Global warming 'helps reefs grow'

2004-12-13 13:05

Sydney - Coral reefs around the world could grow by up to a third because of rising ocean temperatures, according to a new Australian study which turns on its head the long-held theory that global warming is killing the reefs.

Previous research predicted a decline of between 20 and 60 percent in growth of coral reefs by 2100 relative to pre-industrial levels due to increasing carbon dioxide (CO2) levels caused by the greenhouse effect in ocean surface waters.

But the newly published research, by a team led by oceanographer Ben McNeil of Sydney's University of New South Wales, suggests that present coral reef calcification rates are not in decline and are currently equivalent to late 19th century levels.

"Our analysis suggests that ocean warming will foster considerably faster future rates of coral reef growth that will eventually exceed pre-industrial rates by as much as 35% by 2100," McNeil said on Monday.

"Our finding stands in stark contrast to previous predictions that coral reef growth will suffer large, potentially catastrophic, decreases in the future."

The research was published in the latest edition of the journal Geophysical Research Letters by McNeil and colleagues Richard Matear of the government's Commonwealth Scientific and Industrial Research Organisation (CSIRO) and David Barnes of the Australian Institute of Marine Science, at Townsville in north-eastern Australia.

McNeil said their research was confined to one type of coral, which is likely to be typical of the many, but the findings would be regarded as a starting point for future research and a subject of continuing debate.

Experts say seawater surface temperatures and the quantity of carbonate in seawater dictate the growth rate of coral reefs which are built from calcium carbonate when red algae cements together a framework of coral skeletons and sediments.

The Australian scientists have observed the calcification-temperature relationship at significant reef-building colonies around the world in the Indo-Pacific and at massive Porites reef colonies in Australia, Hawaii, Thailand, the Persian Gulf and the South Pacific island of New Ireland.

They say the predicted increase in the rate of coral reef calcification is most likely due to an enhancement in coral metabolism and/or increases in photosynthetic rates of red algae.

They used projections of ocean warming and CO2 concentration from a CSIRO climate model that accounts for atmosphere-ice and ocean carbon cycles.

Matear said the results of the research shows that increases in coral reef calcification associated with ocean warming outweigh decreases associated with increased atmospheric CO2.

"While initially showing a decrease in calcification up to 1964, ocean warming outweighs the CO2 effect and stimulates recovery of coral reef calcification," he said.

"Our results represent an average over the entire coral reef community and it will be important to undertake more specific regional analysis of models to better understand future changes in regions such as Australia's Great Barrier Reef."

A two-year study released earlier this year by Queensland University scientists found the brightly-coloured corals that make up Australia's world-renowned Great Barrier Reef would be largely dead by 2050 because of rising sea temperatures.

- AFP