Killer Whale Predation on Sea Otters Linking Oceanic and

After nearly a century of recovery from overhunting, sea otter populations are in abrupt decline over large areas of western Alaska. Increased killer whale predation is the likely cause of these declines. Elevated sea urchin density and the consequent deforestation of kelp beds in the nearshore community dem-onstrate that the otterÕs keystone role has been reduced or eliminated. This chain of interactions was probably initiated by anthropogenic changes in the offshore oceanic ecosystem. Apex predators often initiate forces that cas-cade across successively lower trophic levels, sometimes reaching the base of the food web (1). Plant-herbivore interactions vary predict-ably with trophic complexity in such systems, being weak or strong when the number of trophic levels is odd or even, respectively (2). Sea otters (Enhydra lutris) and kelp forest