Changes in Subtidal Community Structure Associated with British Columbia Sea Otter Transplants

Abstract

Sea otters Enhydra Iutris were re-introduced into coastal waters of British Columbia, Canada, in 1969-1972, after being hunted to extinction In the previous 2 centuries. In 1979, we visited an area where 55 individuals had been seen in 1978, and we made subtidal observations of the abundance and distribution of red sea urchins, other grazers, and kelps. Earlier observations, made in the area before sea otters were re-introduced, confirmed that changes have taken place in subtidal communities since the re-introduction. Where sea otters had been observed feeding, sea urchins Strongylocentrotus franciscanus were scarce and restricted to crevices or beneath boulders, other grazers were scarce, and kelps colonized the bottom to 10-m depths. The algal communities in these areas appeared to be simple downward extensions of sublittoral fringe communities. Where sea otters had not fed, kelps were limited to shallow water by abundant sea urchins. The observed differences between the 2 types of areas are concluded to have been caused by early ellmlnation of sea urchins by sea otters, as reported in Alaska and California. From the pattern of sea urchin abundance in the general area of the transplant, we were able to delineate the feeding range of this small population of sea otters.