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All About: Coral Reefs

  • Story Highlights
  • Coral reefs are home to 25 percent of the world's marine fish species
  • UNEP: About 30 percent of world's coral reefs are already damaged
  • Coral reefs have been used to treat cancers, HIV, and cardiovascular diseases
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By Rachel Oliver
For CNN
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(CNN) -- Coral reefs are often referred to as the canaries of the ocean -- because, like the canary in a mine, they give an indicator of the dangers that lie ahead. Judging by the state of coral reefs these days, if you happen to be a fish, it's not looking good for you.

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Coral reefs in the Indo-Pacific region are now being destroyed at a rate of 1 percent a year.

Coral reefs are home to 25 percent of the world's marine fish species, and cover 1 percent of the Earth's surface, making them the largest single living structure on Earth. They are now also one of the most endangered: As of the end of this year, for the first time in history coral reefs have been included on the World Conservation Union's Red List of Threatened Species.

According to the United Nations Environment Program, or UNEP, around 30 percent of the world's coral reefs are already damaged, some irreparably. At the present rate of destruction, by the year 2050, a breathtaking 70 percent of the world's reefs will have disappeared, according to the Nature Conservancy.

Coral reefs in the Indo-Pacific region -- where 75 percent of the world's reefs live -- are now being destroyed at a rate of 1 percent a year. If that doesn't sound much, then consider this: that's twice as fast as the rate of destruction of tropical rainforests. According to the New Scientist, in the early 1980s, around 40 percent of the region's reefs hosted live coral -- today it is just 2 percent. At risk are more than 600 species of coral (76 percent of all that is known to us) and 3,000 separate species of plants, not to mention the 120 million people who make a living from the reefs, according to AFP.

To call this situation serious, or even worrying, doesn't really give it the gravity it deserves. What the former chief scientist with the Australian Institute of Marine Science told AFP in a recent interview does: "We are precipitating a mass extinction of absolutely everything."

What is destroying the world's reefs on such a massive scale is a phenomenon known as bleaching. To the naked eye, bleaching is when the coral reefs turn white and eventually die. What is actually happening is a breakdown in the symbiotic process between the reefs and the algae that grow on them.

Corals 'bleach' when they are under stress, which typically has been caused by an increase in sea-surface temperatures (but which could be also brought on by variations in light, carbon dioxide (CO2) levels or pollutants). The stressful conditions make corals release the algae -- their source of food -- and thereby effectively starve themselves to death in the process. According to Science Daily, if the corals do not recover the algae "within a few days" of expelling them, the coral reefs eventually crumble and die.

Conversely, the algae -- and therefore the coral -- rely on CO2 for their very survival as the algae soak up the CO2 and sunlight to produce carbohydrates for the corals to eat in the first place. Its demise would be very bad news -- because CO2 levels would go up even more without the algae around to soak them up.

The algae, known as Symbiodinium, is part of a group of creatures known as dinoflagellates, which are responsible for processing one-third of all CO2 in the world's oceans, reports Science Daily. It's important to remember that around half of the 25 billion tons of air-borne CO2 emissions humans produce each year also gets absorbed by the oceans. So whatever is happening underwater matters directly to those of us on land. In short: We need to keep this algae-happy.

Scientists are already concerned about how much airborne CO2 the world's seas can take. One side-effect of too much CO2 in the water, for example, has been an increase in acidity levels. During the past 50 years oceans have become "one-third of a pH unit more acid" according to Australia's ARC Centre of Excellence for Coral Reef Studies, (CoECRS). Acidity levels affect corals and other creatures' abilities to form their skeletons, a process known as calcification. When CO2 levels increase, as does acidity levels, calcification breaks down.

We would need atmospheric CO2 levels of around 500 parts per million (ppm) to kill off the process of calcification completely, reports Mother Jones. Today, CO2 levels stand at 385 ppm. The Department of Global Ecology at the Carnegie Institution in Washington D.C. believes that, based on current emissions levels, we could reach the 500-mark by as early as 2040, according to Nature.

Bleaching episodes

The increase in bleaching episodes in recent times gives serious pause for thought. Between 1876 and 1979 -- a little more than a century -- only three coral bleaching incidents were recorded, says WWF. Between 1980 and 1993 -- slightly more than a decade -- 60 were. And in 2002 alone there were more than 400.

But the worst year to date for coral reefs was easily 1998. That year, coral bleaching occurred in 60 countries around the world, with some places hit harder than others. According to the Union of Concerned Scientists (UCS), some Indian Ocean corals suffered mortality rates of more than 70 percent.

What made 1998 so different from other years was the depth of water in which the damage occurred. Previously, says UCS, the worst impacts of coral bleaching only occurred in depths of up to 15 meters. That year, it was as deep as 50 meters.

Scientists believe that the reason 1998 was such a bad year for coral reefs was because it also happened to be the hottest year of the century, and tropical sea surface temperatures were the highest they had been in modern times.

We knew of the phenomena at the time as El Nino, and it destroyed around 15 percent of coral reefs worldwide in just six months.

The Intergovernmental Panel on Climate Change has said that if water temperatures rise by between 1 and 2 degrees over 1990 levels, virtually all coral worldwide would be affected by bleaching.

(Bleaching and acidification are not the only things corals have to worry about at the moment. A new disease, which is being called "white syndrome" has attacked coral reefs off the coast of Japan (it has also attacked parts of the Great Barrier Reef in Australia) and it has scientists more concerned about it than bleaching, reports the Asahi Shimbim. The reason: Coral reefs have been found to be able to ultimately recover from bleaching, given the proper conditions; 'white syndrome' does not appear to have a remedy.)

One of the ways to save the coral reefs is to repopulate them with fish. The problem is, in order to ensure enough fish to just meet current fishing practices would require more coral. One needs the other to survive. One square kilometer of properly managed coral reef can provide a home and breeding ground for 15 tons of fish and seafood a year, according to the World Resources Institute. But coral reefs are hopelessly overfished as it is -- more than 80 percent of the world's shallow reefs are now classified as "severely overfished" says WWF.

Just to meet existing fishing levels would require an additional 75,000 square kilometer area of tropical coral reef (that's four times the size of the Great Barrier Reef), according to a global survey conducted by the University of East Anglia in Great Britain. The amount of fish being caught on tropical reefs is apparently 64 percent higher than can be "reasonably sustained" reports the Independent.

Vital function

But ultimately it's not just fish that need coral reefs -- we do too. With the food supply issue aside (Iet's just say our dietary habits would have to change significantly if coral reefs die) reefs play a vital function in protecting our coastlines -- particularly from rising sea levels. Without them, for example, the Nature Conservancy says, "parts of Florida would be under water."

They also offer vast health benefits. Coral reefs have been used to treat cancers, HIV, cardiovascular diseases and ulcers. The coral skeletons have also been used for bone grafts, Nature Conservancy says.

The economic effects of coral reefs dying are also worth bearing in mind. According to the Nature Conservancy, 500 million of us rely on coral reefs for our food and work to the extent that it estimates reefs contribute as much as $375 billion a year in goods and services. UNEP calculates that the economic value of coral reefs works out at up to $600,000 per square kilometer.

To have any chance at all of protecting the world's reefs (aside from avoiding a temperature increase of 2 degrees Centigrade that is) scientists of CoECRS are saying that 25 percent to 35 percent of marine habitats must be made "no-go" areas permanently.

Some countries now are stepping up to the mark and enforcing bans and no-go areas around the reef systems are becoming more socially acceptable. Ireland, for example is asking the European Union to introduce a permanent no-fishing area off its coastlines where 2,500 square kilometers of deep cold water reefs grow, reports AFP. Here the reefs are affected less by warmed waters, and more by commercial fishing boats. The Philippines has also experienced some success with no-go fishing areas around its reefs.

In the meantime, scientists continue to attempt to understand how coral reefs live and die and if there is any other way of saving them. One positive discovery has been recently made by a team of Israeli researchers, who found that while acidification destroys reefs, some coral 'polyps' that live inside them can go into what appears to be a form of hibernation, only to reappear again later when conditions are normalized, AFP reports.

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One thing that may save coral reefs from the effects of global warming could be another one of the effects of global warming -- hurricanes. According to the U.S. National Oceanic and Atmospheric Administration, the cooling effect of hurricanes on sea water surfaces could help coral recover. A hurricane has the potential to cool sea temperatures by as much as 1.5 degrees Centigrade for as long as 10 days, reports the New Scientist.

However, relying on hurricanes to save the world's coral reefs is not a particularly reliable solution. In order to be effective the hurricane needs to be strong enough to cool the water -- but not so strong that it destroys the reefs. And if climate change is responsible for bringing more hurricanes, they are likely to be big ones. E-mail to a friend E-mail to a friend

(Sources: World Resources Institute; Asahi Shimbum; Mother Jones; Nature; Independent; Union of Concerned Scientists; Science Daily; Nature Conservancy; WWF; UNEP; AFP; New Scientist.)

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