Acidification of oceans threatens to change entire marine ecosystem

Ocean acidification due to excessive release of carbon dioxide into the atmosphere is threatening to produce large-scale changes to the marine ecosystem affecting all levels of the food chain, a University of B.C. marine biologist warned Friday.

Chris Harley, associate professor in the department of zoology, warned that ocean acidification also carries serious financial implications by making it more difficult for species such as oysters, clams, and sea urchins to build shells and skeletons from calcium carbonate. Acidic water is expected to result in thinner, slower-growing shells, and reduced abundance. Larvae can be especially vulnerable to acidity.

“The aquaculture industry is deeply concerned,” Harley said. “They are trying to find out, basically, how they can avoid going out of business.”

While there is potential for, say, commercial oyster growers to reduce acidity for larvae in land-based facilities, the greater marine environment doesn’t have that luxury. “For wild populations, you can’t just take part of their lifecycle and babysit it,” he said.

A total of 10,000 tonnes of oysters, clams, scallops and mussels worth $21.7 million were harvested in B.C. in 2010. The sea urchin fishery was worth another $9 million, based on a harvest of 2,300 tonnes.

Lab studies at the University of B.C. also show that acidic water can impair the ability of salmon to grow and smell properly, which has implications for their ability to find native spawning streams. Research in Australia’s coral reefs has found that acidity can erode a fish’s ability to sniff out their best habitat and to avoid predators.

Development of small creatures such as pteropods — free-swimming snails that are food for salmon — will also be stunted by acidity.

Harley was speaking in an interview at the conclusion of a week-long meeting on ocean acidification involving some 20 scientists and research students from Canada, the U.S., Scandinavia, Australia, Italy, Great Britain, and Hong Kong.

Harley said that research into ocean acidification is only about a decade old, which is why it is important to bring researchers together from different parts of the world to share findings and better understand the big picture.

“We know the impacts are going to be really widespread. The last big unknown is whether species will be able to adapt.”

Coral reefs in tropical waters also stand to be severely impacted, which he described as a pending “biodiversity catastrophe.”

On the other hand, kelp and seaweed, including those found on the B.C. coast, may benefit from increased carbon dioxide through enhanced photosynthesis. They will also benefit from a decline in grazers such as urchins and snails. “If they become less abundant or smaller, they’ll eat less kelp and that’s a win-win for the kelp.”

Purple sea stars also grow faster under acidic conditions. “That good for them, but it’s bad for the mussels, which are their favourite food,” Harley noted.

Average pH levels in the oceans have dropped form 8.2 to 8.1 and are “headed to 7.8 or below by the end of this century,” he said.

While part of the equation involves the upwelling of naturally acidic waters from the deep ocean, researchers believe that the major driver is carbon dioxide released from burning fossil fuels.

While the issue is global in scale, there are steps that can be taken locally to lessen the impact such as by reducing fertilizer runoff from farms and protecting biodiversity through measures such as marine protected areas.

“Every little bit helps. The more we can transition from fossil fuels, the better off we’ll be.”

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