by Alejandro Moses de la Vega

For many species, rising global temperatures will strain their ability to survive. However, a hotter climate might not be the end for one threatened species of oyster, according to a recent study.

The Olympia oyster is the only species of oyster native to the West Coast of North America. It was a staple in Native American diets in precolonial America, and became a major economic resource during industrialization. But its numbers took a hit in the early 20th century, thanks to pollution and overfishing.

“Few people have ever seen or eaten one,” said Kerstin Wasson, lead author of the paper and research coordinator of the Elkhorn Slough National Estuarine Research Reserve.

The introduction of the competitive Pacific oyster and the predatory Atlantic snail exacerbated the problem. However, scientists aren’t entirely sure by how much—a lack of historical data on past oyster populations poses a problem.

“It’s really challenging to go back 100 years or 200 years or more and say, all right, here’s what it looked like,” said Andy Chang, a co-author and marine biologist at the Smithsonian Environmental Research Center’s branch in San Francisco (SERC-West).

Only 7% of Olympia oyster populations in the study fit the definition of “ecologically significant” oyster beds—populations with more than 10,000 oysters. On top of their function as natural filtration systems, oyster beds are also habitats for many fish and invertebrates. Restoring them could create life-sustaining ripples throughout the entire ecosystem.

Which begs the question: Can Olympia oyster restorations survive climate change?

To predict how these embattled bivalves will deal with climate change, a coastwide network known as the Native Olympia Oyster Collaborative pooled its resources along the Pacific Coast. The team looked at 26 sites in total, from British Columbia in the north to Baja California in the south. The hottest sites near the equator acted like “crystal balls” forecasting the future of oysters further north.

 At each site, the scientists identified the shallowest depths where oysters appeared. They also looked for evidence of oyster die offs. These could indicate death by heat wave and give insight into what temperatures would be lethal for future oysters. 

Many Olympia oysters live in the intertidal zone, where the ocean retreats with the tides. This means oysters can spend substantial amounts of time out of the water during low tide, when they’re exposed to potentially scorching air temperatures. The scientists anticipated that hotter temperatures closer to the equator would be more hostile to the oysters. As a result, oysters in the south should have preferred deeper waters, where they would be exposed to the air less often.

“You can imagine how hot a sea star might get sitting out in the midday sun at low tide, which is why you typically find sea stars low down on the shore in pools,” Wasson said. “So we expected that Olympia oysters in the hotter southern end of their range, in SoCal and Mexico, would be limited to lower elevations.”

But instead, the scientists found that Olympia oysters near the equator moved even further up shore into the shallows, as though embracing the heat. Colder air, not hotter, seemed to be what stopped their expansion.

“Oysters, unlike many other species, are likely to do just fine with some amount of increased air temperature,” said Chela Zabin, another co-author and researcher at SERC-West. “If there are fewer days of freezing air temperatures in the northern part of the range, oysters may be able to exist higher in the intertidal zone.”

The research team sees this study as a perfect example of where restoration funding makes sense. It also highlights the importance of double checking our assumptions. The scientists went into the study expecting to find that Olympia oysters would suffer from higher temperatures, and found the exact opposite.

More importantly, Wasson said, it proves that restoration projects for Olympia oysters are worthwhile. Without this study, an important and unexpected dimension of Olympia oyster’s reaction to global warming could have gone unnoticed.

“This species provides a rare bright spot, a vital coastal species that is resilient to climate change,” Wasson said. “Restoration of Olympia oysters is a sound investment for the future.”

In other words: Don’t count out the West Coast’s only native oysters just yet.

The full study, “Setting the limit: cold rather than hot temperatures limit intertidal distribution of a coastal foundation species,” is available in the journal Marine Environmental Research at https://www.sciencedirect.com/science/article/pii/S0141113625002065

More Olympia Oyster Stories:

A Diverse Portfolio Is Good for Oysters Too

“Portfolio Approach” Can Help Protect Restorations From Extreme Climate