Can Shellfish Adapt to Ocean Acidification?

In the Pacific Northwest, oyster aficionados have likely tasted Chris Langdon’s scientific handiwork. Since 1996, his Molluscan Broodstock Program at Oregon State University has been breeding plump, fast-growing, and hardy oysters as stock for the $250 million West Coast oyster industry. But in the past several years, the program has taken on an additional goal: identifying oysters that are more resilient to ocean acidification. In 2007, oyster hatcheries in Oregon and Washington began experiencing massive die-offs of their larvae that continued for several years. Eventually, managers and scientists realized that the larvae were dying during periods of strong upwelling, when deep waters rich in CO2and low in pHcome to the surface. These deep waters were even more acidified than in the past because of the oceans’ growing uptake of CO2 as its levels in the atmosphere increase. When CO2 dissolves in water, carbonic acid forms, releasing hydrogen ions that lower pH and convert carbonate ions to bicarbonate. The corrosive upwelling in 2007 dropped carbonate levels in the seawater enough that aragonite, the main form of calcium carbonate bivalves use to build shells, became undersaturated. Langdon and his colleagues showed that aragonite undersaturation ultimately drives oyster larvae to make smaller shells than usual or not to develop them at all. Both can spell death. Scientists, including Langdon’s colleague Burke Hales, quickly began working with oyster growers to monitor carbonate chemistry in hatcheries and to buffer the water with sodium carbonate when aragonite became undersaturated during upwelling episodes. In 2010, the National Oceanic and Atmospheric Administration sponsored a $500,000 network of six monitoring systems at West Coast hatcheries. Since 2011, this intervention, though costly, has helped avert major larval die-offs, Langdon says. But the experience made it clear that ongoing ocean acidification, which threatens marine organisms ranging from certain plankton at the base of the food chain to shellfish and corals, could endanger the shellfish industry worldwide. Fortunately, there is evidence that some shellfish may be able to acclimate or adapt to these changes, thanks to the variable conditions these creatures experience and the wide genetic variation among individuals in a given species. As intertidal species, oysters see a lot of environmental change even on a daily basis, says Steven Roberts, a fisheries scientist at the University of Washington, Seattle. In an effort to identify hardier shellfish stocks, Langdon, Roberts, and many other researchers are looking to determine the genetic and metabolic underpinnings of adaptability to acidification. They are on the hunt for biomarkers that could eventually help shellfish growers select more resilient stock or adjust hatchery conditions for improved survival and growth. Langdon was inspired by University of Sydney researcher Laura Parker’s work showing that stocks of the Sydney rock oyster bred for aquaculture grew shells better than wild oysters under acidified conditionssuggesting that the species has the genetic potential to adapt to acidification and that selective breeding for good hatchery performance could be a key to this. But Langdon’s first attempt to repeat this experiment with his own stock of Pacific oysters from the Molluscan Broodstock Program did not show the same advantage. So he and his colleagues are now testing the survival of a variety of different farmed oyster stocks at an acidified pH of 7.8, similar to that found during upwelling, and