Acidic ocean spawns wimpy mussels

Increased ocean acidity is taking a toll on mussels, creating a domino effect on coastal ecosystems from Alaska to California. Due to the absorption of carbon dioxide, ocean acidity has increased by almost a third since the 18th century, weakening the shells of California mussels and diminishing their body mass, according to a new study published in the Journal of Experimental Biology. California mussels (Mytilus californianus) spend the first part of their lives swimming freely as larvae, before settling onto rock beds along the western coast of the U.S. from Alaska to California where they grow into adults. More than 300 other species share the beds or depend on the mussels in some way. “Because these mussels play such an ecologically critical role, a decline in their numbers could impact a wide range of other organisms,” says Brian Gaylord, associate professor of evolution and ecology at the University of California, Davis and first author of the paper. In the lab, Gaylord raised mussels from fertilization to the point where they were ready to settle, rearing them in both normal seawater and in water with two different conditions of elevated acidity. The acidity levels were based on projections by the Intergovernmental Panel on Climate Change, a Geneva-based scientific body established by the United Nations. One of the elevated acid levels assumed continued heavy use of fossil fuels; the other assumed a more optimistic scenario. Compared to those raised in normal seawater, young mussels living in the more acid waters had smaller, thinner, weaker shells, and as much as a third less body mass. The weaker shells make mussels more vulnerable to predators like crabs that crush their prey, as well as to carnivorous snails that drill through shells, Gaylord says. Smaller body size make them more likely to dry out at low tide and less able to withstand the energetically expensive process of metamorphosis from a free-living larva to a settled shellfish, Gaylord says. “Together these trends suggest that we’re likely to see lower survivorship of young mussels as they return to shore.” The work was funded in part by the National Science Foundation.