Mussel beds and seaweed stands as alternative communities on rocky intertidal shores

Welcome!
One of the most vexing problems in ecology is how distinctly different communities, such as mussel beds and seaweed stands, can occur in the same ecosystem. These communities often persist for long periods, yet small shifts in environmental conditions can cause an unexpected tipping of the system and seaweeds may be replaced by mussels, or vice versa. How can alternative communities be both persistent and yet so susceptible? The theory of these systems, known as multiple stable states, is well understood, but whether multiple stable states actually exist in nature has remained a hotly debated subject and, not surprisingly, definitive examples continue to be elusive. This web site provides an introduction to a long-term ecological study of mussel beds and seaweed stands on rocky intertidal shores in the Gulf of Maine as a test of the theory of multiple stable states.