‘Not much hope’: Mediterranean coral reefs dying under relentless heat

‘Not much hope’: Mediterranean coral reefs dying under relentless heat

Editor’s note: The oceans have absorbed more than 90% of the excess heat trapped on planet earth due to global warming. Greenhouse gases are also absorbed into the ocean which has increased the acidity of ocean water significantly. Increased heat and acidity makes reproduction and survival more difficult for calcifying organisms such as corals and other marine life. It should be no surprise to anyone that we see coral reefs dying globally. So are plankton populations, fish populations, and countless other species. What is surprising is that efforts to halt and reverse greenhouse gas emissions have thus far been so tepid and ineffective. We must change that.

Article summary:

  • In 2003, a marine heat wave devastated coral reef communities in the Mediterranean Sea, including the reefs in the Scandola Marine Reserve, a protected region off the coast of Corsica.
  • More than 15 years later, the coral reef communities in Scandola still have not recovered.
  • Researchers determined that persistent marine heat waves, which are now happening every year in the Mediterranean, are preventing Scandola’s slow-growing coral reefs from recuperating.
  • Human-induced climate change is the culprit; persistent rising temperatures in the ocean have normalized marine heat waves, not only in the Mediterranean, but in the global oceans.

For years, Joaquim Garrabou donned scuba gear and dove into the waters of the Scandola Marine Reserve in Corsica to find a paradise. Twenty meters (66 feet) beneath the surface, there were reef walls draped with soft red coral (Corallium rubrum) and red gorgonian sea-whips (Paramuricea clavata), all swarming with fish and other sea creatures. But in 2003, a marine heat wave hit Scandola, leading to the death of many coral reefs. More than 15 years later, the reefs have still not recovered.

Now when Garrabou dives at Scandola, he’s greeted by the skeletons of once-thriving corals.

“It’s like seeing someone who is ill, who has a disease that you cannot find the solution for,” Garrabou told Mongabay in a video interview. “You hope that someday there will be a [solution] but you see that there’s not much hope.”

After the 2003 marine heat wave, Garrabou and colleagues began monitoring Scandola’s coral reefs to track their recovery. But after accumulating reef survey data and temperature data over many years, they eventually realized they were actually tracking the reefs’ collapse. The results of their long-term study were recently published in Proceedings of the Royal Society B.

“We knew something bad was happening to the corals around the world, but we weren’t expecting a collapse in all of the populations that we studied,” study lead author Daniel Gómez-Gras, a marine ecologist at the Institut de Ciències del Mar in Barcelona, told Mongabay in a video interview. “The point of tracking these populations for such a long time was to show recovery in the long term because we expected that the populations — maybe not in five years, but in 15, 20 years — [would be] able to recover. However, we saw a collapse.”

reefs dying, illustrative picture of healthy reef
A researcher monitoring a red coral population in the Mediterranean. Image by Medrecover.

‘We don’t call it bleaching’

The data showed that marine heat waves were happening every year in different parts of the Mediterranean between 2003 and 2018. For 12 of those years, the water temperature at a depth of 20 m reached more than 23° Celsius (73.4° Fahrenheit), which is considered a sublethal threshold for corals. And for four of those years — 2009, 2016, 2017 and 2018 — temperatures at that depth breached the lethal threshold for corals at 25°C (77°F).

The researchers found that the ceaseless heat wasn’t allowing these slow-growing coral reefs to recover.

​​“Frankly, I never thought that I would be seeing it,” Garrabou said. “And it’s happening really fast.”

Soft coral species in the Mediterranean don’t “bleach” the way that tropical corals do, Gómez-Gras said. That’s because Mediterranean corals don’t have a symbiotic relationship with zooxanthellae, the algae that tropical corals expel when they experience heat stress.

“We don’t call it bleaching here in the Mediterranean for these coral species, since they don’t bleach,” he said. “They directly die with a loss of tissue and skeletons being exposed.”

While the results of the study are relevant to many coral communities across the Mediterranean, the researchers chose to focus their study on Scandola because the area had been established as a marine protected area (MPA) in 1975, and had been relatively free from other human pressures such as fishing and pollution. This helped them eliminate other possibilities for the coral reef population collapses and to pinpoint marine heat waves as the reason for their demise.

Researchers used to think that deeper reef communities might shelter coral species from heat stress. But it’s becoming increasingly clear that this isn’t the case, not only in the Mediterranean, but in other parts of the world, including coral reef sites in the Pacific.

“We are witnessing that if you go deeper, [there is still] impact,” Garrabou said.

Maps showing the location of Scandola within the Mediterranean, as well as the location, species and depth of the five monitored populations within Scandola MPA. The graph shows the number of marine heat waves that occurred between 1982 and 2018, and severity of each event. Image by Gómez-Gras et al (2022).

Raised temperatures

Human-induced climate change is responsible for the heating of the oceans — and it’s becoming hotter and hotter in the water. According to another study, the global oceans have broken a heat record for the sixth year in a row. As the oceans warm, heat penetrates downward — and this heating trend will continue even if emissions stop tomorrow, Kevin Trenberth, co-author of this separate study, told Mongabay in January.

A related study also found that marine heat waves have become the new normal for the global oceans as climate change rapidly transforms our world.

The Mediterranean may be feeling the impacts of climate change even more intensely than other parts of the world. A report published last year by WWF found that the Mediterranean was warming 20% faster than the rest of the world’s oceans.

Gómez-Gras said the accelerated warming in the Mediterranean has partly to do with its semi-enclosed shape. While this is unique to the region, he added that the Mediterranean shows what will happen in other parts of the ocean due to climate change.

“Marine heat waves are becoming the new normal in the Mediterranean Sea,” Gómez-Gras said. “So you can guess that in the future, it can become the new normal [elsewhere] in the world.”

Georgios Tsounis, a marine biologist at California State University, whose work was based in the Mediterranean for 11 years, but who was not involved in this research, praised the new study in Proceedings of the Royal Society B for its “valuable approach.”

“We need more long-term demographic studies such as this one to better understand where our environment is heading in the future,” Tsounis told Mongabay in an email.

While the study is focused on the soft coral communities of the Mediterranean, Tsounis said the research can help us understand how other coral communities “may or may not recover from repeated stress over a period of 15 years.”

“We are seeing coral mortality in other parts of the world as well,” he said. “The tropical coral reefs make sad headlines every year. But in the tropics we are mainly concerned with reef-building hard corals (as opposed to the soft corals in this Mediterranean study). The temperature range and entire cause-effect mechanism differ between these two examples. What is common to most of these scenarios is that the corals have adapted to a narrow set of environmental conditions, such as temperature, over a long period of time, and are sensitive to changing climate.”

A red coral population with dead colonies after a marine heat wave in 2016. Image by Olivier Bianchimani.

Seeking refuge

The researchers said they are searching the Mediterranean for “refugia,” places that offer coral reefs protection from thermal stress. One possible place could be the waters off the coast of the Calanques near Marseille, France, which seems to get enough cold water to protect its corals, Garrabou said. That said, the coral reef communities here experienced mass die-offs during marine heat waves in both 1999 and 2003. But since then, the region hasn’t had any major warming, and the corals have been able to slowly recover, he said.

While there are currently many places of refugia for coral communities across the world, a new study found that most of these places will disappear once the world reaches 1.5°C (2.7°F) of warming above pre-industrial levels, which is likely to happen within the next decade.

But it’s not just climate change placing pressure on the Mediterranean — fishing and pollution are additional stressors to the region. Because of this, Garrabou said it’s important to establish MPAs with strict protective measures to enhance the resilience of coral reef communities.

Currently, there are more than 1,200 MPAs in the Mediterranean, but only about 0.02% of the area they cover is closed to fishing year-round.

While the future looks grim for coral reefs, Garrabou said he feels hopeful about the momentum that’s building for the establishment of MPAs, especially with global efforts to protect 30% of the world’s oceans by 2030.

“When we provide the right conditions and the right tools, nature can be really generous and nature has demonstrated that it can bounce back,” he said.

But he said that MPAs need to be urgently established for the oceans to reap their benefits. “It has to happen,” he said, “and it has to happen fast.”


Bongaerts, P., Ridgway, T., Sampayo, E. M., & Hoegh-Guldberg, O. (2010). Assessing the ‘deep reef refugia’ hypothesis: Focus on Caribbean reefs. Coral Reefs, 29(2), 309-327. doi:10.1007/s00338-009-0581-x

Cheng, L., Abraham, J., Trenberth, K. E., Fasullo, J., Boyer, T., Mann, M. E., … Reagan, J. (2022). Another record: Ocean warming continues through 2021 despite La Niña conditions. Advances in Atmospheric Sciences. doi:10.1007/s00376-022-1461-3

Dixon, A. M., Forster, P. M., Heron, S. F., Stoner, A. M., & Beger, M. (2022). Future loss of local-scale thermal refugia in coral reef ecosystems. PLOS Climate, 1(2), e0000004. doi:10.1371/journal.pclm.0000004

Gómez-Gras, D., Linares, C., López-Sanz, A., Amate, R., Ledoux, J. B., Bensoussan, N., … Garrabou, J. (2021). Population collapse of habitat-forming species in the Mediterranean: A long-term study of gorgonian populations affected by recurrent marine heatwaves. Proceedings of the Royal Society B: Biological Sciences, 288(1965). doi:10.1098/rspb.2021.2384

Jeffries, E., & Campogianni, S. (2021). The climate change effect in the Mediterranean. Six stories from an overheating sea. Retrieved from WWF website: https://www.wwf.de/fileadmin/fm-wwf/Publikationen-PDF/Meere/WWF-Report-The-Climate-Change-Effect-in-the-Mediterranean-2021.pdf

Tanaka, K. R., & Van Houtan, K. S. (2022). The recent normalization of historical marine heat extremes. PLOS CLIMATE. doi:10.1371/journal.pclm.0000007

Banner image: A red gorgonian coral (Paramuricea clavata) partially dead due to a marine heatwave. The lefthand side is still alive, while the righthand side is dead and the skeleton is exposed. Image by Eneko Aspillaga.

This article first appeared in Mongabay.

New study finds 80% of Caribbean coral reefs destroyed since 1960s

By Fiona Harvey / The Guardian

A major survey of the coral reefs of the Caribbean is expected to reveal the extent to which one of the world’s biggest and most important reserves of coral has been degraded by climate change, pollution, overfishing and degradation.

The Catlin scientific survey will undertake the most comprehensive survey yet of the state of the region’s reefs, starting in Belize and moving on to Mexico, Anguilla, Barbuda, St Lucia, Turks & Caicos, Florida and Bermuda.

The Catlin scientists said the state of the regions’ reefs would act as an early warning of problems besetting all of the world’s coral. As much as 80% of Caribbean coral is reckoned to have been lost in recent years, but the survey should give a more accurate picture of where the losses have had most effect and on the causes.

Loss of reefs is also a serious economic problem in the Caribbean, where large populations depend on fishing and tourism. Coral reefs provide a vital home for marine creatures, acting as a nursery for fish and a food resource for higher food chain predators such as sharks and whales.

Stephen Catlin, chief executive of the Catlin Group, said: “It is not only important that scientists have access to this valuable data, but companies such as ours must understand the impact that significant changes to our environment will have on local economies.”

Globally, coral reefs are under threat. The future of the Great Barrier Reef in Australia is in doubt as mining and energy companies want to forge a shipping lane through it to form a more direct link with their export markets.

Warming seas owing to climate change can lead to coral being “bleached” – a state where the tiny polyps that build the reefs die off. The US government’s National Oceanic and Atmospheric Administration predicts increasing frequency and severity of mass bleaching events as global warming takes effect.

Richard Vevers, director of the project, told the Guardian that one important role of the new survey would be to describe a new “baseline” to establish how far such problems have taken their toll to date, which will enable future scientists to judge how degradation – or conservation – progresses.

He said the team of scientists would also probe the underlying reasons for such degradation, with a view to informing conservation efforts.

The team will use satellite data as well as direct observations to assess the reefs. As part of the survey, they will develop software that marine scientists can apply to other reefs around the world. A new camera has been constructed to assist their efforts.

Vevers said: “The Caribbean was chosen to launch the global mission because it is at the frontline of risk. Over the last 50 years 80% of the corals have been lost due mainly coastal development and pollution. They now are also threatened by invasive species, global warming and the early effects of ocean acidification — it’s the perfect storm.”

From The Guardian: http://www.theguardian.com/environment/2013/aug/01/caribbean-coral-reef-loss

30 years of industrialization in China has destroyed at least 80% of coral reefs

By Agence France-Presse

China’s economic boom has seen its coral reefs shrink by at least 80 percent over the past 30 years, according to a joint Australian study, with researchers describing “grim” levels of damage and loss.

Scientists from the Australian Research Council Centre of Excellence for Coral Reef Studies and the South China Sea Institute of Oceanology said their survey of mainland China and South China Sea reefs showed alarming degradation.

“We found that coral abundance has declined by at least 80 percent over the past 30 years on coastal fringing reefs along the Chinese mainland and adjoining Hainan Island,” said the study, published in the latest edition of the journal Conservation Biology.

“On offshore atolls and archipelagos claimed by six countries in the South China Sea, coral cover has declined from an average of greater than 60 percent to around 20 percent within the past 10-15 years,” it added.

Coastal development, pollution and overfishing linked to the Asian giant’s aggressive economic expansion were the major drivers, the authors said, describing a “grim picture of decline, degradation and destruction”.

“China’s ongoing economic expansion has exacerbated many wicked environmental problems, including widespread habitat loss due to coastal development, unsustainable levels of fishing, and pollution,” the study said.

Coral loss in the South China Sea — where reefs stretch across some 30,000 square kilometres (12,000 square miles) — was compounded by poor governance stemming from competing territorial claims.

Some marine parks aimed at conservation had been established but study author Terry Hughes said they were too small and too far apart to arrest the decline in coral cover.

“The window of opportunity to recover the reefs of the South China Sea is closing rapidly, given the state of degradation revealed in this study,” he said.

The South China Sea is strategically significant, home to some of the world’s most important shipping lanes and believed to be rich in resources.

China claims most of the sea including waters close to the shores of its neighbours. Rival claimants include Brunei, Malaysia, the Philippines and Vietnam, and tensions over the issue have flared in recent years.

From The Raw Story: http://www.rawstory.com/rs/2012/12/26/study-coral-reefs-decimated-by-chinese-economic-boom/

Study finds that 70% of coral reefs will collapse even if warming is kept to 2°C

Study finds that 70% of coral reefs will collapse even if warming is kept to 2°C

By Inter-Press Service

Limiting climate change to two degrees C won’t save most coral reefs, according to new, state-of-the-art research.

About 70 percent of corals are projected to suffer from long-term degradation by 2030 with two degrees C of warming, the first comprehensive global survey reported Sunday in the journal Nature Climate Change.

The planet will get far hotter than two degrees C based on current commitments by countries to reduce their greenhouse gas emissions, mainly from burning oil, gas and coal. Humanity is on course to heat up the atmosphere an average of three and even four degrees C, according to the Climate Action Tracker, an international scientific monitor. Those temperature levels are what most scientists consider “catastrophic”.

Global temperatures have risen an average of about 0.8C so far and already melted much of the Arctic and generated costly extreme weather events around the planet. Keeping that global average increase below two degrees is only a matter of “political will” not technology, said Bill Hare, director of Climate Analytics, one of the partners in the Climate Action Tracker.

If humanity wants to keep at least half of the remaining coral reefs, then global temperatures cannot rise to 1.5C. “Limiting global warming to 2 C is unlikely to save most coral reefs,” the paper reports.

“We must realise what is at stake as global temperatures rise,” said co-author Malte Meinshausen of School of Earth Sciences at the University of Melbourne.

“Countries must be as ambitious as possible in their emission reductions to give corals a chance,” Meinshausen told IPS.

Coral reefs are considered by many to be one of the life-support systems essential for human survival. For more than 2.6 billion people, seafood is the main source of protein. Corals act as the nurseries and habitat for many fish species, and are vital for up to 33 percent of all ocean species, according to the World Conservation Union (IUCN).

Reefs also provide vital shoreline protection from storms. Without reefs, for example, Belize would suffer 240 million dollars in damage from storms, according to one estimate.

This study used the very latest climate models and applied them to growing science about the impacts of rising temperatures and acidification levels projected in the decades to come, said co-author Simon Donner, a marine biologist and climatologist at the University of British Columbia.

The increasing ocean acid conditions appear to be reducing coral’s thermal tolerance, Donner said in an interview. Tropical corals have a narrow water temperature range in which they thrive. When water temperature rises only two or three degrees, they “bleach” or turn white.

Corals can survive this, but if the heat stress persists long enough – weeks instead of days – the corals can die in great numbers, as they did in 1998 when 16 percent of the world’s tropical corals died.

Emissions of greenhouse gases are not only warming the oceans, they have also made them 30 percent more acidic. The oceans and the atmosphere are intimately connected. When CO2 is released into the atmosphere from burning fossil fuels, some of that extra CO2 combines with carbonate ions in seawater, forming carbonic acid. This level of change in ocean chemistry has not happened in millions of years and is beginning to dissolve reefs.

Some corals will undoubtedly survive and some will adapt to the new conditions, although the changes are far more rapid than anything corals have ever experienced, said Donner.

“The bottom line is that humanity will lose the services that corals have provided for thousands of years,” he said.

Even at 1.5 C degrees of warming, only about half corals are likely to survive, the study found. That adds scientific weight to the small island nations’ and other countries’ call for a global target of 1.5 C, Donner said.

Every nation in the world officially agreed to keep global temperature increase below two degrees C at a U.N. climate meeting in Cancun, Mexico in 2010. An alliance of small islands and African countries had lobbied for the global target of less than 1.5 C due to the damages they are expected to suffer if temperatures rise above that mark.

Emissions must begin to decline this decade for either target so it is pointless to debate these targets right now, says Meinshausen. Once emissions are in significant decline, then how fast and how deep those cuts will have relevance for the final target, he said.

“I fear we’re going to miss our only chance to peak emissions this decade,” he said.

Read more from Inter-Press Service: http://www.ipsnews.net/2012/09/deeper-co2-cuts-needed-to-save-corals/

Ocean acidification poses dire threat to coral reefs

Ocean acidification poses dire threat to coral reefs

By the Associated Press

Oceans’ rising acid levels have emerged as one of the biggest threats to coral reefs, acting as the “osteoporosis of the sea” and threatening everything from food security to tourism to livelihoods, the head of a US scientific agency said Monday.

The speed by which the oceans’ acid levels has risen caught scientists off-guard, with the problem now considered to be climate change’s “equally evil twin,” National Oceanic and Atmospheric Administration (NOAA) chief Jane Lubchenco told The Associated Press.

“We’ve got sort of the perfect storm of stressors from multiple places really hammering reefs around the world,” said Lubchenco, who was in Australia to speak at the International Coral Reef Symposium in the northeast city of Cairns, near the Great Barrier Reef. “It’s a very serious situation.”

Oceans absorb excess carbon dioxide in the atmosphere, leading to an increase in acidity. Scientists are worried about how that increase will affect sea life, particularly reefs, as higher acid levels make it tough for coral skeletons to form. Lubchenco likened ocean acidification to osteoporosis a bone-thinning disease because researchers are concerned it will lead to the deterioration of reefs.

Scientists initially assumed that the carbon dioxide absorbed by the water would be sufficiently diluted as the oceans mixed shallow and deeper waters. But most of the carbon dioxide and the subsequent chemical changes are being concentrated in surface waters, Lubchenco said.

“And those surface waters are changing much more rapidly than initial calculations have suggested,” she said. “It’s yet another reason to be very seriously concerned about the amount of carbon dioxide that is in the atmosphere now and the additional amount we continue to put out.”