Although trophic cascades may be present in stationary food webs, their effects are often seen most clearly after a perturbation. For example, sea otter (Enhydra lutris) overexploitation in Alaska led to population explosions of their sea urchin prey and kelp forest overgrazing (Estes & Palmisano 1974). This ecosystem transformation altered productivity, species assemblages, and coastal erosion, and reversed only once sea otters recovered (Estes & Duggins 1995). Trophic cascades have been repeatedly demonstrated in kelp forests (Estes & Palmisano 1974), lakes (Carpenter & Kitchell 1993), streams (Power 1990), and rocky intertidal ecosystems (Menge 2000).