Oysters are the superstars of healthy coastal habitats. They clean pollutants from the water via filter feeding, and they build reef-like oyster beds that provide vital habitat for other sea creatures and protect shorelines from storms and erosion.

Unfortunately, these mighty mollusks are also imperiled, particularly on the U.S. Pacific Coast where a host of environmental threats over the last century have decimated native oyster beds from southern California to Alaska. Despite efforts to restore their numbers, West Coast oysters can’t seem to catch a break. A new study suggests that while warming oceans from climate change could boost their numbers, it might also unleash more predatory invasive snails called “oyster drills” that could further diminish native oyster populations — or finish them off for good.

Oysters galore

A cluster of Olympia oysters Olympia oysters, which were a key staple for Native Americans and Gold Rush forty-niners, are now nearly extinct. (Photo: Oregon State University/flickr)

U.S. Pacific coastal estuaries once brimmed with Olympia oysters, the only native species in the region (scientifically known as Ostrea lurida). These tiny — and tasty — shelled sea creatures figure prominently in local lore, first as a key staple for Native Americans and later as a favorite coppery-tasting delicacy among the fortune-seekers of California’s Gold Rush.

Unfortunately, their popularity has contributed to their downfall. Overfishing, along with sedimentation, pollution and disease, have decimated native oyster populations along all U.S. coasts by 88 percent over the last century, according to a 2012 study published in the scientific journal Proceedings of the Royal Society B. Perhaps hardest hit is the West Coast where researchers found that Olympia oysters were functionally extinct in every estuary studied.

For oyster lovers in California, Oregon and Washington, that means settling for farm-raised Pacific oysters native to Asia.

Not that efforts aren’t underway to bring back the region’s beloved indigenous bivalves. The Nature Conservancy and the National Oceanic and Atmospheric Administration, as well as other groups, have worked on dozens of restoration projects up and down the Pacific coast over the last two decades. Interestingly, the aquaculture industry, which has increasingly felt the impact of shell-dissolving ocean acidification on its Pacific oyster yields, is also working to bring back native Olympia oysters due to their greater resilience to acidification.

Predatory practices

native oyster survived drilling attempts This native oyster has survived four drilling attempts by invasive predatory snails. (Photo: Brian Cheng/UC Davis)

So far restoration efforts have brought small successes that environmentalists hope will multiply. But climate change is casting doubt on how far things can go.

A new study by University of California-Davis researchers, published in the journal Functional Ecology, found that while warming oceans are good in the long term for Olympia oysters, which tend to grow faster in balmier waters assuming they have enough food, it’s also good for one of their fiercest enemies: oyster drills. These voracious snails bore through oyster shells and rip out pieces of the soft bodies inside, and they become more ravenous as water temperatures rise.

“To me, it’s the worst way to go,” says lead author Brian Cheng, quoted in this University of California, Davis news article. “Imagine you’re an oyster. You have a suit of armor you wear and that you cannot move. Imagine there was something that could crawl onto you and begin blasting away on your shell of armor. Imagine they could secrete acid and use a file-like tongue to bore tiny little holes into the shell. Then they insert their tongue and tear away bits of flesh, eating you alive. Once the hole is made, the oyster is basically done.”

Watch oyster drills in action here:

Cheng, who was a doctoral candidate at UC Davis Bodega Marine Laboratory at the time of the study and is currently a postdoctoral fellow at the Smithsonian Environmental Research Center, found that oyster drills thrive best in water a few degrees warmer than normal — pretty much the amount of warming forecast over the next few decades.

So, while Olympia oysters also do well in warmer waters and survive extreme temperature spikes better than their snail predators, oyster drills may well reign under these ideal conditions in the short term. In fact, Cheng and his team determined these invasive snails, introduced to the Pacific from the East Coast and Asia, could outpace native oysters over the next 30 years, possibly wiping them out in a feeding frenzy before they have their chance to get the upper hand.

“We know that [oyster drills] have already begun to do so,” says Cheng in a Capital Public Radio podcast (listen here). “We have data from Tomales Bay (California) which shows that oyster drills have eliminated much of the oysters in parts of that estuary. So we know that it’s ongoing, and this work suggests that it could be worse.”

Farmed oysters were not part of the research, but predatory snails are also a threat to them.

On the bright side, Cheng says oyster drills are relatively easy to pick out of the water by hand and eradicate. This could give Olympia oysters (and their farmed cousins) an additional leg up on survival.

Still, the resurgence of native oyster populations with warmer waters is by no means a “slam dunk.” As Cheng notes: “Other aspects of climate change, such as ocean acidification, may continue to be detrimental to oysters.”