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Canaries in a coal mine: What shellfish can teach us about ocean acidification

U.S. West Coast oyster producers have been experiencing a dire shortage of oyster seed over the past four years which appears to be linked to changing ocean conditions, and particularly the effects of ocean acidification. Olympia OysterOyster reproduction in the wild has been almost non-existent, and mortality rates of hatchery-produced larvae in two of the four West Coast hatcheries have been as high as 80 percent compared to normal production rates. Combined, the lack of adequate oyster seed is already resulting in lower harvest rates, and some companies are considering the possibility of going out of business altogether.

Although the ocean conditions leading to larval mortalities are not thoroughly understood, a correlation has been detected between larval mortalities and upwelling events that bring highly acidic, low oxygen waters up from the continental shelf and onto the nearshore. For the past two years, Whiskey Creek Hatchery in Oregon has been monitoring upwelling events and regularly measuring pH (acidity) and Vibrio tubiashii, a naturally-occurring marine bacteria. Low pH levels and high concentrations of the Vibrio bacteria have both proven deadly to young seed oysters. Within hours after upwelling occurs, Whiskey Creek Hatchery reports a dramatic lowering of the pH level in water pumped into the hatchery from Netarts Bay, as well as high Vibrio tubiashii populations. Larval mortalities always follow.

The correlation between ocean conditions and upwelling events has not been established at the Taylor Hatchery which is located in Hood Canal, farther away from incoming oceanic waters. Although they have measured high concentrations of Vibrio tubiashii and low levels during oyster seed mortality events at the hatchery, correlations with upwelling events from the ocean have not been correlated to-date.

Environmentally, reduced populations of bivalves, a critical keystone species in the marine ecosystem, would have significant consequences. The reduction in water filtering performed by shellfish will negatively impact water quality, and diminished shellfish assemblages will reduce forage and refuge opportunities for the host of marine flora and fauna that utilize shellfish beds. Like the proverbial “canary in a coal mine” the seed shortage crises has consequences that carry up the food chain. Therefore our ability to more fully understand the dynamics at play will provide benefits that go well beyond shellfish farmers and their local communities.


The oyster shortage has dire economic repercussions as well. The ‘farm-gate’ value of oysters, clams, geoduck and mussels on the West Coast of the U.S. was $111 million as of 2007, with oysters accounting for 76% of all shellfish produced. West Coast farms provide over 3,000 family-wage jobs in rural coastal communities, and when related service sectors and suppliers are included, the total economic contribution of the shellfish farming community on the West Coast is estimated at $278 million annually. Conservative estimates of diminished production levels at the current rate of seed production cut this total economic contribution by approximately $83 million, with the specter of a continued steep decline in losses if we fail to act and current trends hold.

As a result of this crisis, a team of growers, hatchery experts, researchers and agency personnel have developed the “Emergency Oyster Seed Project,” which consists of four priority actions designed to prop up the shellfish growers in the short term, while implementing long-term monitoring programs that will help guide the way to solutions in the long term.

So far, funding for portions of the emergency project have been cobbled together through the Washington Department of Fish and Wildlife, and the Puget Sound Partnership (with a grant from the EPA) that have allowed researchers to begin monitoring programs in key Washington estuaries. The data that will be collected will help scientists better understand ocean conditions that affect shellfish mortality. Salinity, temperature, oxygen, pH and other parameters will be measured and compared to naturally occurring Olympia and Pacific oyster larval sets. Field experiments in Willapa are also being conducted to identify disease resistant oyster families. Additional research to develop an assay test to easily detect Vibrio tubiashii is expected to receive funding through USDA in the coming months.

The ability to retrofit hatcheries is seen as one of the most critical solutions, particularly if wild oyster sets continue to be poor. Small-scale experiments have proven that water quality treatments can be implemented within closed hatchery systems that optimize oyster seed survival. The funding for this component of the emergency plan has not been raised to-date, although Washington State Senator Maria Cantwell has put forth a budget request of $600,000 for FY 2010 that would provide needed funds.

As we become more aware of the affects – or potential affects - of ocean acidification on our marine environment and the ramification these affects may have on a global scale, it may be that the lessons we learn from these initial shellfish experiments will help us appreciate the seriousness of the problem and the potential for solutions.


PCSGA logoContributed by Robin Downey of Pacific Coast Shellfish Growers Association (www.pcsga.org). Founded in 1930, the Pacific Coast Shellfish Growers Association (PCSGA) represents growers in Alaska, Washington, Oregon, California, and Hawaii. Members grow a wide variety of healthy, sustainable shellfish including oysters, clams, mussels, scallops and geoduck. PCSGA works on behalf of its members on a broad spectrum of issues, including environmental protection, shellfish safety, regulations, technology, and marketing.

Posted August 3, 2009

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