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Hope on the Half-Shell

Native Olympia oysters more resilient against ocean acidification

 

The Olympia oyster (Ostreola conchaphila), the native oyster of the Pacific coast of the US that was at one time deemed "functionally extinct", could hold the key to the future of the region's shellfish industry. Photo by Cheryl Lowe, courtesy of the Jefferson County (Washington) Marine Resources Committee.

With ocean acidification taking its toll on oyster production in the Pacific Northwest, several major Oregon and Washington producers have set up operations in Hawaii, which for the past few years has served as a major nursery for oysters sent to the US mainland. But Oregon State University (OSU) researchers say that Olympia oysters – Oregon's only native species of oyster that was at one time deemed "functionally extinct" – could hold the key to the future of the region's shellfish industry.

In 2005, wild and hatchery oysters along the Washington and Oregon coasts – among them Whisky Creek Shellfish Hatchery in Netarts Bay, Oregon, Taylor Shellfish Farms on Dabob Bay in Quilcene, Washington, and several hatcheries on Willapa Bay, Washington – began to die off by the millions in their larval stages. Between 2006 and 2008, mortality rates rose as high as 80 percent, shoving the commercial oyster seed industry and the lucrative Pacific Northwest shellfish business to the brink of collapse.

Initial concerns focused on viral or bacterial infection, prompting hatchery managers to instigate extensive, expensive, primarily ineffective anti-bacterial measures to filter out pathogens and disinfect incoming water.

Eventually, researchers from OSU and the National Oceanic and Atmospheric Administration (NOAA) pointed at changes in ocean chemistry – ocean acidification triggered by the cumulative effects of climate change – as the potential culprit. In 2012, OSU researchers George Waldbusser, Burke Hales, Brian Haley and Chris Langdon found a clear connection between acidification and oyster seed production woes. Elevated carbon dioxide levels in seawater, they noted, inhibit larval oysters from developing their shells and growing at a pace to make commercial production cost-effective.

Documenting the connections between shell formation rate and sensitivity to acidification provided a vital key to resolving the infant mortality undermining the shellfish industry. Now Waldbusser and fellow researchers have discovered something else that could, at least, offer a niche market for shellfish producers.

Olympia oysters, native to Pacific Northwest waters along the coasts of Canada (British Columbia), Washington and Oregon, have certain reproductive differences that make them more resilient in a changing ocean compared to non-native Pacific oysters.

Waldbusser said Olympias take more time to develop their shell – days instead of hours – saving much-needed energy to fend off the effects of an acidic ocean. He calls it "a unique trait that allows native oysters to survive surprisingly high levels of acidification." Pacific oysters have just six hours after fertilization to develop their shells. When exposed to acidic water during this critical stage, the fledgling oysters can rapidly deplete their energy reserves, making it less likely for them to survive. Olympias don't start developing their shells until two to three days after fertilization and do so at a much slower overall rate.

Spawning methods also play a role.

"Pacific oysters churn out tens of millions of eggs, and those eggs are much smaller than those of native oysters, even though they eventually become much larger as adults," Waldbusser noted.

Building an oyster shell saps energy from the fledgling oysters, but because Olympias produce fewer, larger eggs, each one uses less relative energy, compared to Pacifics, during the early stages of development.

Researchers also note that many bivalve species "broadcast spawn" – the eggs and spawn are released into the water. Olympia oysters are fertilized internally before being released into the environment, giving them a little added protection from harsh ocean conditions. Olympias can thus spend more time developing shells and dealing with acidified water.

The researchers say cultivating the native oysters could provide at least a small hedge against potentially catastrophic Pacific oyster losses caused by rising levels of ocean acidification.

Another possibility is "to breed for specific genetic traits," says Chris Langdon, who directed the molluscan broodstock program for many years at OSU's Hatfield Marine Science Center in Newport, Oregon. Breeding beneficial Olympia traits into Pacific oysters could get them to produce fewer, bigger eggs or slow their rate of shell development, enhancing their survival chances.

A key observation for Waldbusser is that Olympias didn't develop their traits as a response to rising acidification.

"Here's a trait they already possess," he said, speculating on the possibilities of "finding traits in other organisms" that could prove beneficial. "It gives us hope that there are ways organisms can persist in our changing ocean environment."

Langdon is leading efforts to use selective breeding techniques to isolate such favorable traits that could protect oysters from the ocean's rising acidity and other threats. Even so, researchers say stressors from an ever-changing ocean environment could make oysters and other marine life more vulnerable than ever. Olympia oysters can be sensitive to acidification in later stages of their lives, researchers note, but their early beneficial traits give them a much better chance of survival.

Oysters are a prime example of what can happen when outside factors impinge on natural processes and habitats.

Olympia oysters once thrived along the Pacific coast from Baja, California to Vancouver Island off the coast of British Columbia, Canada, but overharvesting and habitat loss severely depleted their numbers, researchers note. Fishery managers say that Olympia oysters were at one time so plentiful in Yaquina Bay on Oregon's central coast that their harvest contributed to the establishment of Newport and a small upriver town known as Oysterville. While Newport still thrives as a commercial fishing port with an active fleet and busy waterfront, Oysterville is long gone, the only sign of its former existence a roadside historical marker.

The native oysters nearly succumbed, too, but still sparsely inhabit Oregon's Yaquina, Netarts and Coos bays. Workers at Oregon Oyster Farms near Newport often find little Olympias attached to their farmed Pacific oysters' shells. While a few commercial growers cultivate Olympias (or Olys as they are known among culinary aficionados), mostly in Washington's Puget Sound or British Columbia, their significantly slower growth rate and smaller market size – about the size of a 50-cent piece – make them a riskier business investment.

Their diminutive growth and size will likely prevent Olys from becoming a big part of the commercial oyster market, but many analysts and shellfish managers say the small mollusks could end up filling a potentially lucrative market niche for those who crave their distinctive flavor.

Which gives them all hope on the half-shell.

 
 

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