Barnacles are very prolific, yet do not seem to get the “cool” designation of other marine life. Emerging from a dive, people ask what did you see? If I reply I saw a bunch of barnacles, their faces tend to fall and they quickly ask “Well, yes, but anything cool?”

What’s up with that?! Probably it’s because barnacles are so prolific, they cover just about everything in the tidal zone. Or maybe it’s because they hurt when stepped on or you got scraped by some while swimming.

Or maybe it’s because they can foul a ship’s bottom or attach themselves to the throat of a magnificent whale or the snout of a cool sea-turtle and make them look low-rent. It has been estimated by the U.S. Navy that barnacle growth on vessels increases drag in the water (and thus amount of fuel being consumed) by more than 60%. Not much barnacle love there!

But maybe we should not be hating on the barnacle so much, because they have actually reached an evolutionary status of simplicity, durability and profusion. One source I found, which celebrates the barnacle, says that they have reduced themselves to the barest necessities of life.

Rough barnacles are attached to an iron bar off Owls Head. Photo by Charles H. Lagerbom.

Here in Maine waters, two kinds of barnacles proliferate. The Common Rock Barnacle (Balaunus balanoides) is a small, cone-shaped shell very rough on the outside. Its cousin, the Large Rock Barnacle (Balanus balanus) is obviously bigger, over an inch or more in diameter. Plates of large rock barnacles fit together in a different pattern than the common rock barnacle, which is how you can tell most of them apart.

Barnacles even have their own zone in the sea named after themselves, the Barnacle Zone, one of six general zones on the rocky shore. Wicked hardy critters, barnacles can withstand more extremes of exposure than any other animal along New England’s coast. Winter cold, summer heat, pounding waves and long exposures not submerged have made barnacles the tough little customers we see on Maine shores.

Barnacles are little crustaceans that adhere themselves to rocks, hard surfaces, and sometimes other marine life. They are a type of anthropod, therefore related to crabs, lobster and shrimp and are exclusively marine.

The study of barnacles is called cirripedology. That is because their feeding limbs are called “cirre.” The interesting part here is that the barnacle basically lives its life upside down.

The free-swimming larva have cement glands in their heads that form the base of their first set of antennae. So, the critter will affix itself to the substrate by its forehead. A ring of plates surrounds the body, which I think makes it look kind of like a tiny volcano!

Inside the plates, the animal lies on its stomach, with its limbs projecting upwards or upside down. From there, the barnacle is not much more than a mouth, a digestive tract and eight pairs of legs.

Considered sessile, they are filter feeders. The eight pairs of thoracic limbs called cirre, are feathery and very long, and used to filter food, such as plankton, from the water and move it toward the mouth. They basically eat with their legs while standing on their heads. Barnacles feed on plankton and dead organic material, pretty much anything they can grab.

This barnacle is attached to a mussel shell at Rockland Breakwater. Photo by Charles H. Lagerbom.

Barnacles have no true heart but there is a circulatory pattern. Three photoreceptors help the barnacle show reflex. A sudden decrease in light will stop their feeding, the cirre will withdraw and the volcano-like shell will close up with an opercular plate. They can easily batten down the hatches, until they once again feel safe to reopen.

When the tide goes out, barnacles shut their operculum to retain moisture and can thus survive in areas that remain dry up to 70% of the time. During winter, many do not feed, but simply rely on energy reserves.

A fertilized egg hatches into what is called a Nauplius, a one-eyed larva with a set of horns. After six different moults, it becomes a Cyprid larva, the largest larval stage before adulthood. This “teenager” phase is not a feeding stage at all, but one in which the barnacle seeks out its place to adhere. It is an important phase; they need to choose wisely since their cemented connection will be for life.

Once attached, the barnacle becomes a juvenile and then grows by adding to its six calcareous plates that surround it. This takes about half a year for them to reach adulthood and then two years to become sexually mature.

Barnacles are hermaphroditic; they carry both ovaries and testes, but self-fertilization rarely occurs. Being cemented upside down makes sexual reproduction a challenge for them. Barnacles tend to reproduce in one of two different ways.

One is called sperm-casting, where gametes are released into the water to be picked up by others nearby to fertilize their eggs. Kind of a shot in the dark hit-or-miss process.

The other way is to use their extremely long phallus on a nearby barnacle. Barnacles probably have the largest “member” to body size ratio of the entire animal kingdom. It is up to eight times their entire body length. Whoa!

Either way, the job gets done and fertilization occurs. Barnacles have been found as deep as 2,000 feet, but most generally live at much shallower depths. Fully one quarter of all barnacles live in the intertidal zone.

Clusters of barnacles are found at Duck Trap Harbor. Photo by Charles H. Lagerbom.

Barnacles compete with limpets for places to adhere to and have numerous predators, especially whelks and mussels. One way to protect their species is to swamp an area with lots of their kind; thus percentagewise, many should survive.

The other strategy is called fast growth, which allows them to resist encroachment of their territories by a quick turnaround from juvenile to mature adult. The race is on to cover an area before that limpet family arrives!

Some barnacles are considered edible, most notably Japanese goose barnacles, which are a delicacy in Spain and Portugal. But overall, I find that people do not generally care for the barnacle.

So, let’s all throw those barnacles a little love, since they are pretty hardy survivors of the ocean and have learned to stick with it! (Sorry!)

Charles Lagerbom teaches AP US History at Belfast Area High School and lives in Northport. He is author of “Whaling in Maine” and “Maine to Cape Horn,” available through

filed under: