Animals and plants that are innocuous in their home environment can become rampaging pests when they invade a new area. A new study shows that for a wide group of marine pests, invasion is coupled with a marked increase in body size.

Edwin (Ted) Grosholz, a cooperative extension specialist in environmental science and policy at UC Davis, and Gregory M. Ruiz of the Smithsonian Environmental Research Center in Edgewater, Md., compared body sizes of 19 species of marine and estuarine invaders including crabs, shellfish and starfish in their native habitat and in other parts of the world where they have become invasive pests.

Twelve of the 19 showed increases in maximum size of up to 40 percent. European green crabs and Chinese mitten crabs, both prominent nuisance species in U.S. waters, were about 20 percent bigger than in their native habitat. Only one, the gem clam, showed any sign of a decrease.

The increases in body size were not clearly linked to differences in latitude between the native range and invaded areas or to the length of time since invasion. The changes could be because the animals are no longer held back by predators or parasites, Grosholz said.

The findings, which are published in the journal Ecology Letters, could have implications for understanding both how modern-day nuisance species become successful, and for interpreting fossil evidence of changes in populations of marine animals over millions of years.