They are the rainforests of the sea, providing food and shelter for millions of marine creatures.
Richard Alleyne, The Telegraph 1 Jan 09;
But now tropical coral reefs are facing a renewed - and hidden - threat from environmental change which is stunting their growth, claim scientists.
Researchers looking at the world's biggest and best preserved reef - the Great Barrier Reef - found that it is growing at its slowest rate for at least 400 years.
While the damage is not visible to the naked eye scientists believe it is a "very worrying" indicator which could spell disaster for the biodiversity of the seas.
Corals, which absorb calcium from the sea to make their hard stone like structure, grow in yearly cycles and using x-rays scientists can measure the annual growth rings.
They have discovered that while growth between 1900 and 1970 increased, it has subsequently started to decline at a rapid rate.
Professor Glenn De'ath, who carried out the research at the Australian Institute of Marine Science, believes that the increased acidification of the sea due to the absorption of carbon dioxide from the atmosphere is the main culprit.
With CO2 levels expected to double in the next 50 years, he believes the changes in the biodiversity are "imminent"
The team, which published the findings in the journal Science, looked at a total of 328 colonies spanning the 1,600 mile long reef which is off the north east coast of Australia.
They found that calcification rates increased 5.4 per cent between 1900 and 1970, but have dropped 14.2 per cent from 1990 to 2005, mainly due to a slowdown in growth from 1.43 centimetres per year to 1.24 centimetres per year.
Clive Wilkinson, global coordinator of the Global Coral Reef Monitoring Network, said decline is "here and now and over the past decade, not some time in the future, as we predicted."
"This has been happening under our noses," he added.
Ocean Acidification Hits Great Barrier Reef
Coral growth has been sluggish since 1990 due to an increase in both sea temperature and acidity as a result of global warming
David Biello, Scientific American 1 Jan 09;
The largest coral reef system in the world—and the biggest sign of life on Earth, visible from space—is not growing like it used to. A sampling of 328 massive Porites coral (large structures resembling brains that are formed by tiny polyps) from across the 133,000-square-mile (344,000-square-kilometer) reef reveals that growth of these colonies has slowed by roughly 13 percent since 1990.
The most likely reason is climate change caused by increasing carbon dioxide (CO2) and other greenhouse gases in the atmosphere, according to a new paper published today in Science.
The burning of fossil fuels over the past century or so has driven atmospheric CO2 levels from 280 parts per million (ppm) to 387 ppm—and growing. More than 25 percent of this extra CO2 is absorbed by the world's oceans and reacts with seawater to form carbonic acid. A rising carbonic acid level means a more acidic ocean.
And a more acidic ocean is bad news for coral and other sea creatures, which form their shells from calcium carbonate they extract from seawater. The more acidic the water, the more difficult it is to build the shells in the first place—as well as keeping them from dissolving.
To probe how corals are faring, marine biologist Glenn De'ath and colleagues at the Australian Institute of Marine Science in Townsville, Queensland, examined Porites coral samples stretching as far back as 1572. Because Porites lay down annual layers—like tree rings—changing environmental conditions are etched into their skeletons.
The record has not been good in recent years: Since 1990 coral have been extending and thickening by less and less each year. "The data suggest that such a severe and sudden decline in calcification is unprecedented in at least the past 400 years," the researchers wrote.
"This study put all this worry and discussion [about ocean acidification] into a real-world context," says marine biologist John Bruno of the University of North Carolina at Chapel Hill. "It shows that coral growth is indeed slowing—over a huge range and at many reefs—potentially due to increased acidity."
Slower growth will mean both that existing coral will find it difficult to cope with escalating acidity and rising sea levels. This will have enormous knock-on effects in sea life that relies on coral reefs for habitat—as well as human fisheries and other ecosystem services.
In the meantime, it appears that changes in sea temperatures and increased acidity are already beginning to impact the Great Barrier Reef. "Our data show that growth and calcification of massive Porites in the Great Barrier Reef are already declining and are doing so at a rate unprecedented in coral records reaching back 400 years," the researchers wrote. "These organisms are central to the formation and function of ecosystems and food webs, and precipitous changes in the biodiversity and productivity of the world's oceans may be imminent."
Coral growth slows sharply on Great Barrier Reef
Reuters 1 Jan 09;
LONDON, Jan 1 (Reuters) - Coral growth since 1990 in Australia's Great Barrier Reef has fallen to its lowest rate for 400 years, in a troubling sign for the world's oceans, researchers said on Thursday.
This could threaten a variety of marine ecosystems that rely on the reef and signal similar problems for other similar organisms worldwide, Glen De'ath and colleagues at the Australian Institute of Marine Science said.
The Great Barrier Reef is the world's largest coral expanse, and like similar reefs worldwide is threatened by climate change and pollution.
"These organisms are central to the formation and function of ecosystems and food webs, and precipitous changes in the biodiversity and productivity of the world's oceans may be imminent," the researchers wrote in the journal Science.
Coral reefs, delicate undersea structures resembling rocky gardens made by tiny animals called coral polyps, are important nurseries and shelters for fish and other sea life.
They also protect coastlines, provide a critical source of food for millions of people, attract tourists and are potential storehouses of medicines for cancer and other diseases.
De'ath and his team studied 328 large coral colonies from 69 reefs and found the skeletal records indicate that calcification -- or the deposit of calcium carbonate -- by these creatures has declined by 13.3 percent throughout the Barrier Reef since 1990.
The researchers blamed a combination of global warming, ocean acidity level and decreasing carbonate content in seawater for the decline, unprecedented over the past 400 years.
"Verification of the causes of this decline should be made a high priority," the researchers said.
Coral covers about 400,000 square km (154,000 sq miles) of tropical ocean floor, but needs sustained sunlight, warmer waters and high levels of carbonate to flourish.
The biggest is Australia's Great Barrier Reef, a collection of 2,900 reefs along 2,100 km (1,300 miles) of Australia's northeast coast in a marine park the size of Germany. (Reporting by Michael Kahn; editing by Maggie Fox and Mark Trevelyan)
Coral growth declines sharply on Great Barrier Reef
ABC News 2 Jan 09;
New research on the Great Barrier Reef says coral growth has fallen to the slowest rate in more than 400 years.
The Australian Institute of Marine Science's Glenn De'ath says banding like tree rings on the giant Porites coral reveals a massive decline in the growth history.
"Around about 1990 things have changed and coral calcification - that's a measure of how corals grow - has decreased by about 14 per cent since then," he said.
In the journal Science the research team says ocean absorption of atmospheric carbon may be as much of a problem as rising temperatures.
"The increased acidity levels in the ocean, we believe, is affecting things that calcify, things like corals," Dr De'ath said.
He says the decline in growth is unprecedented.
"It was relatively consistent over those 400 years or so, there would be small undulations, where as now we are experiencing growth which is consistently declining," he said.
Dr De'ath says a rough estimate suggests that coral growth could hit zero by 2050.
Great Barrier Reef decline blamed on global warming
Graham Readfearn, news.com 2 Jan 09;
CORALS on the Great Barrier Reef are growing slower than at any time in at least 400 years and leading scientists are blaming climate change.
As a major study is being published in the US, scientists fear the reef is showing signs of mass coral bleaching, last seen in 2002.
Glenn De'ath, co-author of the research published in Science magazine, said the corals would stop growing altogether by 2050 if the trend identified in the study continued.
"When you disturb an ecosystem in this way, you get a cascading effect. You then get a chain reaction -- the fish habitat is lost," Dr De'ath said.
Researchers examined more than 300 coral samples, some more than 400 years old, taken from Reef sites.
While the study looked only at Great Barrier Reef samples, the findings have implications for reefs around the world.
The study concluded corals grew steadily until 1990, when samples revealed a "severe and sudden decline" in growth.
Dr De'ath, of the Australian Institute of Marine Science in Townsville, said corals were likely reacting to the increased acidity of the ocean due to higher levels of carbon dioxide in the atmosphere. This acidification made it harder for corals to form skeletons, he said.
Warnings of a high risk of coral bleaching on the northern parts of the Reef from December to February were issued by the National Oceanic and Atmospheric Administration in the US and the Great Barrier Reef Marine Park Authority.
Bleaching occurs when coral discards the coloured algae which it relies on for nutrients.
University of Queensland coral scientist Ove Hoegh-Guldberg said weather conditions mirrored those seen before the 1998 and 2002 mass bleaching events.
"These previous events involved over 50 per cent of the reef bleaching and about 5 to 10 per cent of affected corals dying. It's difficult not to come to the conclusion we are headed for a similar scale incident," he said.
"We are starting to see the beginnings of coral bleaching on the reef flats surrounding Heron Island (on the southern end of the reef). I don't think it looks very good at all."
Of the Science research, he said: "We may have seriously underestimated the rate of climate change and this should compel us to drastic steps to decarbonise Australian and global economic systems."
AIMS chief executive Ian Poiner said a research vessel which returned from northern reef sites on December 23 had found only a small number of reefs showing signs of bleaching.
But he said scientists were on stand-by to visit any bleached areas to gather information on the types of corals most affected.
Declining Coral Calcification on the Great Barrier Reef
Glenn De'ath, Janice M. Lough, Katharina E. Fabricius
Science website 2 Jan 09;
Reef-building corals are under increasing physiological stress from a changing climate and ocean absorption of increasing atmospheric carbon dioxide. We investigated 328 colonies of massive Porites corals from 69 reefs of the Great Barrier Reef (GBR) in Australia. Their skeletal records show that throughout the GBR, calcification has declined by 14.2% since 1990, predominantly because extension (linear growth) has declined by 13.3%. The data suggest that such a severe and sudden decline in calcification is unprecedented in at least the past 400 years. Calcification increases linearly with increasing large-scale sea surface temperature but responds nonlinearly to annual temperature anomalies. The causes of the decline remain unknown; however, this study suggests that increasing temperature stress and a declining saturation state of seawater aragonite may be diminishing the ability of GBR corals to deposit calcium carbonate.
Australian Institute of Marine Science, Townsville, Queensland 4810, Australia.
Read more!
Posts
visitors since Nov 07