Kai moana days numbered: US expert

22:55, Jun 29 2014

Better savour those oysters or green-lipped mussels while you can, because New Zealand shellfish could be obliterated by greenhouse gases.

An American expert told a University of Otago conference that a "massive shellfish extinction event" could be on the cards.

Todd Capson will speak with government officials and scientists today on what must be done to prevent the rapid disappearance of seafood lovers' favourite fare .

"It's not always a gradual change. If you exceed a certain threshold, things die."

The issue arose because CO 2 in the ocean transformed into an acid, Capson told the delegates at the Foreign Policy School seminar during the weekend.

Rising levels of the gas from carbon fuels meant more of this acid - "the same thing that makes Coca-Cola fizzy" - dissolved the substance oysters and other shellfish needed to make their shells.


Without enough calcium carbonate in the seas to make a fully developed shell in their first days of life, the baby creatures died.

Coral, which builds its reefs using the same material, is also under threat from rising levels of CO 2 in the atmosphere.

Capson said Americans have already experienced the devastation "ocean acidification" could bring.

In 2007, seafood farmers off the coast of Oregon and Washington states lost nearly 80 per cent of their shellfish stock.

Once-thriving habitats suddenly became dead zones, leaving a NZ$340 million industry that employed 2000 workers on the brink of collapse, Capson said.

Last year, affected American aquaculture workers visited their Kiwi counterparts with a chilling warning.

"This happened to me and it's going to happen to you."

During his time in New Zealand, Capson, of the US Sustainable Fisheries Partnership, will also meet with the seafood industry to discuss how ocean acidification can be monitored and farmed shellfish protected.

Globally, the ocean has become 30 per cent more acidic since the industrial revolution, he said. There were also hotspots - like the Northwest coast of the United States - which had become even more acidic.

New Zealand's aquaculture industry was yet to be affected, but tests by National Institute of Water and Atmospheric Research scientist Kim Currie showed the water's acidity was rising, Capson said.

Close monitoring of the changes in the seas was the first step.

Green-lipped mussels and other shellfish were also put at risk by run-off from the land that led to algal blooms on the coastlines, Capson said. When these blooms decomposed, they added even more CO2 to the water, making temporary acidic hotspots in which shellfish could not grow.

Radical change, including preventing run-off and reducing carbon emissions long-term, was needed to ensure such seafood species did not vanish, he said.

"If you do nothing, then that's the risk."

The Dominion Post