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  EurekAlert 15 May 06
Global warming may have damaged coral reefs forever
University of Newcastle upon Tyne

BBC 15 May 06
Warming set to 'devastate' coral
By Paul Rincon BBC News science reporter

Rising ocean temperatures look set to cause lasting devastation to coral reef systems, a study suggests.

An international team of researchers looked at reefs in the Seychelles, where an ocean warming event in 1998 killed much of the live coral. The group found the oceanic reef had experienced fish extinctions, algal growth, and only limited recovery. Details have been published in the US journal Proceedings of the National Academy of Sciences.

The 1998 event saw Indian Ocean surface temperatures rise to unprecedented levels, killing off - or "bleaching" - more than 90% of the inner Seychelles coral.

Coral bleaching has been described as a vivid demonstration of climate change in action. "[Bleaching events] are becoming more frequent and are predicted to become more severe in coming decades. They are directly linked to increases in sea surface temperatures," said lead author Nick Graham, of the University of Newcastle, UK.

'Special relationship'

Corals live in a mutually beneficial relationship with photosynthetic algae. But when sea surface temperatures at a given location rise above summer limits, the corals expel their single-celled bedfellows (possibly because the algae start producing toxins).

Algae provide corals with most of their energy and their colour - hence the term bleaching. If the high temperatures are prolonged, the corals start to die off en masse.

Bleaching in 1998 occurred in all reef regions of the world; 16% of the world's reefs were lost in that one year, alone.

But the western Indian Ocean suffered most because of an interaction between El Nino and another periodic climate phenomenon called the Indian Ocean dipole. In the seven years since, the damaged reefs have been largely unable to reseed. Many simply collapsed into rubble and became covered in algae. This collapse removed food and shelter from predators for a large and diverse amount of marine life.

The survey showed four fish species could already be locally extinct, and six species are at critically low levels. The survey also revealed that the diversity of fish species in the heavily impacted sites had plummeted by about 50%.

Computer models

Reduced biodiversity makes for a more fragile, less stable ecosystem.

The team says smaller fish have fallen in number more rapidly than larger species, but their decreased availability is having a more lasting effect on the food chain - and this effect is likely to be amplified as time goes on.

Moreover, the group's paper reports, the observed fall in herbivorous fish is a key concern, as they control algal spread.

The problems seem to be down to the relative isolation of coral systems in this area. An absence of nearby reefs to provide larvae which could settle and grow into new coral structures, along with the lack of favourable sea currents to transport the larvae, could be largely to blame.

In expansive continental reef systems such as the Great Barrier Reef in Australia, there exists more potential for so-called "refugia" which may escape the worst of the bleaching. In these areas, corals could survive and subsequently go on to repopulate the worst-hit areas.

But the prospects may not be so good if bleaching events become more common and more severe, the team says.

Since 1998, another three bleaching events have been recorded in the Indian Ocean and at least two in the Pacific. "Various [computer simulations] suggest we'll be having a 1998-scale bleaching event annually within 30 years, so the outlook is pretty bleak for how common these events will become," said Dr Graham.

Worldwide, coral reefs cover an estimated 284,300 sq km and support over 25% of all known marine species.

EurekAlert 15 May 06
Global warming may have damaged coral reefs forever
University of Newcastle upon Tyne

Global warming has had a more devastating effect on some of the world's finest coral reefs than previously assumed, suggests the first report to show the long-term impact of sea temperature rise on reef coral and fish communities.

Large sections of coral reefs and much of the marine life they support may be wiped out for good, say the international team of researchers, who surveyed 21 sites and over 50,000 square metres of coral reefs in the inner islands of the Seychelles in 1994 and 2005.

Their report is the first to show the long-term impact of the 1998 event where global warming caused Indian Ocean surface temperatures to increase to unprecedented and sustained levels, killing off (or 'bleaching') more than 90 per cent of the inner Seychelles coral.

The team, led by the University of Newcastle upon Tyne, and which comprises researchers from the UK, Australia and the Seychelles, publishes its findings today, Monday May 15, in the Proceedings of the National Academy of Sciences.

The research showed that, while the 1998 event was devastating in the short term, the main long-term impacts are down to the damaged reefs being largely unable to reseed and recover.

Many simply collapsed into rubble which became covered by unsightly algae. The collapse of the reefs removed food and shelter from predators for a large and diverse amount of marine life - in 2005 average coral cover in the area surveyed was just 7.5 per cent.

The survey showed that four fish species (a type of butterfly fish, two types of wrasses and a type of damsel fish) are possibly already locally extinct, and six species are at critically low levels (a type of file fish, three types of butterfly fish and two damsel fish), although their decline probably started to happen soon after 1998.

The survey also revealed that species diversity of the fish community had decreased by 50 per cent in the heavily impacted sites.

Reduced biodiversity results in a more fragile and less stable ecosystem.

Smaller fish have reduced in number more quickly than larger species but their decreased availability has started to have a more lasting effect on the food chain, and this effect is likely to be amplified as time goes on.

Moreover, the observed decrease in herbivorous fish is a key concern as they control algal spread.

Researchers speculate that the reefs' inability to reseed is down to their relative isolation. A lack of nearby reefs to provide larvae which could settle and grow into new coral structures and the absence of favourable sea currents to transport the larvae could be largely to blame.

Yet while a bleak picture is painted in the inner islands of the Seychelles, the survey area, from a diving perspective the outer carbonate islands still offer healthy coral reefs.

Early results from diver tourist surveys in the inner islands suggest that diver satisfaction is high with granite reefs, wrecks and whale sharks.

Lead researcher Nick Graham, of Newcastle University's School of Marine Science and Technology, said: "We have shown there has been very little recovery in the reef system of the inner Seychelles islands for seven years after the 1998 coral bleaching event."

"Reefs can sometimes recover after disturbances, but we have shown that after severe bleaching events, collapse in the physical structure of the reef results in profound impacts on other organisms in the ecosystem and greatly impedes the likelihood of recovery."

"Unfortunately it may be too late to save many of these reefs but this research shows the importance of countries tackling greenhouse gas emissions and trying to reduce global warming and its effect on some of the world's finest and most diverse wildlife."

The team comprised researchers from the University of Newcastle upon Tyne, the Australian Institute of Marine Science in Townsville; the Centre for Environment, Fisheries and Aquaculture Science, Lowestoft; the Seychelles Centre for Marine Research and the Seychelles Fishing Authority. The work was supported by grants from the British Overseas Development Administration (now DFID), the Leverhulme Trust and the Western Indian Ocean Marine Science Association.
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