OCEAN: RESEARCH ARTICLE Download "OCEAN 31"

Acidification and Oyster Mortality

Image courtesy of Martha's Vineyard Shellfish Group

Rising pH Levels Linked to Increased Spat Mortality. Economic, Ecological and Social Impacts on West Coast Oyster Industry

Ocean acidification is a present and future threat to a variety of ecosystems and biological processes (detailed in the OCEAN 30 issue by Safe Harbor), and one of the more recent and publicized victims of global warming is the oyster industry of the United States’ West Coast.

The oceans act like carbon sinks, and anthropogenic fossil fuel emissions have caused seawater to be 30% more acidic than pre-industrial times on a logarithmic scale. The eastern Pacific of the United States is particularly vulnerable to this decrease in pH because it already experiences deep upwelling and therefore inherently encounters more extreme acidic conditions more often. The driving force for the oyster farm failures along this shoreline is the inability for young oysters (known as spat) to develop successfully. The oysters are most vulnerable when young and just forming their calcium carbonate shells. This failure to thrive is due to a combination of extra energy required to form a shell (due to lack of necessary ions in the water now bound by acidic molecules) and possibly even dissipation of the fragile shells themselves.

Seed production in the Pacific Northwest plummeted 80% between 2005- 2009, with majority of the larvae dying within merely 2 days. To put into perspective how problematic this is the shellfish industry in this region contribute more than $250 million dollars to the economy annually and provides jobs for over 3,000 individuals. Parallel studies have started on the East Coast comparing conditions and bracing for future ocean acidification catastrophes. New Bedford, Massachusetts, is a major American port with shellfishing making up over 70% of its productivity, so job losses and community demographics would irreparably change for the worse if it is subjected to the consequences of ocean acidification like the Northwest Pacific has.

There has been much active research studying the mechanisms of spat failures and possible ways to rectify this problem both short and long term. One example is Bodega Bay Marine Lab of UC-Davis working with Hog Island Oyster Company based in Tomales Bay, California. Hog Island raises their oyster spat in different water conditions in order to see the effects of various water quality scenarios, including excessive rain, water run-off, on the seed. The seawater of these tanks can be modified in real time if shell degradation is observed and documented for future hatcheries. Bodega Bay Marine Lab in turn records these fine scale aquatic changes in real time. It models how projected increased acidity will affect oysters and other shellfish in 10, 50 and 100 years in the future, and also how possible adaptations to counteract these caustic circumstances could help or hurt the oyster harvests.

Many of these susceptible oyster farms in the Pacific Northwest are multi-generational, family run companies who have to quickly troubleshoot this regional (and imminently global) disaster by changing techniques, importing spat, and monitoring water chemistry in order to adapt. One family, the Taylors of Shelton, Washington, have a separate oyster hatchery prior to planting in the Puget Sound. Hatcheries have been forced to incessantly monitor the incoming seawater acidity and either shut down flow is the water is too corrosive or add seagrass or sodium carbonate to help neutralize it more. This is a drastic change of how these companies have done things historically, but these alterations are a necessity in order to adapt to the changing seawater.

This, however, is just a stop gap. Models predict that corrosive water will be more prevalent at the sea surface and ubiquitous, up to 150% more, by the end of the century. The oyster harvest in the Northwest Pacific could increase by 25% over the next 50 years. This area is the canary in the coal mine- it is the first to show effects of increased acidification and gives insight on the dynamics of how these sensitive ecosystems will react. There are many short and long term strategies being constructed in attempts to rectify the situation, especially because of potential devastating consequences rippling up the entire food web. This research alone, costs from tens to hundreds of million dollars to complete. It is not cheap researching this evolving problem due to fossil fuel emissions; however, losing any of these shellfishing stocks would be detrimental on a much larger scale and immeasurable effects to local economies.

Thank you to OCEAN Researcher Brigid McKenna