Swinomish Tribe seeks to help shellfish adapt to climate change

Adding crushed shells to the beach might help offset the impacts of climate change on shellfish, according to research published recently by the Swinomish fisheries department.

Increased carbon dioxide in the environment gets absorbed by the ocean, increasing its acidity and impeding the ability of shellfish to grow shells.

“Shellfish have historically been able to pull the building blocks for their shells directly out of the sea water that surrounds them in order to form the hard structures necessary to protect them from predators,” said Swinomish marine ecologist Courtney Greiner. One of those building blocks is calcium carbonate.

Greiner designed an experiment to look at two possible ways to help growth and survival of juvenile clams affected by ocean acidification. The first is to increase the amount of algae and eelgrass, which should absorb carbon dioxide in the water column. The second is to add crushed shells to the substrate. Previous studies have shown that beach coarsening with shell hash and gravel can promote natural recruitment and growth in hardshell clams.

Surprisingly, at the test sites in Fidalgo Bay and the Skokomish delta, juvenile clam growth was greater and the water was more acidic when aquatic vegetation was absent. While the crushed shell also did not increase clam growth, its presence did reduce acidity and raise the amount of aragonite, a form of calcium carbonate, in the sediment.

“Our results do suggest that the addition of shell hash might help provide chemical refugia for clams and promote growth and survival under future ocean conditions,” Greiner said.

Under moderate carbon emission projections, pH is expected to decline by 0.2–0.3 units by 2100, making it twice as acidic as it is now. Swinomish, like other resources managers, is developing strategies to reduce the impacts of ocean acidification on culturally, economically, and ecologically important marine organisms such as shellfish.

“Harvesting shellfish is essential to the tribal way of life,” said Lorraine Loomis, fisheries manager for the Swinomish Tribe. “We need to find ways to adapt to the changing climate so that these resources will be available for future generations.”

Read the research paper here.