Ocean acidification impacts marine life on B.C. coastlines

July 26, 2016

In the 1950s, UBC marine ecologist Dr. Thomas Widdowson surveyed the distribution of algae and mussels along the south coast of Vancouver Island, B.C. Now, at three out of those 15 original sites, mussels no longer occur. Such localized extinctions are a direct result of rising temperatures, changes to ocean salinity and extreme weather events, explains Dr. Chris Harley, a marine ecologist at UBC and Peter Wall Faculty Associate, who studies ocean acidification and the impact of climate change on rocky coasts. 

“We’re pretty dependent on coastal marine systems,” says Dr. Harley. “They provide lots of food: the export value of just the shellfish harvest in Canada is more than $2 billion a year and climate change affects how well shellfish grow.”

He has many insights about the significant changes occurring on B.C. coastlines as a result of increased carbon dioxide emissions, including the impacts of ocean acidification on shellfish and sea stars.

“When carbon dioxide is absorbed into the ocean, it reacts with sea water and creates a weak acid, which is why the pH goes down. When the water is more acidic, you have more hydrogen protons floating around, and they tend to grab carbonate ions, which is one half of what you need to build clam shells or corals that are made out of calcium carbonate,” explains Dr. Harley. “This acidity reduces the availability of carbonate ions for making calcium carbonate.”

The result is that shellfish, such as mussels, have difficulty building shells. In addition, mussel beds are also affected by higher temperatures, contributing to their demise in some localized spots along the B.C. coast.

Conversely, Dr. Harley’s lab tests have shown that sea stars have fared well in warmer and more acidic waters.

“They grow faster when you warm up the water and when you add carbon dioxide to it.”

They also do better in relatively salty water, he adds. When freshwater from the Fraser River runs into the Strait of Georgia in the spring, sea stars suffer, or stay in deeper waters, away from fresh water. Mussels, in turn, can thrive as the freshwater effectively staves off their predators.

As B.C.’s climate continues to change, and less snow falls in the mountains, spring run-off into the Strait of Georgia will decrease, making water in the Strait saltier– which is good news for sea stars and therefore bad news for mussels.

All of these changes have impacts on intertidal communities. As acidic waters and higher temperatures threaten mussels but favour sea stars, mussel bed habitats are being reduced.

“You have this layer cake pattern of species on rocky shores and as you get to hotter places those species are getting pushed downwards towards the low tide line. But waiting for them are all the predators that can crawl up from below,” explains Dr. Harley, referring to sea stars.

Ocean acidification also affects aquaculture, he adds. When the ocean becomes too acidic, acquaculturalists cannot rear baby scallops since the scallops are unable to develop a hard shell. It also means that sometimes marine life moves around, perhaps to deeper waters or toward other shores, changing where seafood can be fished from.

“We are putting food security at risk, people’s careers and employment at risk and the Canadian economy at risk if we are not careful about how we deal with climate change,” he warns.

In 2006, Dr. Harley published a review paper entitled, The impacts of climate change in coastal marine systems, in which he suggests that human-induced global climate change has profound implications for marine ecosystems and the economic and social systems that depend on them.

It was a turning point in the field of marine ecology, where previously the ocean was believed to be buffered by the impacts of climate change.

“The problem is we have kept putting off making tough choices and now we have tough choices to make that may have no acceptable alternatives when it comes to preventing major ecological problems. We can’t tell people to stop burning fossil fuels. But we do need to cut back. There is a fine line between convincing people it is important and making it so depressing that people throw their hands up in the air and give up,” concludes Dr. Harley.