It wouldn't take much. "Introduced species can spread throughout entire ecosystems and across biogeographical regions from a few individuals released at single sites," say John Chapman and Todd Miller of Oregon State University's Hatfield Marine Science Center in Newport, and Eugene Coan of the California Academy of Sciences in San Francisco in the October issue of Conservation Biology.
While some of the non-native species sold in Pacific Northwest markets are already established or cultured in local waters, many are not. "Their unplanned, unsanctioned introductions should be controlled or avoided," say the researchers. Invasive marine species are environmentally and economically costly. For instance, the European green crab costs an estimated $44 million per year in mitigation expenses and fisheries losses in northeast Pacific waters.
Chapman and his colleagues focused on trade in clams, mussels and oysters. These bivalves can survive out water for more than two weeks when refrigerated, and are usually mature when sold. This means that "fresh" bivalves sold at markets might be able to spawn if returned to marine waters.
To test whether the live seafood trade could indeed spread non-native bivalves, the researchers assessed whether three non-native species sold in Pacific Northwest markets were still alive enough to feed a day after being returned to seawater. Spawning can be triggered by eating, stress or sudden temperature changes. Two of the species (Manilla clams and Pacific oysters) are already established in Pacific Northwest waters but one (the ocean quahog) is not.