Ecosystems can “flip” and, as a result of reinforcing feedback mechanisms, “lock” into alternative stable states. Robert Steneck, professor at the University of Maine School of Marine Sciences, studied this process in a kelp-forest ecosystem in Maine for nearly four decades and found two stable states: one dominated by green sea urchins and crustose coralline algae and the other by erect fleshy macroalgae. Come hear the results of his studies.