From the field observations, the team, which also included Brian Silliman from the University of Florida, determined the Asian shore crab took advantage of the moist, shady environment created by the cordgrass and the mussels. In ecological terms, the researchers found a "facilitation cascade." The cordgrass attracts ribbed mussels by giving the molluscs something to attach themselves to as well as a shady spot; the mussels, in turn, give the crabs crevices in which to avoid predators as well as the harsh sun. The cordgrass also provides valuable shade for the crabs.
"It's a moist, stable environment in an otherwise harsh environment," Altieri said. "It's the key to their success, the reason why they're so abundant."
The team found that the crabs' exploitation of their habitat did not crowd out native species, such as the common periwinkle, small crustaceans, blue mussels and barnacles. Indeed, the field studies showed the more invasive crabs, the greater the number of native species.
In other words, the cordgrass-ribbed mussel environment has enough room to accommodate another tenant. "They may be promoting co-existence," Altieri said, "allowing for this ecosystem to absorb a new species."
Previous research suggests the crabs do prey upon juvenile American lobsters, and the Brown scientists also want to study whether the crabs eat other crab species.
The research also seems to highlight the importance of cordgrass to provide shade, a service to species that may grow even more important with warming air and water temperatures forecast to accompany changes in the climate.
|Contact: Richard Lewis|