Global warming may have damaged coral reefs forever

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.

Source: University of Newcastle upon Tyne

Related stories:

Marine invasive species advance 50km per decade
A rapid, climate change-induced northern migration of invasive marine is one of many research results announced Tues. Nov. 11 during opening day presentations at the First World Conference on Marine Biodiversity, Ciudad de las Artes y las Ciencias, in Valencia.
Study: Wildlife need more complex travel plans
A new UC Davis study says that people trying to help nature by designing corridors for wildlife need to think more naturally.
Diversity of plant-eating fishes may be key to recovery of coral reefs
For endangered coral reefs, not all plant-eating fish are created equal. A report scheduled to be published this week in the early edition of the journal Proceedings of the National Academy of Sciences suggests that maintaining the proper balance of herbivorous fishes may be critical to restoring coral reefs, which are declining dramatically worldwide. The conclusion results from a long-term study that found significant recovery in sections of coral reefs on which fish of two complementary species were caged.
Turf wars: Sand and corals don't mix
When reef fish get a mouthful of sand, coral reefs can drown. That's the latest startling evidence to emerge from research into the likely fate of reefs under climate change and rising sea levels, at the ARC Centre of Excellence for Coral Reef Studies (CoECRS).
Low voltage current to stimulate growth of coral off South Florida coast
The thunderclaps and lightning flashes of Victor Frankenstein's laboratory seem far removed from the sunshine, hotels and snorkelers of the South Florida coast. But the town of Lauderdale-by-the-Sea is pursuing the dream of using electricity to help generate life.
Fishy future written in the genes
The roadmap to the future of the gorgeously-decorated fish which throng Australia's coral reefs and help earn the nation $5 billion a year from tourism may well be written in their genes.
Explorers find hundreds of undescribed corals, other species on familiar Australian reefs
Hundreds of new kinds of animal species surprised international researchers systematically exploring waters off two islands on the Great Barrier Reef and a reef off northwestern Australia -- waters long familiar to divers.
World's water ecosystems under threat
(PhysOrg.com) -- Human activities such as fishing and water use are over-riding the effects of global warming on the ecosystems that support the world’s water and fish supplies, experts have revealed.

News discussion:

Irresponsible GW science in Space & Earth science news