Kelp communities and sea otters: keystone species or just another brick in the wall?

Abstract

Observations at sites in the NE Pacific have led to 2 generalizations: 1) kelp communities on nearshore, subtidal reefs exist in one of 2 stable states, forested with few large sea urchins or deforested with abundant large sea urchins, and 2) changes of state are controlled by a keystone predator, Enhydra lutris. Sea urchin grazing effects can be highly variable in the absence of sea otters; deforestation by sea urchins is the exception (<10% of the sites surveyed). Also, the communities do not exist in 2 states controlled by otters, but rather exhibit a dynamic range of composition where the above "states' are the uncommon extremes. The keystone species hypothesis is rejected as a geographic generality for the control of kelp community structure in California and perhaps elsewhere. -from Authors