The once-booming Olympia oyster, which is native to the US West Coast, could face a double threat from ocean acidification and invasive predators.
Invasive snails ate 20 percent more juvenile oysters when both oysters and snails were raised under ocean conditions forecast for the end of this century, researchers from the University of California, Davis’ Bodega Marine Laboratory found. The study highlights the dangers of multiple stressors on ecosystems, says Eric Sanford, professor of evolution and ecology and first author on the study.
“You might decide to go to work if you had a toothache. But what if you had a toothache, the flu, and a broken leg? At some point, multiple stressors will cause natural systems to break down,” he says. The work is published in the journal Proceedings of the Royal Society B.
Native Olympia oysters were once so common in San Francisco Bay that they were a cheap food during the Gold Rush, commemorated in “Hangtown Fry”—an omelet of eggs, bacon, and oysters. The population collapsed from overfishing in the late 1800s and has never recovered.
Snails and ocean chemistry
Atlantic oysters imported to the West Coast brought predatory snails such as the Atlantic oyster drill, which uses acid and a rasping tongue to drill holes in oyster shells.
Scientists have become increasingly concerned about the effects of climate change on ocean chemistry. As heat-trapping carbon dioxide builds up in the atmosphere, some of the gas dissolves in the oceans, causing a steady rise in the overall acidity of the oceans.
An interdisciplinary team of researchers at the Bodega Marine Laboratory is looking into the oceans’ future by raising animals in seawater with raised levels of dissolved carbon dioxide. In earlier work, they found that oysters raised under conditions predicted for the end of this century are smaller than present-day animals.
In Tomales Bay north of San Francisco, young snails emerge from egg capsules at about the same time of year that juvenile oysters settle from the plankton and grow into adults. Sanford and colleagues raised both oysters and snails in the lab to simulate this process under present-day conditions and with levels of carbon dioxide forecast for 2100.
They found that oysters raised under high carbon dioxide were smaller, but did not have thinner shells than oysters reared under present-day conditions. The snails were not affected by high carbon dioxide, but ate 20 percent more oysters under these conditions.
“It’s like if you go out for tacos,” Sanford says. “If the tacos are smaller, you’re going to eat more of them.”
The experiment was based on the average acidity of the oceans. However, as the overall acidity of the ocean rises, short-term fluctuations mean that locations like Tomales Bay are already experiencing peaks of acidity similar to those used in the experiment.
Apart from their culinary delights, oysters perform important ecosystem services, for example filtering material out of the water, and there have been growing efforts to restore their populations along the West Coast, including in San Francisco Bay. But the new work shows that the combination of climate change and invasive predators may make restoration increasingly difficult.
The National Science Foundation funded the research.
Source: UC Davis