Pisaster is a keystone species without which 10 invertebrate species were extinct. Which of the following is correct with regard to this statement?

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.