9529564 Petraitis The goal of this proposal is to determine the ecological mechanisms that maintain stands of algae and beds of mussels and barnacles in the Gulf of Maine as distinct, self-sustaining communities. Mussels, barnacles, and macroalgae are the most common species on the rocky intertidal shores of sheltered bays. As the major structural components of the natural communities that line the shore, these species are the home for many species of fish and invertebrates. Stands of rockweed and beds of mussels and barnacles are distinct and rarely overlap even though they occupy very similar places on the shore. Currently, it is thought that local site-specific differences in ecological processes such as predation, competition, and recruitment, control the species composition of these two communities. This research project will test the idea that the origins of algal stands and mussel-barnacle beds are historical events and that once established, the two distinctive communities are maintained by positive-feedback mechanisms within each. Thus local site- specific differences are the result of positive-feedbacks and not the cause of community differences. In ecology, this idea is generally known as "alternative stable states." This project will be the first large-scale test of this idea in a coastal marine ecosystem.
