To add a few more players to the trophic cascade: The sea otter population has rebounded along the Central California coast, but their spread to Northern Calif

To add a few more players to the trophic cascade: The sea otter population has rebounded along the Central California coast, but their spread to Northern California is limited by shark predation. As a result of the absence of sea otters, north of San Francisco the abalone populations have rebounded. The abalone in turn, compete with the urchins to eat the kelp. There's concern that if the otters spread further north, the abalone population will be decimated. But this raises the question: didn't the otters and abalone coevolve? http://soundwaves.usgs.gov/2006/02/research.html http://soundwaves.usgs.gov/2006/02/research.html