Dive Dry with Dr. Bill

071: Feather Feet- Barnacles

Many swimmers and snorkelers have felt the pain of encountering this group of invertebrates. Barnacles growing on rocks, pier pilings, floats, boat hulls and other organisms, can inflict bloody wounds when our bodies rub against their shells, especially in heavy surge. I've received some pretty bloody cuts from them. They can also rip wetsuits.

Barnacles superficially resemble marine snails like limpets, and in the early history of biology they were actually classified as molluscs. They are really relatives of the shrimp, crabs and lobster, and belong to the phylum Arthropoda, the most successful group of animals on our planet (you know, ants and roaches). It is estimated that 80% of all Earth's species belong to this group. They have adapted to a wide range of habitats. After observing Mars earlier this summer, I wonder if they have been able to establish there. If NASA discovers water on the red planet. I'd love to be the first to SCUBA dive there to find out. // Young barnacles recently hatched from the egg go through several different larval stages in the plankton. These larvae are often quite numerous in the samples I've taken off Catalina and along the Baja California coast. While drifting in the ocean, they may be dispersed to new areas to colonize (like your boat hull!). When ready to settle, they are able to sense suitable habitat through chemical means. Once they find a home, the barnacle cements its head to the substrate and creates the hard calcium-carbonate shell that protects it.

Barnacles are grouped in the subclass Cirripedia which translates as "feather feet." There are four different groups of barnacles, but most people only encounter the goose (or gooseneck) and the acorn types. Since they are attached to the bottom by their head, the feet can extend through the opening in their shell. The feet have feathery structures on them which capture food particles. Barnacles feed with a characteristic sweeping motion, extending the feet, sweeping the water above the shell and then bringing the feet into the shell to extract any food captured by it. This is repeated many times. In effect they use their feet to "kick" foot into their mouths. My mother would never approve of such table manners!

Goose or goose-neck barnacles are often found on surf-swept shores (like Catalina's Shark Harbor) in association with California mussels. They have a flexible, fleshy "neck" which attaches the hard, protective "valves" covering the animal to the rocks. Although they are hermaphrodites and have both sex organs, these barnacles must mate with another. They mate 3-7 times a year with each individual producing up to a quarter million eggs. Most of the larvae that hatch become food for plankton eaters, but the survivors may live 20 years or more after they settle. In the "dark ages" of biology, a noted authority claimed that geese actually hatched from these barnacles, hence the common name. Just goes to show that scientific knowledge is subject to change as our technology and information base improves!

Acorn barnacle shells are the most common type we encounter. They are somewhat conical in shape looking like small volcanos with a little hole in the middle for the legs to extend through. When the barnacle is withdrawn, protective plates cover the hole. One common species here is the buckshot barnacle. Large "colonies" of these tiny (1/4") barnacles are often seen covered the rocks. When I taught marine biology at Toyon Bay, I used to have my students count the barnacles in 3" and 5" squares at several different levels in the intertidal. They called the lab exercise the "idiot's delight," but it produced some meaningful data. Up to 70,000 individuals may be found in a square meter. This lab was actually featured in a Denver Post story after a group of girls from a school there visited our school for a marine biology program.

Specialized acorn barnacles are also seen growing on the skin of gray whales. There may be hundreds of pounds of barnacles on a single whale, a pittance compared to the whale's 30-40 ton weight. However, the resistance caused by barnacles growing on a boat hull, or covering the boat's prop, can be very significant. I once jumped into my 30' dory to take a friend into Avalon who was running late to catch his boat. I cast off from my mooring and my boat just went around in circles. I hadn't used it for several months and barnacles had completely encrusted the prop!

As Steinbeck and I have said previously, true marine biologists are highly libidinous, licentious, lubricious and lascivious folks (remember your "Word Power Made Easy"). Barnacles are a favorite species of such scientists. Think about it. You have individuals fixed to the bottom and therefore unmovable. Yet barnacles must mate with another barnacle. How do they do it? It is said that the barnacle penis is the largest of any species compared to its body size. And they don't even use Viagra!

© 2003 Dr. Bill Bushing. Watch the "Dive Dry with Dr. Bill" underwater videos on Catalina Cable TV channel 49, 10:00 AM and 5:00 PM weekdays.

Colony of small acorn barnacles on rocks; goose or gooseneck barnacle at Shark Harbor; acorn
barnacles extending their feathery feet to feed; barnacles on the skin of a gray whale's head.

This document maintained by Dr. Bill Bushing.
Material © 2003 Star Thrower Educational Multimedia