A starfish which is an important predator in the rocky intertidal communities of the American Pacific Coast is

In the rocky intertidal communities of the American Pacific Coast the starfish Pisaster is an important predator. In a field experiment, when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year, because of interspecific competition. Hence, it is a keystone species too.