The vertical zonation of organisms on the rocky shore can be further
defined by level of wave action. Wave-exposed shores
are characterized by zones of densely packed organisms and little
open space. Few organisms can tolerate high wave action and so they
dominate these habitats because the waves limit the abundance of
predators. Competition for space becomes the primary
factor in determining distribution patterns of organisms. Yearly
variation in recruitment also affects organism distribution. If there
are not enough recruits settling in the area by one species, another
may take over and in contrast if there are too many recruits, particularly
with barnacles, overcrowding can cause members of a population
to die or leave. It is a delicate balance.
