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Thursday, May 26, 2011

Study shows that ocean acidification poses threat to endangered northern abalone

Bad news for an icon of the B.C. coast: a new study shows that ocean acidification is a risk to the prized and endangered northern abalone.

In this study, researchers from the University of British Columbia and Simon Fraser University subjected larval abalone to seawater with varying levels of dissolved carbon dioxide and then watched, waited, and weighed. The results were not encouraging, as the larvae subjected to increased carbon dioxide displayed reduced shell growth (or, in the case of the highest dose group, sometimes didn't even grow shells at all), increased incidence of shell abnormalities, and decreased survival.

This is particularly bad news because B.C.'s northern abalone aren't just any shellfish. Long prized by First Nations for their meat and their shells, northern abalone were markedly reduced by commercial over-exploitation during the late 1970s and 1980s. A moratorium on commercial fishing for abalone was put in place in 1990, but stocks have continued to decline, with poaching and poor reproductive success posing two of the biggest challenges to recovery. Today, they are listed as Endangered by COSEWIC and Threatened under the Species At Risk Act, and all fishing for abalone is banned. Still, the species is simply struggling to recover, and the revelation that acidified ocean water can substantially impede larval development is sobering.

But it's not surprising. Ocean acidification is widely understood to be a primary threat to many shell-building marine species.

The basis of ocean acidification is pretty straightforward: humans have increased atmospheric concentrations of carbon dioxide over the past few decades, and oceans have absorbed a lot of it - roughly 1/3 of it, in fact. While this has helped slow the advent of climate change, the problem is that carbon dioxide combines with seawater to form carbonic acid.

For those without superhero vision, that bottom line says
"carbon dioxide plus water equals carbonic acid"
This acid in turn reduces the availability of carbonate ions - which are critical building blocks for countless shell-building animals in the ocean. The concern is that as ocean waters become 'more acidified', many shell-building organisms will struggle to build and maintain their shells. Instead of living in water that has plenty of carbonate ions to go around, these shell-building organisms may increasingly be finding themselves in water that is itself grabbing at carbonate ions.

To paraphrase a well-known analogy (and I don't know who came up with this first, but it certainly wasn't me), imagine you were building a house out of bricks and all of a sudden a bunch of thieves moved in and started stealing your bricks. As the amount of thievery increased, the amount of time and energy you'd have to use just obtaining and keeping your bricks would also increase, and your house would suffer as a result - it might be smaller, use fewer bricks, or worst of all, not even get built. This is essentially the problem that many animals will face when they try to build shells with carbonate in acidified waters - and from this latest study, it seems that the northern abalone is one more species that does not handle those extra carbonate thieves well.

Unfortunately for northern abalone, if you are an animal that is susceptible to acidification, the Pacific coast of North America not a good place to be. Our carbon dioxide emissions have increased the area affected by this coast's naturally-occurring seasonal upwellings of low pH ("acidified") waters. We are already seeing the impacts of acidification on commercial shellfish operations, as oyster growers along the U.S. west coast have struggled for the past several years with crashes in larval survival.

It's examples like these that are increasingly unifying fishermen, scientists, and environmentalists on the need for immediate action to fight ocean acidification. While the only real solution - reducing our carbon dioxide emissions - remains daunting, we now have one more reason to act - to save the endangered northern abalone.

Visit our website to learn more about ocean acidification and to send a message to our political leaders urging them to take action on this issue.

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