Restriction of Feeding
Because little sediment accumulates in
the rocky intertidal, deposit feeders are
rare. Most of the sessile animals are filter
feeders. They are unable to feed when
the tide is out. For one thing, they have
to be under the water to filter it. Further-
more, many of them “clam up” during
low tide to avoid water loss and can’t ex—
tend their filtering or pumping appara-
tuses with their shells closed.
Even animals that are not filter feed-
ers have trouble feeding at low tide.
many mobile animals the rocky inter-
tidal are grazers that scrape algae, bacte-
ria, and other food from the rocks.
Others are predators and move over the
rocks in search of prey. At low tide these
animals seek shelter or clamp to the rocks
to avoid water loss. This prevents them
from moving around to find food.
Being unable to feed when the tide is
out is not much of a problem for animals
that live low in the intertidal they still have
plenty of time to feed since they are immersed for most of the day. Higher in the intertidal, however, animals may not be.
underwater long enough to get adequate
feeding time. This may cause them to grow
more slowly than they would with more
time to feed. It may even prevent them
from living in the high intertidal at all.
Many intertidal animals are unable to feed
when exposed at low tide. This may prevent them
from living higher on the shore than they
do.