Bivalve Takeover: Once-Benign Clams Boom after Crab Influx
Milius, S., Science News
In a rare analysis of one marine invader benefiting an earlier arrival, an ecologist says that European green crabs invading a California bay have triggered a population explosion of a previously marginal clam.
The European green crab gobbled up two species of native shellfish, says Edwin D. Grosholz of the University of California, Davis. After considering decades of monitoring data and the results of his recent experiments, Grosholz blames this feast for removing competition that had kept the eastern gem clam in check. This clam had lived in the harbor for 50 years or so, but it's only now replacing the native species.
"The key point is that the results of invasions are not easily predicted," comments James T. Carlton of the Williams College--Mystic Seaport Maritime Studies Program in Mystic, Conn. He says that the new results support toughening of protections against alien species in many places.
Typically, some 90 percent of immigrant species do no obvious harm to their new homes, says Grosholz. Ecologists had put gem clams in that group after the East Coast species hitchhiked to the West Coast in shipments of oysters a century ago. The clams, barely half a centimeter across, have occasionally been noticed for decades in California's Bodega Harbor near San Francisco Bay.
In contrast, the European green crab has long been recognized as a menace to marine systems (SN: 6/13/98, p. …