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 lives.
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 friends guess?


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.