Natural disturbances can have effects
similar to those of predation. When mussel
beds get too dense, clumps of mussels
can be torn away by waves (Fig. 11.12),
exposing the bare rock. Drifting logs that
batter the rocks and, in cold places,
scouring ice and severe freezes have the
same effect of opening up new space.
This prevents mussels from monopolizing
the available space, allowing other organisms
to persist.
When a patch of space is cleared, new
organisms often move into the patch and
get replaced by others in a regular sequence
(Fig. 11.21). The term ecological
succession is used to refer to such regular
patterns of regrowth. In the rocky intertidal
the first stage is usually a thin film of
bacteria and microscopic algae, such as diatoms,
that covers the rock. This film may
condition the rock surface, since the settling
larvae of some species prefer surfaces
with this film to bare rock. Seaweeds often
move in next, followed by barnacles and
finally mussels, the dominant competitor.
The final stage in an ecological succession
is called the climax community.