How to make an acid-proof oyster

Oyster farms face a fading future in acidifying oceans. But a Vancouver Island research program is trying to breed oysters that can resist the change

Gulls squawk as the normally quiet Deep Bay Marina bustles with the arrival of fishing boats assembling for an imminent commercial herring opening near Denman Island. A two-minute boat ride away from the harbour, Vancouver Island University (VIU) scientist Tim Green balances across a dock the size of a squash court decked with wet plywood slick as grease. He kneels down to haul a small black net full of juvenile Pacific oysters from the water, each one carefully numbered with a small tag. 

But the problems are even more fundamental than that: ocean acidification, sometimes considered climate change’s little-known cousin, presents a threat to the oysters’ ability to survive even past infancy.

Green is an internationally recognized expert on shellfish immunology. Several years ago, when VIU was looking for someone to head up an oyster genomics and breeding program, he jumped at the opportunity to help address an existential threat facing British Columbia’s shellfish sector worth $30 million annually in farmgate sales. Green is betting on the belief that the key to future-proofing oysters against the impacts of climate change is through breeding and selecting for oysters with traits that make them more resilient to rising ocean acidity and water temperatures.

A mollusk in the coalmine

A single axle delivery truck, loaded with fresh clams and oysters destined for Vancouver, pulls out of Fanny Bay Oysters and onto the Old Island Highway, before heading south. The midden of oyster shells piled deep outside the weathered and whitewashed Fanny Bay Oysters headquarters on the shores of Baynes Sound is a testament to longevity and more than three decades in the BC shellfish industry. 

Oysters, once settled, don’t move much. If the water gets too acidic, too warm, too nutrient-poor, or if a sudden deluge of mud smothers them, there’s not much the shellfish can do about it. The industry is much the same: unlike other fisheries, oyster growers are rooted in place. They’re accustomed to a degree of uncertainty, and when you can do little to control the growing environment, oyster mortality is an accepted cost of doing business. However, three years ago when Fanny Bay Oysters started experiencing unprecedented mortality rates, general manager Brian Yip knew something wasn’t right in the ocean.

“It’s the million-dollar question what the exact cause of increased mortality is, but it seems to be linked to water temperature and acidification,” Yip says as he looks out his office window at Baynes Sound, its busy surface like a checkerboard of oyster growing rafts.

Though many questions remain unanswered about the Pacific oyster’s ability to survive in a changing ocean environment, the link between ocean acidification and oyster health is now well understood. BC oyster growers acquire most of their seed, basically baby oysters, primarily from Chile, but also from hatcheries in the American Pacific Northwest like the Whiskey Creek Shellfish Hatchery. In the late 2000s, workers at the Whiskey Creek facility, located just south of Tillamook Bay on the Oregon coast, were faced with a sudden and big problem—hundreds of thousands of dead oyster seed. At first, low oxygen and pathogenic bacteria were considered the most likely culprits, but when these potential causes were eliminated, attention shifted to changes in the pH levels of seawater. 

A decade earlier, the scientific community had begun ringing the alarm bell about ocean acidification, but at that time there was still much to learn about the impact on marine life. 

Prompted by this wave of unexplained hatchery die-offs, Oregon State University marine ecologist George Waldbusser focused his attention on acidification. In a 2012 peer-reviewed study, Waldbusser showed definitively how acidic water impacts the ability of larval oysters to build hard calcium carbonate shells at a critical time in their life cycle—the first 48 hours. Within the span of just two days, young oysters need to build their shells and begin feeding at a rate fast enough to survive. In the presence of acidic—or corrosive—seawater, the larvae expend too much energy creating their portable homes, leaving not enough left over for these tiny mollusks to swim and feed. In the American Pacific Northwest alone, ocean acidification was costing the oyster industry an estimated US$110 million. 

Waldbusser’s scientific sleuthing also spotlighted fascinating but also troubling changes in broad earth-scale systems. Historically, pH levels in the oceans have been kept relatively stable through natural processes; the rate at which the seas were able to absorb acidifying, or pH lowering, carbon dioxide from the atmosphere was balanced by alkaline, continental erosion, and run-off. However, as anthropogenic greenhouse gas emissions soar, ocean chemistry is being thrown off balance; carbon dioxide is now increasing at a rate that scientists estimate is between 100 and 1,000 times faster than the weathering processes that produce alkalinity can keep up with. That’s why the story of the young oyster is yet another case of a canary in the coalmine of climate change.

Once scientists proved that acidity in hatchery seawater was the smoking gun, the problem had a relatively easy fix: buffering the water to raise the pH and lower acidity. But a hatchery is a closed system that enables humans to tinker with water chemistry in a way that’s not possible in the open ocean. It might take tinkering with something even more fundamental than the water they breathe.

A genetic fix

Back on Baynes Sound, Tim Green and a research assistant measure the shells of the juvenile oysters then jot assiduous notes in a logbook. Afterwards, he returns the bivalves to the net bag, sews it shut, and lowers it into the water. Air bubbles drift and pop to the surface then this bag of tiny oyster disappears into the depths of the sound. According to Green, the scientific literature is so far mixed on whether acidification negatively affects oysters after leaving the security of the hatchery. In fact, there’s some speculation that artificially buffering the hatchery seawater in which young oysters are reared may even do harm, making them less able to withstand acidification in the wild and open ocean where they will grow to maturity in just two to three years. 

“This is definitely an area that requires further research,” Green says.

And in the absence of scientific certainty, breeding a tougher, more resilient oyster, able to withstand warmer and more acidic seas, may be the only hope for shellfish cultivation that as a commercial enterprise got its start on BC’s coast in the mid 1800s, but for First Nations is a practice with a long history going back thousands of years. 

There is reason for optimism. In Green’s native Australia, the shellfish industry has a good track record breeding Pacifc oysters, which at first focused on growth rate and shell shape. In 2010, with the arrival of oyster herpesvirus in Australian waters, the industry shifted focus and was able to successfully breed oysters resistant to this virulent disease that was killing between 60 to 100% of juvenile oysters. But breeding oysters for resilience to warming and increasingly acidic oceans is new territory.  

Jim Russell, executive director of the BC Shellfish Growers Association, spends a lot of time thinking about the perilous future of the Pacific oyster, which accounts for more than 60% of BC’s shellfish sales. 

If it was simply a matter of migrating the oyster growing industry further up the BC coast where the climate is cooler and the ocean may be less susceptible to mid-summer temperature spikes, then Fanny Bay Oysters, Mac’s Oysters, Nova Harvest, and the dozens of other smaller commercial shellfish growers would pull up stakes and head north. But it’s not that easy. 

Aside from its nutrient rich waters, Baynes Sound is valuable for its proximity to a highway, an important piece of infrastructure for a product like oysters, which, when fresh, are expensive to get to market. And even if it were possible to move the industry to colder waters, that still wouldn’t mitigate the threat of ocean acidification. 

Once a grower seeds a beach with young oysters or suspends them in trays below rafts, nature looks after the rest, as long as humans look after the marine ecosystem. But the very thing that makes oysters so enviably self sustaining is also what makes them acutely vulnerable in a world where the impacts of human-caused climate change are being tallied on the balance sheets of businesses like Fanny Bay Oysters.  

“We’re environment takers, not environment makers. So yes, we believe genomics should be the focus because we can’t control these other environmental factors,” Russell says. “Sixty per cent of our industry is Pacific oysters. If we lose that, we’ll be scrambling.”

Andrew Findlay, Capital Daily, 17 March 2021. Full article.

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