Scientists have not previously documented such organisms exerting the kind of influence purple marsh crabs do over the way an ecosystem functions, from its actual shape to the interplay between predators and prey. “I have no reason to doubt that climate change will alter species' interactions such that new keystone species emerge,” says Linda Blum, an ecologist at the University of Virginia, who was not involved in the study. But, she adds, the team's conclusion that sea-level rise creates new crab habitat by softening marsh soil is built on “a lot of circumstantial evidence.” She suggests it ...