Coral reefs and climate change

Mica Prazak, Milan Ilnyckyj, and Sasha Ilnyckyj

While the Arctic is the most climatically vulnerable human-inhabited environment, coral reefs will probably see the most comprehensive destruction in coming decades. According to the IPCC, it is highly likely that they will succumb to a combination of heat and oceanic acidification as temperatures rise in response to greenhouse gas emissions. It is estimated that the last 25 years have seen the loss of 30% of warm-water coral cover. The worst summers so far for coral bleaching have been 1998 and 2002: in which 42% and 54% of all reefs worldwide were affected. As much as 80% of Caribbean coral may already have died.

Coral bleaching occurs when the zooxanthella algae that live in coral tissues die. The report of Working Group II of the IPCC highlights high surface temperatures as “almost certain to increase the frequency and intensity of mass coral bleaching events.” Throughout the Third and Fourth Assessment Reports, coral reefs are highlighted as being especially vulnerable to climatic change, with low adaptive capability.

Oceanic acidification reduces the calcifying ability of corals, by making it more difficult for them to extract calcium from seawater. In cases of extreme acidity, existing structures could begin to dissolve. According to the IPCC “the progressive acidification of oceans is expected to have negative impacts on marine shellforming organisms.” Studies have demonstrated that projected future ocean acidity will reduce coral calcification and weaken coral skeletons.

The Fourth Assessment Report projects that most corals will be bleached by a temperature rise of 1 to 3°C, with increasing coral mortality at higher levels of temperature increase. Between 2.5 and 3.5°C above the pre-industrial mean temperature, a summary table in the WGII report predicts simply “Corals extinct, reefs overgrown by algae.” It warns further that: “It is important to note that these impacts do not take account of ancillary stresses on species due to over-harvesting, habitat destruction, landscape fragmentation, alien species invasions… or pollution.” Given the low probability of keeping further temperature increases below 2°C – even with the advent of relatively stringent new international obligations – it is fair to say that most of the world’s coral is doomed to die. That, in turn, will undermine much of the basis of coral reef ecosystems. This is a further burden to some small island states, as coral reefs can be the habitat for important fish stocks. Reefs are also the most diverse marine ecosystems: home to about 25% of all marine species.

One way to interpret the news is this: if you have always dreamed of SCUBA diving in the natural splendour of a coral reef, make sure you do it fairly soon. Your children might not be able to do it at all. To quote the IPCC once more: “Annual or bi-annual exceedance of bleaching thresholds is projected at the majority of reefs worldwide by 2030 to 2050.”

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

31 thoughts on “Coral reefs and climate change”

  1. The fate of coral
    Not just a pretty polyp

    Mar 22nd 2007
    From The Economist print edition

    IF YOU thought coral was just a basic form of rather pretty underwater life, think again. The diminutive reef-builders gave us oxygen to breathe, cooled the atmosphere down to a clement level and went on to build the only biological structure that is visible from space—the Great Barrier Reef.

  2. God bless the primordial cyanobacteria, on this holiest of days.

    “And the Lord said, ‘Let there be a photosynthetic bacterium of the class Coccogoneae or Hormogoneae, generally blue-green in color and in some species capable of nitrogen fixation.’, and it was good.”

  3. it is fair to say that most of the world’s coral is doomed to die

    Wow. Talk about being responsible stewards of the earth…

  4. This is really sad. Coral reefs have probably existed for millions of years, and we wiped them out in a few hundred.

  5. In tropical shallow waters, a temperature increase of up to
    only 3° C by 2100 may result in annual or bi-annual bleaching
    events of coral reefs from 2030–2050. Even the most optimistic
    scenarios project annual bleaching in 80–100% of the World’s
    coral reefs by 2080. This is likely to result in severe damage
    and wide-spread death of corals around the World, particularly
    in the Western Pacific, but also in the Indian Ocean, the Persian
    Gulf and the Middle East and in the Caribbean.

  6. As CO2 concentrations in the atmosphere increase so does
    ocean assimilation, which, in turn, results in sea water becoming
    more acidic. This will likely result in a reduction in the area
    covered and possible loss of cold-water coral reefs, especially
    at higher latitudes. Besides cold-water corals, ocean acidification
    will reduce the biocalcification of other shell-forming organisms
    such as calcareous phytoplankton which may in turn
    impact the marine food chain up to higher trophic levels.

  7. Key coral reefs ‘could disappear’

    By Lucy Williamson
    BBC News, Manado, Indonesia

    The world’s most important coral region is in danger of being wiped out by the end of this century unless fast action is taken, says a new report.

    The international conservation group WWF warns that 40% of reefs in the Coral Triangle have already been lost.

    The area is shared between Indonesia and five other South East Asian nations and is thought to contain 75% of the world’s coral species.

    It is likened to the Amazon rainforest in terms of its biodiversity.

  8. Climate targets ‘will kill coral’
    By Richard Black
    Environment correspondent, BBC News website

    Current climate targets are not enough to save the world’s coral reefs – and policymakers urgently need to consider the economic benefits they bring.

    Those are two of the conclusions from a UN-backed project aiming to quantify the financial costs of damaging nature.

    Studies suggest that reefs are worth more than $100bn (£60bn) annually, but are already being damaged by rising temperatures and more acidic oceans.

    The study puts the cost of forest loss at $2-5 trillion annually.

    Looking ahead to December’s UN climate conference in Copenhagen, study leader Pavan Sukhdev said it was vital that policymakers realised that safeguarding the natural world was a cost-effective way of protecting societies against the impacts of rising greenhouse gas levels.

  9. “In time, it sent me searching for two other pieces of esoteric but existentially critical science news that emerged in 2008 and quickly vanished in the churning media sea of burst housing bubbles and flailing banks. The first was a concise policy paper released in August and signed by fourteen of the world’s top ocean researchers — Charlie Veron among them — under the title The Honolulu Declaration on Ocean Acidification and Reef Management. Their statement noted the imminent onset of levels of ocean acidity not seen in “tens of millions of years,” which would “compromise the long-term viability of coral reef ecosystems.” The crisis was phrased more bluntly in the accompanying press release: “In July 2008, scientists at the International Coral Reef Symposium in Florida declared acidification as the largest and most significant threat that oceans face today and conveyed that coral reefs will be unable to survive the projected increases in ocean acidification.””

  10. Diversity of corals, algae in warm Indian Ocean suggests resilience to future global warming
    Published: Tuesday, February 16, 2010 – 11:59 in Earth & Climate

    Penn State researchers and their international collaborators have discovered a diversity of corals harboring unusual species of symbiotic algae in the warm waters of the Andaman Sea in the northeastern Indian Ocean. “The existence of so many novel coral symbioses thriving in a place that is too warm for most corals gives us hope that coral reefs and the ecosystems they support may persist — at least in some places — in the face of global warming,” said the team’s leader, Penn State Assistant Professor of Biology Todd LaJeunesse. According to LaJeunesse, the comprehensiveness of the team’s survey, which also included analysis of the corals and symbiotic algae living in the cooler western Indian Ocean and Great Barrier Reef area of Australia, is unparalleled by any other study.

  11. World’s coral reefs could disintegrate by 2100

    Researchers at Carnegie Institution say corals are being overwhelmed by rising carbon dioxide in the atmosphere

    The world’s coral reefs will begin to disintegrate before the end of the century as rising carbon dioxide levels in the atmosphere make the oceans more acidic, scientists warn.

    The research points to a looming transition in the health of coral ecosystems during which the ability of reefs to grow is overwhelmed by the rate at which they are dissolving.

    More than 9,000 coral reefs around the world are predicted to disintegrate when atmospheric carbon dioxide levels reach 560 parts per million.

    The amount of carbon dioxide in the atmosphere today stands at around 388ppm, but is expected to reach 560ppm by the end of this century.

    Coral reefs are at the heart of some of the most biodiverse marine ecosystems in the world. They are home to more than 4,000 species of fish and provide spawning, refuge and feeding areas for marine life such as crabs, starfish and sea turtles.

    “These ecosystems which harbour the highest diversity of marine life in the oceans may be severely reduced within less than 100 years,” said Dr Jacob Silverman of the Carnegie Institution in Stanford University, California.

  12. Scientists put reef in deep freeze; Coral suspended in liquid nitrogen in effort to preserve Australian treasure

    The arid plains fringing Australia’s desert centre are more suited to camels than blooms of coral, but here, hundreds of kilometres from the coast, a piece of the Great Barrier Reef has been put on ice.

    Suspended in a liquid nitrogen chamber of -196 C, the 70 billion sperm and 22 billion coral embryos are part of an ambitious Australian project to preserve and perhaps one day regenerate the world-famous reef.

    “We know the Great Barrier Reef is in deep, deep trouble because of a number of different things – global threats including climate change and acidification of waters as well as the warming of waters,” said the project’s director, Rebecca Spindler. “We will never have as much genetic diversity again as we do right now on the reef, this is our last opportunity to save as much as we possibly can.”

    Spindler’s team is working with Hawaii-based Mary Hagedorn from the Smithsonian Institution to collect and freeze samples from the World Heritage-listed reef, a sprawling and vivid natural wonder visible from space.

    In order to maximize the amount of reproductive cells – gametes – collected, the team cut away sections of the reef and took them back to land-based tanks to spawn, an event that only occurs for three days a year.

  13. Mesoamerican Coral Reef on the Way to Becoming a Marine Desert

    GUATEMALA CITY, Mar 7 (IPS) – Scientific studies show that global warming is causing irreversible damage to the Mesoamerican Barrier Reef System, the world�s second largest coral reef, yet efforts to protect this biologically and economically vital ecosystem remain insufficient.Rising sea temperatures provoke an increase in “bleaching” or loss of pigmentation in coral reefs.

    “This basically means the death of the coral due to the disappearance of the zooxanthellae algae that live in symbiosis with these ecosystems,” expert Juan Carlos Villagrán from the Guatemalan branch of The Nature Conservancy (TNC) told Tierramérica*.

    Coral gets its colors from the zooxanthellae that cover the polyps – the tiny individual animals that make up a piece of coral – and produce sugars and amino acids to feed them. In exchange, the algae get a safe place to live with just enough light to grow through photosynthesis.

  14. The researchers examined more than 35,000 coral colonies along Australia’s Great Barrier Reef. The sites studied were up to 1,081 miles (1,740 kilometers) apart.

    “We chose the iconic Great Barrier Reef as our natural laboratory because water temperature varies by 8 to 9 degrees Celsius (14.4 to 16.2 degrees Fahrenheit) along its full length from summer to winter, and because there are wide local variations in pH [a measure of acidity],” Hughes said. “Its regional-scale natural gradients encompass the sorts of conditions that will apply several decades from now under business-as-usual greenhouse gas emissions.”

    The results revealed “surprisingly flexible” assemblies of corals along the reef and in different environments within the reef, the researchers reported Thursday (April 12) in the journal Current Biology. For example, on the crests of the reef, nine of the 12 major scientific groupings found varied widely from region to region. Species colonizing reef crests likewise varied from reef slopes.

    Earlier research has shown that corals’ survival could depend on the presence of warm-water genes. Some solitary coral can survive in extremely acidic submarine springs, but these coral look very different from the iconic reef-building types known today.

    The ultimate effects of climate change could mean that the reefs of the future look very different than the ones of today. For example, if branching corals were replaced by moundlike corals, fish would have fewer nooks and crannies for shelter, Hughes said. But the findings also indicate the reefs will ultimately survive climate change in some form — if something else doesn’t kill them off first.


    Cited research:
    Assembly Rules of Reef Corals Are Flexible along a Steep Climatic Gradient
    Current Biology, Available online 12 April 2012
    Terry P. Hughes, Andrew H. Baird, Elizabeth A. Dinsdale, Natalie A. Moltschaniwskyj, Morgan S. Pratchett, Jason E. Tanner, Bette L. Willis
    Abstract & highlights:

    Can coral cope with climate change?
    Journal name: Nature
    Volume: 484, Page: 290
    Date published: (19 April 2012)
    DOI: doi:10.1038/484290a
    Published online 18 April 2012

    Climate change is likely to alter the species composition of coral reefs, rather than wipe out entire reef ecosystems.

    Terry Hughes at James Cook University in Townsville, Australia, and his team sampled 132 sites along the full length of the Great Barrier Reef (pictured), spanning 13° of latitude and a range of sea surface temperatures. Of the 12 coral taxa sampled, 11 showed significant differences in abundance across the reef, regardless of how susceptible they were to thermal stress and bleaching. These differences in abundance did not follow changes in latitude or temperature.
    This flexibility may enable coral reefs to continue functioning as the environment alters with climate change.

  15. Skeletal trade-offs in coralline algae in response to ocean acidification

    Ocean acidification is changing the marine environment, with potentially serious consequences for many organisms. Much of our understanding of ocean acidification effects comes from laboratory experiments, which demonstrate physiological responses over relatively short timescales. Observational studies and, more recently, experimental studies in natural systems suggest that ocean acidification will alter the structure of seaweed communities. Here, we provide a mechanistic understanding of altered competitive dynamics among a group of seaweeds, the crustose coralline algae (CCA). We compare CCA from historical experiments (1981–1997) with specimens from recent, identical experiments (2012) to describe morphological changes over this time period, which coincides with acidification of seawater in the Northeastern Pacific. Traditionally thick species decreased in thickness by a factor of 2.0–2.3, but did not experience a change in internal skeletal metrics. In contrast, traditionally thin species remained approximately the same thickness but reduced their total carbonate tissue by making thinner inter-filament cell walls. These changes represent alternative mechanisms for the reduction of calcium carbonate production in CCA and suggest energetic trade-offs related to the cost of building and maintaining a calcium carbonate skeleton as pH declines. Our classification of stress response by morphological type may be generalizable to CCA at other sites, as well as to other calcifying organisms with species-specific differences in morphological types.

  16. The outlook for coral is dire. The Intergovernmental Panel on Climate Change, a un body, predicted last month that a rise in global temperatures of 1.5ºC relative to pre-industrial times would probably kill 70-90% of the world’s coral reefs. Given that the planet has already warmed by about 1ºC, the countdown for corals has begun. But the diversity of coral species and the variety of habitats in which they thrive mean that they will not disappear in a uniform way. Understanding why reefs like Black Rock survive and recover from overheating is essential to conservation efforts.

  17. It turns out that high temperatures were wreaking havoc under the water as well. This month comes news that exceptionally warm seas have led the Great Barrier Reef, the world’s biggest coral system, to suffer its third mass bleaching in five years. The bush and the reef, both ravaged on a gargantuan scale: Australians almost define themselves by these two ecosystems, which once seemed boundless.

    Coral bleaching takes place when sea temperatures spike, causing the coral polyps that make up reefs to eject the algae that generate their food via photosynthesis. Without the pigmented algae, coral soon dies, leaving the intricate colonies a ghostly white. Reefs can recover from occasional bleachings: the fastest-growing corals regenerate in a decade or so. But mass bleachings on the Great Barrier Reef are becoming ever more frequent. The first occurred only in 1998. There have since been four more: in 2002, 2016, 2017 and now this year. They have become so common that the Bureau of Meteorology issues forecasts for them.

    The latest bleaching is not as severe as the worst one, in 2016, when about half of the northern part of the 2,300km-long reef died. But the run of recent bleachings had already killed off relatively heat-intolerant coral species. What is striking this year, says Terry Hughes of James Cook University in Queensland, who led a recent aerial survey of the reef, is that for the first time the bleaching extended to the southern part of the reef. There, closer to the pole, waters should be cooler. Not this year. February saw the highest sea-surface temperatures across the reef since monitoring began 120 years ago.

  18. Those in peril in the sea

    A mix of natural resilience and human ingenuity can save endangered ecosystems

    These are the rainforests of the ocean. They exist on vast scales: half a trillion corals line the Pacific from Indonesia to French Polynesia, roughly the same as the number of trees that fill the Amazon. They are equally important havens of biodiversity. Rainforests cover 18% of the land’s surface and offer a home to more than half its vertebrate species. Reefs occupy 0.1% of the oceans and host a quarter of marine species.

    And corals are useful to people, too. Without the protection which reefs afford from crashing waves, low-lying islands such as the Maldives would have flooded long ago, and a billion people would lose food or income. One team of economists has estimated that coral’s global ecosystem services are worth up to $10trn a year.

    Without carbon mitigation and decline in local, coral-killing pollution, even resistant corals will not survive the century. Sceptics doubt humanity will get its act together in time to make much difference.

    But when entire ecosystems are facing destruction, the cost of doing nothing is too great to bear. For coral reefs, at least, if any are to survive at all, it will be those that humans have re-engineered to handle the future.

  19. Corals are threatened by global warming

    A bit of pre-emptive tinkering by people might help to save them

    And the world is getting warmer. As a consequence, the amount of coral in it has fallen since 1980 by between 30% and 50%.

    Locally, things can be yet more dramatic. In just three years (between 2015 and 2018) Australia’s Great Barrier Reef lost more than 30% of its corals to death-by-bleaching.

    These losses affect more than just tourists. Coral reefs are important parts of the world’s ecology. They host a third of multicellular marine species, including many commercially important fish. They also provide free coastal defences. Cities such as Cancún, Honolulu and Miami rely on them to keep the waves at bay. According to a study published in 2014 by Robert Costanza, an economist at University College, London, such benefits have a value of up to $10trn a year. Preserving reefs is thus of practical as well as aesthetic importance. So something needs to be done to stop heat-induced bleaching.

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