Figure 19.7 Intertidal succession. (a) On undisturbed boulders in the intertidal zone, communities are dominated by a species of red alga, shown in the drawing on the left. (b) When strong waves overturn boulders, bare areas of rock are exposed and quickly colonized by sea lettuce, shown in the drawing on the right. Sea lettuce initially dominates the bare rock surface, as measured by the percent of the rock covered by the algae. As time passes, crabs begin to consume the sea lettuce, which creates space that allows the red algae to colonize the rock and ultimately dominate the boulder’s surface. Error bars are standard errors.

Data from W. P. Sousa, Experimental investigations of disturbance and ecological succession in a rocky intertidal algal community, Ecological Monographs 49 (1979): 227–254.