|Why can we not see the barnacle animals?
|Question Date: 2001-03-06|
Barnacles, like many other sessile intertidal
invertebrates are filter feeders and comb the
water for planktonic food when the tide is in.
The class to which barnacles belong, Cirripedia,
means "feather-foot". These creatures stand on
their heads and filter-feed with their feet. When
the tide is out (when you are most likely to go
"tide-pooling"), they retreat into their
protective "houses" that they, themselves,
fabricate. These "houses" are permanently bound
to the rock surface, so they can not move about to
escape the sun at low tide. Barnacles have soft
bodies, so if they were unprotected during low
tide, they would quickly dry out and perish. When
the tide is out, the barnacle retreats into its
"house" and protective calcareous plates seal the
apical opening, preventing water loss. When the
tide returns, these plates retract and the animal
is again able to filter feed.What you observe at
low tide is the sealed protective "house" with the
barnacle animal safely inside.
Barnacles are indeed interesting animals. Could
you imagine spending most of your life standing on
your head and eating with your feed?! Sounds like
a difficult way to get through the day? Well,
that's exactly how barnacles spend most of their
If you walk along the sea shore, you
can find barnacles on almost any solid surface
that gets covered by water. On rocks, dock
pilings, boats, even mussels, you can find
clusters of these hard, white, cone-like
houses.That's where barnacles live, peeking out
only when water covers them so they can filter
food into their homes. This "barnacle zone" is the
highest of the intertidal zones.
When you go
to the tide pools you normally go at low tides.
These are also the times when the barnacles are
not covered with water and therefore have their
house closed to stay wet inside. That's why we can
not see them.
That's a good question! Sometimes when we go
tidepooling there are no barnacles. Sometimes,
there are barnacles but they are hidden. When
barnacles are hiding it is because they are trying
to protect themselves. Why would they do that
Jorge? Do you know? Can you or any of your
O.k. I will tell
you. Maybe you or your friends guessed right.
Barnacles need to protect themselves from the
sunlight and the heat of the sun, and from the
waves that crash all around them. Next time you go
to the tidepool, try to find a pool full of lots
of cold water and look in it. If you watch for a
while, I bet you will see a barnacle feeding! It
is not hiding because the tidepool is so
comfortable that is can eat (a scientist would say
the condition of the tidepool is good for
feeding). BUT...if there are big waves or a hot
sun shining down hard on it, then the barnacle
stays in its shell, and waits until the
"conditions" are better.
IF you go to a
tidepool and there are no barnacles, it might be
because the water is too rough or because other
things live there that don't like living with
barnacles and try to keep them out. But usually
there are barnacles, and maybe you just can't see
them because they hide themselves so well.
The barnacle animal cannot get dried out or it
will die, therefore, it closes off the top of its
protective covering when the tide goes out and the
water no longer covers it. It does this so it can
keep its moisture at a constant level. When the
tide goes out the barnacle can also no longer feed
(which is does through that opening too), and
lastly, the barnacle animal is vulnerable to
predators when it is open, so when the tide goes
out it also needs to protect itself from hungry
seagulls and nosy dogs!
Some barnacles are gooseneck barnacles, and they
stick out quite a way and pull in when you make a
shadow over them. But their front ends are covered
with shell-like plates, so maybe they're not
letting us see them.
I guess barnacles are
safer in their shell, because it's hard to eat
them. They're probably too dumb to know or care
whether we see them or not, because they don't
have a brain. I think I remember learning that
they have a nerve net instead of the huge clump of
nerves we have in our brain and more nerves in our
spinal chord and all through our bodies.
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