Kelp Beds and Sea Otters: An Experimental Approach

A rapid and extensive modification of algal species composition and a dramatic increase in kelp biomass follow the return of sea otters, a once common (but now absent) sea urchin predator.

Abstract

In Torch Bay, Alaska, USA, sea urchins structure shallow subtidal communities by consuming most macroscopic algae. Experimental removal of urchins leads to the development, within 1 yr, of a kelp association of high biomass and diversity. In the 2nd yr, however, these attributes decrease as a single kelp species, Laminaria groenlandica, becomes dominant. Additional field experiments confirm the competitive superiority of this kelp. These manipulations lead to predictions regarding the ecological role of sea otters, a once common (but now absent) sea urchin predator. The predictions are tested and verified by examining areas into which sea otters have recently been transplanted. As expected, a rapid and extensive modification of algal species composition and a dramatic increase in kelp biomass follow the return of sea otters.