Island reef flat to study the impacts of future predicted levels of CO2 on coral reef communities. The Heron Island Climate Change Observatory was funded by an ARC LIEF grant to examine the impact of rising CO2 levels in the coral reef environment for the first time.

The Coral Proto Free Ocean Carbon Enrichment (CP-FOCE) system was designed to add low pH water into experimental chambers on the reef to stimulate pH levels predicted to occur on coral reefs in the next 50-100 years. The experimental system has four chambers that will be used for well replicated, long term studies of climate change impacts on coral reefs. Additionally the system includes a network of over 20 high precision instruments that will allow the monitoring of the already changing water chemistry conditions on coral reefs. The development of this climate change observatory is being led by Prof. Hoegh-Guldberg along with Dr. David Kline, Aaron Chai and Thomas Miard of the Hoegh-Guldberg/Dove lab and Malcolm Marker from UQ engineering

Free Ocean Carbon Enrichment experimentClimate change and ocean acidification are widely recognized as key threats to Australia’s natural ecosystems, yet we are currently ill-equipped to respond due to poor knowledge of the scale/nature of the impacts. The Heron Island Climate Change Observatory will establish key infrastructure that will rapidly improve our understanding of the impacts of ocean acidification which is important to local communities and the nation given that coral reefs support over $6 billion in revenue (and employ 60,000 people) each year. This critically important information is essential to the management and protection of Australia’s coral reefs, including the Great Barrier Reef.

Featured in the BBC documentary by Sir David Attenborough “Death of the Oceans”


2010 Caribbean and SE Asia coral bleaching could be worst ever

The hottest January – September 2010 period on record has driven a massive coral bleaching event in the northern hemisphere.

Eli Kintisch reports at Science online:

“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.”

The situation is equally grim in South-East Asia. Dr Andrew Baird of the ARC Centre for Excellence for Coral Reef Studies at James Cook University reports that across the Indian Ocean and into the Coral Triangle from the Seychelles in the west to Sulawesi and the Philippines in the east and including reefs in Sri Lanka, Burma, Thailand, Malaysia, Singapore and 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. So far around 80 percent of Acropora colonies and 50 percent of colonies from other species have died since the outbreak began in May this year.”

It remains to be seen whether the extreme water temperatures experienced during the northern hemisphere summer will continue into the southern hemisphere 2010/2011 summer and affect coral reefs south of the equator such as the Great Barrier Reef.

Hat-tip: Joe Romm at Climate Progress

Related posts: Coral reefs are bleaching worldwide

Coral reefs sending a warning signal – A note from Drew Harvell

I work at an inland university in chilly upstate New York. Around here, many people feel a little global warming is good and there is really nothing that they can see or hear that will make them feel differently. News of warming sea surfaces and bleached coral reefs inspire little response when there’s a chill in the air and the ocean is hundreds of miles away.

Sure, the ice is off the lakes a few weeks earlier and the growing season is a couple of weeks longer. But there are costs we are seeing now — mosquitoes, ticks and other species of insects are really thriving with the warmer weather while some species of trees, like sugar maple, are suffering slow declines.

However, none of these small, incremental impacts gives one a sense of imminent disaster, but the reality is that increased sea-surface temperatures will impact hundreds of millions of people, whether they live in Key West or Kalamazoo.

In contrast to the incremental changes we are seeing here in the heartland, the sea is already undergoing catastrophic changes on a massive scale, ones that are unprecedented in human history and that may be largely irreversible on human time scales.

(Read more over @ CNN)

Coral reefs are bleaching worldwide


Kuwait loses 90 % of corals reefs in the Arab Gulf

“The comprehensive survey, conducted by the team, included the major locations of coral reefs 50 miles along the shores and 70 km from the southern coast borders, with depths ranging from 1-13 meters.”

Scientists watching V.I. coral bleaching

“The water temperatures have been warm for almost a year,” he said. “The corals have been stressed; they haven’t had their usual environment, as far as water temperatures go. A third to a half are experiencing some level of paling, very few corals are 100 percent bleached, which means stark white,” Smith said.”

Predicting coral bleaching in Kimbe Bay

“Most of the bleached corals were from susceptible genera like branching and plate Acropora, with a few massive and mushroom corals also bleached.  Bleaching was quite mild with 1-2% of corals bleached from 3-25m deep.  There was more bleaching in shallow water (5-10%), but this was probably related to unusually low tides at the time.”

Widespread Coral Bleaching In Sepanggar Bay Serves As Reminder

“The recent discovery of widespread coral bleaching off Sepanggar Bay should serve as a reminder that the marine ecosystem demands attention, Universiti Malaysia Sabah (UMS) Director of Borneo Marine Research Institute Prof Dr Saleem Mustafa said.”

Climate Changes Causes Massive Coral Die-Off Underway Globally

“…last month scientists with the Wildlife Conservation Society reported on what they say is one of the most rapid and severe coral mortality events ever recorded, unfolding in Indonesia.”

NOAA: Coral Bleaching Likely in Caribbean This Year

“Large areas of the southeastern Caribbean Sea are experiencing thermal stress capable of causing coral bleaching. The western Gulf of Mexico and the southern portion of the Bahamas have also experienced significant bleaching thermal stress.”

Philippine coral reefs – in hot water

“Since last May, the water temperature of the western Philippines (from Luzon to the Visayas, Palawan and Mindanao) has been 2 to 3°C above normal. The abnormally high water temperature is killing plenty of coral.”

Extreme Heat Bleaches Coral, and Threat Is Seen

Just when my friend Andrew Bolt thought it was safe to go in the water again, up jumps this ominous New York Times article.

By JUSTIN GILLIS, New York Times, Septempber 20, 2010

This year’s extreme heat is putting the world’s coral reefs under such severe stress that scientists fear widespread die-offs, endangering not only the richest ecosystems in the ocean but also fisheries that feed millions of people.

From Thailand to Texas, corals are reacting to the heat stress by bleaching, or shedding their color and going into survival mode. Many have already died, and more are expected to do so in coming months. Computer forecasts of water temperature suggest that corals in the Caribbean may undergo drastic bleaching in the next few weeks.

What is unfolding this year is only the second known global bleaching of coral reefs. Scientists are holding out hope that this year will not be as bad, over all, as 1998, the hottest year in the historical record, when an estimated 16 percent of the world’s shallow-water reefs died. But in some places, including Thailand, the situation is looking worse than in 1998.

Scientists say the trouble with the reefs is linked to climate change. For years they have warned that corals, highly sensitive to excess heat, would serve as an early indicator of the ecological distress on the planet caused by the buildup of greenhouse gases.

“I am significantly depressed by the whole situation,” said Clive Wilkinson, director of the Global Coral Reef Monitoring Network, an organization in Australia that is tracking this year’s disaster.

According to the National Oceanic and Atmospheric Administration, the first eight months of 2010 matched 1998 as the hottest January to August period on record. High ocean temperatures are taxing the organisms most sensitive to them, the shallow-water corals that create some of the world’s most vibrant and colorful seascapes.

Coral reefs occupy a tiny fraction of the ocean, but they harbor perhaps a quarter of all marine species, including a profusion of fish. Often called the rain forests of the sea, they are the foundation not only of important fishing industries but also of tourist economies worth billions.

Drastic die-offs of coral were seen for the first time in 1983 in the eastern Pacific and the Caribbean, during a large-scale weather event known as El Niño. During an El Niño, warm waters normally confined to the western Pacific flow to the east; 2010 is also an El Niño year.

Serious regional bleaching has occurred intermittently since the 1983 disaster. It is clear that natural weather variability plays a role in overheating the reefs, but scientists say it cannot, by itself, explain what has become a recurring phenomenon.

“It is a lot easier for oceans to heat up above the corals’ thresholds for bleaching when climate change is warming the baseline temperatures,” said C. Mark Eakin, who runs a program called Coral Reef Watch for the National Oceanic and Atmospheric Administration. “If you get an event like El Niño or you just get a hot summer, it’s going to be on top of the warmest temperatures we’ve ever seen.”

Coral reefs are made up of millions of tiny animals, called polyps, that form symbiotic relationships with algae. The polyps essentially act as farmers, supplying the algae with nutrients and a place to live. The algae in turn capture sunlight and carbon dioxide to make sugars that feed the coral polyps.

The captive algae give reefs their brilliant colors. Many reef fish sport fantastical colors and patterns themselves, as though dressing to match their surroundings.

Coral bleaching occurs when high heat and bright sunshine cause the metabolism of the algae to speed out of control, and they start creating toxins. The polyps essentially recoil. “The algae are spat out,” Dr. Wilkinson said.

The corals look white afterward, as though they have been bleached. If temperatures drop, the corals’ few remaining algae can reproduce and help the polyps recover. But corals are vulnerable to disease in their denuded condition, and if the heat stress continues, the corals starve to death.

Even on dead reefs, new coral polyps will often take hold, though the overall ecology of the reef may be permanently altered. The worst case is that a reef dies and never recovers.

In dozens of small island nations and on some coasts of Indonesia and the Philippines, people rely heavily on reef fish for food. When corals die, the fish are not immediately doomed, but if the coral polyps do not recover, the reef can eventually collapse, scientists say, leaving the fishery far less productive.

Research shows that is already happening in parts of the Caribbean, though people there are not as dependent on fishing as those living on Pacific islands.

It will be months before this year’s toll is known for sure. But scientists tracking the fate of corals say they have already seen widespread bleaching in Southeast Asia and the western Pacific, with corals in Thailand, parts of Indonesia and some smaller island nations being hit especially hard earlier this year.

Temperatures have since cooled in the western Pacific, and the immediate crisis has passed there, even as it accelerates in places like the Caribbean, where the waters are still warming. Serious bleaching has been seen recently in the Flower Garden Banks, a marine sanctuary off the Texas-Louisiana border.

In Thailand, “there some signs of recovery in places,” said James True, a biologist at Prince of Songkla University. But in other spots, he said, corals were hit so hard that it was not clear young polyps would be available from nearby areas to repopulate dead reefs.

“The concern we have now is that the bleaching is so widespread that potential source reefs upstream have been affected,” Dr. True said.

Even in a hot year, of course, climate varies considerably from place to place. The water temperatures in the Florida Keys are only slightly above normal this year, and the beloved reefs of that region have so far escaped serious harm.

Parts of the northern Caribbean, including the United States Virgin Islands, saw incipient bleaching this summer, but the tropical storms and hurricanes moving through the Atlantic have cooled the water there and may have saved some corals. Farther south, though, temperatures are still remarkably high, putting many Caribbean reefs at risk.

Summer is only just beginning in the Southern Hemisphere, but water temperatures off Australia are also above normal, and some scientists are worried about the single most impressive reef on earth. The best hope now, Dr. Wilkinson said, is for mild tropical storms that would help to cool Australian waters.

“If we get a poor monsoon season,” he said, “I think we’re in for a serious bleaching on the Great Barrier Reef.”

Massive Coral Mortality Following Bleaching in Indonesia

Coral bleaching in Indonesia takes a turn for the worst:

The Wildlife Conservation Society has released initial field observations that indicate that a dramatic rise in the surface temperature in Indonesian waters has resulted in a large-scale bleaching event that has devastated coral populations. The initial survey carried out by the team revealed that over 60 percent of corals were bleached.

“Bleaching” — a whitening of corals that occurs when algae living within coral tissues are expelled — is an indication of stress caused by environmental triggers such as sea surface temperature fluctuations. Depending on many factors, bleached coral may recover over time or die.

The event is the result of a rise in sea surface temperatures in the Andaman Sea — an area that includes the coasts of Myanmar, Thailand, the Andaman and Nicobar Island, and northwestern Indonesia. According to the National Oceanic and Atmospheric Administration’s Coral Hotspots website, temperatures in the region peaked in late May of 2010, when the temperature reached 34 degrees Celsius — 4 degrees Celsius higher than long term averages for the area.

“This is a tragedy not only for some of the world’s most biodiverse coral reefs, but also for people in the region, many of whom are extremely impoverished and depend on these reefs for their food and livelihoods,” said WCS-Marine Program Director Dr. Caleb McClennen. “It is another unfortunate reminder that international efforts to curb the causes and effects of climate change must be made if these sensitive ecosystems and the vulnerable human communities around the world that depend on them are to adapt and endure.”

(read more over at Science Daily and the Wildlife Conservation Society)

Human being and fish can coexist peacefully

… or at least that seems to be what Australia’s Opposition leader thinks would happen if he stopped the expansion of marine protected areas in Australian waters:

In a policy aimed at marginal Queensland seats, Mr Abbott said a Coalition government would ”immediately suspend the marine protection process which is threatening the livelihoods of many people in the fishing industry and many people in the tourism industry”.

”All of us want to see appropriate environmental protection, but man and nature have to live together,” Mr Abbott said as he toured the seat of Dawson, in Mackay, which is held by Labor by 2.6 per cent.

Citing “Real action to protect our marine environments and fishing communities” , Mr Abbott wants to balance environmental protection with economic growth by first suspending the marine protected area process. But doesn’t tourism in the Great Barrier Reef Marine Park  generate billions of dollars for the Australian economy annually?

The GBRMP re-zoning that resulted in an increase in strict protection from 4.5% to over 30% was of course intiated under the previous Howard government, and undertaken through a comprehensive research and consultation process. According to Mr Abbott, things have  gone awry since then, although so far the details on this are scanty.

Coalition policy would require consideration of peer reviewed scientific evidence of threats to marine biodiversity before future decisions are made about marine park establishment:

“We would not be interested in just putting lines on maps. If there’s something out there that needs to be protected, if it’s iconic and needs protection, we’d want to see the science and that science would have to be peer-reviewed.”

Fortunately, there is already a lot out there to suggest that the marine environment is under threat, fishing kills fish and that marine parks have benefits for biodiversity and maintaining fish stocks. Conservation planning software used world wide, and developed in Queensland, is used to assist in the creation of marine parks  in a way that seeks to achieve protection for biodiversity while balancing socio-economic objectives.  The science is light years ahead of lines on maps (although, this can be helpful as part of the community consultation process).

It’s encouraging to see the high regard that Mr Abbott places upon peer reviewed science on this issue, so for someone who gets his ‘facts’ about climate change from Heaven + Earth, perhaps a bit of consistency wouldn’t go astray?

Reply to Ridd et al.’s Technical Comment to Science: “Have coral calcification rates slowed in the last twenty years?”

Several denialists have sort to deliberately confuse the readership over the important evidence gathered by De’ath et al. (2009) on slowing coral calcification on the Great Barrier Reef.  Given the recent resurgence in this misinformation, I thought it would be a good idea to post Dr Glenn De’ath, Dr Janice M. Lough and Dr Katharina E. Fabricius’s recent reply  to Dr Peter Ridd’s confused and misleading claims.

The maintenance of coral calcification rates is critical for the future of coral reefs and it is, therefore, important to identify spatial patterns and temporal trends in the rates of coral calcification. Our recent report showed that substantial declines in coral calcification have occurred on the Great Barrier Reef in the last 20 years (De’ath et al., 2009), and similar reports are now emerging from other parts of the world (Tanzil et al., 2009). Ridd et al. here suggest that (1) ontogenetic effects, and (2) the last data points at the end of the recent cores, largely explain the ~14% decline in coral calcification we have shown across the Great Barrier Reef. We believe the assertions of Ridd et al. are erroneous due to: (1) their invalid assumptions about the data, and (2) their inappropriate statistical analyses.

Ontogenetic effects

Ridd et al. argue that we ignored the possibility that ontogentic effects contributed to the reported decline, namely that corals in their youngest years calcify at a faster rate than later in life. However, their main underlying assumption, that age of each short core is given by its number of growth records is wrong. Thus their Fig 2b derived from this assumption, is also wrong. Short cores are ~50 cm long (the length of the coring barrel), whereas the median height of the corals from which the short cores were taken was 1.5 m. The innermost year bands in short cores do not thus reflect early years of the corals’ life in the colonies sampled. Rather, corals were on average ~50 years old (rather than 1 year old, as Ridd et al assume) when the innermost year ring of the short cores was deposited.

In contrast, ontogenetic effects can be accurately assessed in whole colonies where the first years of the corals are preserved. However, Ridd et al. do not include year as a covariate factor, so their analysis is unable to disentangle the two potentially confounded effects of age and temporal trends in environmental conditions.

In the Report, we also investigated ontogenetic effects by comparing calcification in the last 15 years in the life of a coral (the outermost bands) in the 189 colonies collected from 1990 to 2005, and the 139 colonies sampled prior to 1990. We showed that for the cohort prior to 1990, the number of colonies and the number of reefs with increasing and declining rates were approximately equal in number, with 29 of the 56 reefs (51.7%) declining at an average rate of 0.11% yr-1 (SE=0.18%). However, in the 1990–2005 period, 12 of the 13 reefs (92.3%) declined at an average rate of 1.44% yr-1 (SE=0.31%), indicating a strong decline specific to that period, rather than reflecting ontogenetic properties of the outermost annual growth bands in coral skeletons.

End of core data

Ridd et al. argue that the last annual growth layer for each coral of the 2004 and 2005 series are negatively biased estimates of growth due to unspecified problems of measurement and should, therefore, be discarded. Such specific measurement problems are only likely if those corals were measured separately from the remainder. This was not the case as the data are based on the re-measuring and re-dating of all the material using the same methods and the same instrument, and conducted by one person (JML) within the past 5 years.

Ridd et al also argue that the series ending in 2005 (21 corals) did not show a significant decline in 2004, when the series ending in 2004 (containing 77 corals) showed a decline. It is perhaps also worth noting that Ridd et al use the term “significant” on six occasions without any statistical reference or justification. This statement was neither supported by their Fig 1D, nor by any form of statistical analysis or significance tests.

However, we also re-ran the temporal change model excluding the records of corals in 2004-5 (Fig. 1). The decline in calcification from 1990 – 2005 reduces to ~77% of that predicted when all data were included; still a decline of ~11.0%.

Figure 1. Decline in calcification based on all data and with the final years records for 2004-5 removed. The predicted reduction in the current decline for 1990-2005 is reduced from ~14.2% to ~11.0%.

Statistical analyses

Ridd et al. standardise the measurements of individual calcification records, average them for each year, and then analyse the temporal trends using an antiquated smoothing technique (Savitzky-Golay, 1964). There are three major problems with their approach:

(1)   It fails to account for the sampling structure whereby coral colonies are sampled from different reefs in highly variable numbers. There are between 1 and 46 colonies per reef, and the analyses in De’ath et al (2009) accounts for this structure by including random effects of reef and colony nested in reef in their generalized additive models (GAMs). The latter approach also takes into account the correlation across time due to repeated measures on colonies.

(2)   The fitted curves of Ridd et al. have no basis for the selection of smoothness (such procedures did not exist in 1964) and are mostly over-fitted (i.e. they are too wriggly), in particular in the last few years at which time Ridd et al. claim the anomalies exist. For example, the rapid increase in the last year or so of the truncated series is extreme. This contrasts with the failure of their fit to capture a rapid rise in the period 1940-45. All efforts to recapture their fits (no details were provided in Ridd et al.) failed despite using the Savitzky-Golay procedure with a wide range of smoothing.

The analyses of De’ath et al (2009) [SOM] used widely accepted model selection procedures for both random and fixed effect components of the GAMs, within which the smoothness of the temporal profiles was based on cross-validation.

(3)   None of Ridd et al.’s analyses use an inferential statistical model other than linear regression in their Fig. 2., and in that instance no confidence intervals or significance of the regressions are provided. It is also clear from inspection of those plots that strong serial correlation is present, which is not catered for in their analyses.


For the above reasons, we disagree with Ridd et al that the observed declines in coral calcification on the Great Barrier Reef are due to ontogenetic effects in corals, and that the last two years of record should be omitted from the data set. The predicted decline in calcification would drop from ~14.2% to ~11.0% were the last two records omitted; still a major decline. We maintain that this decline in calcification, probably due to synergistic effects of prolonged and repeated temperature stress and ocean acidification in tropical waters, is a real and serious issue for massive Porites on the Great Barrier Reef, and indeed for coral reefs around the world (Tanzil et al., 2009).

Dr Glenn De’ath, Dr Janice M. Lough and Dr Katharina E. Fabricius

Australian Institute of Marine Science, PMB 3, Townsville Qld 4810, Australia.

Good news for the GBR story on ABC’s AM show

Read and hear the full story here.

Report finds some good news for Great Barrier Reef

Sarah Clarke reported this story on Saturday, June 12, 2010 08:15:00

ELIZABETH JACKSON: After facing what appeared to be a gloomy outlook, there’s finally some good news for the Great Barrier Reef.

After a hot summer, and a series of heatwaves last year, scientists say late monsoonal conditions protected much of the coral from a major bleaching event.

But a new study shows mortality in the world’s tropical oceans is increasing, and as bleaching becomes more common, corals simply aren’t getting enough time to recover.

Our environment reporter Sarah Clarke travelled to the Great Barrier Reef for this report.

SARAH CLARKE: 2009 may have been the second warmest year on record, ending the hottest decade in a century, but that heat didn’t translate to ocean temperatures, with a trough delivering last minute respite for much of Australia’s oceans.

Ray Berkelmans is from the Australian Institute of Marine Science.

RAY BERKELMANS: Thankfully, just around Christmas time the active monsoon trough started and that persisted for just about most of the summer.

So together with high cloud cover and strong winds, that kept us from getting warm conditions for most of the summers.

SARAH CLARKE: Those cooler conditions chilled the ocean, protecting much of the Great Barrier Reef. There was some mild bleaching recorded in the southern region but the worst was further north.

Ove Hoegh-Guldberg is from the University of Queensland.

OVE HOEGH-GULDBERG: Right up in northern Australia, you know, in the Torres Strait region you had extremely warm weather for a very long period of time; that pushed sea temperatures above the long term summer maximum by several degrees, and of course that’s what drove bleaching.

SARAH CLARKE: Bleaching occurs when coral’s stress in unusually warmer waters. The worst events in Australia were recorded in 1998 and 2002. Some parts of the Great Barrier Reef have since recovered, but there has been some coral mortality.

And a study by John Bruno from the University of North Carolina now shows between one and two per cent of the world’s tropical corals are being lost each year.

JOHN BRUNO: Well Sarah, we’ve seen coral reefs degrading over the last three or four decades. So we don’t have a lot of data from the late 60s and the early 70s, but we’re quite sure things started really taking off in the early to mid 80s.

So our best guess is that we’ve lot about half of the world’s living coral cover over the last three or four decades.

SARAH CLARKE: That’s combined with new research which suggests that it can take some corals up to 18 months to recover. And as bleaching events become more common, some species won’t have enough time to rebuild.

And that translates to a grim outlook for unique places like the Great Barrier Reef, according to Ove Hoegh-Guldberg from the University of Queensland.

OVE HOEGH-GULDBERG: Now, you can never say from one season to the next that the next year is going to be a mass bleaching event, but what we’re seeing is that that overall risk is increasing over time as the temperature goes up.

You don’t have to be a mathematical genius to work out that, you know, 30 to 40 years from now we’ve lost most of the coral that we have here today, and that’s why a lot of us are very concerned.

Ecological selection drives genetic divergence in a reef building coral

A new study published in the open source journal PLoS ONE (Bongaerts et al 2010) sheds light on the connectivity of corals within and between reef habitats, with some pretty surprising findings. Whilst previous research has identified distinct differences in morphology and genetic structure over small spatial scales, these new findings from the outer-shelf reefs on the Great Barrier Reefs demonstrates that coral populations from directly adjacent habitats can show strong genetic isolation. To test this, the authors used the ubiquitous ‘birds-nest’ coral (Seriatopora hysterix), sampled across a depth gradient of ~30m across two outer-shelf reefs:

Whilst strong genetic structuring of both coral host and the symbiotic algae was observed across the samples taken across a depth profile (2, 6, 27 m depth), high genetic similarity was observed between reefs. This suggests that high levels of gene flow can exist between populations from the same habitats at geographically more distant locations (~20 km).

Scleractinian coral Seriatopora hysterix (the spikey pink / cream looking coral by the post in the second photograph) at 30m depth on Yonge Reef, GBR.

The results from the host and symbiont genetic profiling are pretty convincing:

Such striking differences between relatively shallow environments (e.g. 2 and 6m) implies adaptation of the entire coral (host plus symbiont) to distinct environmental niches. These strong associations to particular reef environments present a compelling case for ecological speciation in reef corals, in that evolutionary processes are occuring in the absence of physical barriers. In this case, corals become so adapted to a specific environmental niche, that selection drives them to become genetically distinct from neighbouring populations. While speciation is understood to be a critical mechanism for diversification on coral reefs, previously it was assumed that physical geographical barriers that isolated populations  (i.e. allopatric speciation) were the primary driving force of diversification in reef corals.

The study not only highlights the complexity of connectivity in reef building corals, but also points to the importance of conserving different reef habitat types in the design of marine parks. In this instance, corals in neighbouring reef systems 20,000m apart were highly similar, whereas corals in adjacent habitats separated by ~25m in depth showed strong differentiation. Given the projected increases in coral bleaching under future climate change scenarios, conservation of deeper reefs (e.g. 27m depth) is of key importance, as these reefs may act as a vital reproductive source for shallower reef areas to recover following disturbance events.


Bongaerts et al (2010) Genetic Divergence across Habitats in the Widespread Coral Seriatopora hystrix and Its Associated Symbiodinium. PLoS ONE 5(5): e10871. doi:10.1371/journal.pone.0010871