NZ scientists sound warning on ocean acidification

Bluff's oyster fisheries in Foveaux Strait may be at the top of a hit list of species vulnerable to increasing acidity levels in the oceans, scientists say.

But the global phenomenon of ocean acidification may pose a threat not only to New Zealand's fisheries and aquaculture industries, but to marine ecosystems around the world, according to the national science academy, the Royal Society.

"Concerns exist over acidification and its potential, within decades, to severely affect marine organisms, food webs, biodiversity and fisheries," the society said in a paper released yesterday.

The oceans are becoming more acidic as they store more carbon dioxide from the rising levels in the Earth's atmosphere. Oceans store about 50 times more carbon dioxide than the atmosphere, and they have absorbed more than 30 percent of the carbon dioxide released by human activity.

The Royal Society is planning to hold a workshop on the issue in Wellington on September 9.

Carbon dioxide-saturated oceans pose a threat to New Zealand's corals, crustaceans and shellfish, because they may thin the calcium carbonate shells not only of the adult organisms, but their juvenile stages.

Acidification may also be threatening calcifying algae which cover 80 percent of the Otago coast and provide the habitat for larvae of species such as paua and kina. Mussels, Pacific and Bluff oysters, paua and scallops make up a $300 million industry.

A key form of calcium carbonate, aragonite, which is used by corals and other sea life may become less available before the middle of the century, according to Professor Keith Hunter, head of Otago University's chemistry department.

A National Institute of Water and Atmospheric Research (Niwa) scientist at the university, Dr Philip Boyd, said kina, mussels, oysters, and paua were among important coastal species which could be affected.

In the open ocean micro-organisms such as some plankton at the base of global food webs may be left with weaker and thinner shells.

"We will see a significant `tipping point' in terms of ocean chemistry by as early as 2030," said Dr Boyd. "We may see the shells of some of these `calcifiers' dissolve". Both scientists emphasised there were huge gaps in knowledge of how marine life and ecosystems would change, but said the only plausible way to slow down the changes was to reduce emissions of carbon dioxide.

Coastal organisms may have extra resilience because the conditions in which they live vary naturally, and corals in the southern fjords may also have some adaptions in place because of acidic tannins in bush run-off.

But Antarctic ecosystems will be very vulnerable, because colder water can take up more carbon dioxide, and many cold-water organisms such as corals are slow-growing.

Proposals for helping aquaculture adapt have included breeding species capable of tolerating acidity, reducing the acidity of water in which larval stages develop, and changing the species farmed.

Prof Hunter said Australian research had shown that Sydney rock oysters could be selectively bred to tolerate higher levels of acidity.

"There may be some future for the aquaculture industry to adapt," he said.

The September workshop has been planned to alert government and private sector agencies to the scientific and technical issues, and to inform scientists of the most important priorities in future research.