Rising ocean acidity threatens low-lying islands

Michael Perry, Reuters 2 Jun 08;

SYDNEY (Reuters) - Rising acidity in the ocean caused by seas absorbing greenhouse carbon dioxide could make low-lying island nations like Kiribati and the Maldives more vulnerable to storms as their coral reefs struggle to survive, say scientists.

Carbon dioxide in the atmosphere is at its highest level in the past 650,000 years, possible 23 million years, and half has now been dissolved into the oceans making them more acidic.

Ocean acidification, which is projected to spread extensively north from the Antarctic by 2100, makes it difficult or impossible for some animals, like coral and starfish, to produce their shells and skeletons.

"If ocean acidification weakens the structure of reef-forming corals and algae, tropical systems (islands) will be more vulnerable to physical impacts from storms and cyclones," said a new report by some of the world's leading marine scientists.

"By 2100, it is expected that some reefs will become marginal and reef calcification will decline," said the report, by the Antarctic Climate & Ecosystems Cooperative Research Centre, released on Monday.

The report cited Kiribati in the South Pacific and the Maldives in the Indian Ocean as being more vulnerable to tropical storms if ocean acidification continues to rise.

"These impacts will also directly affect important commercial, recreational or subsistence reef fisheries where the target species depend on reef habitats," said the report, released at an ocean acidification conference in Hobart.

Ocean acidification is when carbon dioxide dissolves in the sea forming a weak acid, carbonic acid. Human-induced carbon dioxide has largely been produced by burning fossil fuels, agricultural practices and concrete production.

"The ocean is a major sink for CO2 emissions and has absorbed about 48 percent of the CO2 emitted by human activities since preindustrial times," said the report.

FOOD CHAIN THREATENED

Ocean acidification is already affecting the cold water marine life of the Southern Ocean where most carbon dioxide has dissolved and U.S. researchers said it was now appearing on the Pacific North American continental shelf.

"The Southern Ocean is a biogeochemical 'harbinger' for the impacts of acidification that will spread throughout the global ocean," said the report.

By 2060, Antarctic polar waters would experience carbonate ion concentrations so low that one form of calcium carbonate, aragonite, will not be available for organisms to build shells.

Ocean acidification may also interfere with the respiration of fish, the larval development of marine organisms and the ability of oceans to absorb nutrients and toxins.

"Ocean acidification is likely to have an ecological cascade effect right up to parts of the food web that are important to human beings, such as fish and shell fish," said research scientist Will Howard from the Antarctic research centre.

The report said ice cores showed that the current rate of increase of carbon dioxide in the atmosphere is 100 times greater than the most rapid increases experienced in the last 650,000 years. Sedimentary records suggest carbon dioxide levels were higher than at anytime in the last 23 million years.

It said atmospheric carbon dioxide levels are expected to reach about double pre-industrial levels within this century, resulting in an acidification of oceans three times the level experienced during the last major rise in carbon dioxide during the last glacial period 15,000 years ago.

"Many (marine) species have taken millennia to evolve and it is unknown whether they can (or will) be able to adapt to the relatively rapid rate of ocean acidification, in the order of decades not millennia," said the report.

(Editing by Valerie Lee)