Swimming footballs

Until you look closer, barnacles come off as some of the least charismatic animals alive. Sometimes it’s hard to believe that those sharp pointy things scraping me as I clamber through the intertidal zone are in fact animals. Barnacles are glued to the rock and unable to move to new locations (locomote) and locomotion is perhaps the most obvious way to tell if something is an animal rather than a plant, fungus, or inanimate object.

Acorn barnacles splashed by waves on San Juan Island, WA

To be honest, barnacles can in fact locomote. However, it is only the larvae that do so. The adults are truly glued and can’t move anywhere but the tiny larvae can disperse far away from their parents by swimming into different ocean currents. When a brooding barnacle releases babies, they emerge as a nauplius larva. The job of this nauplius is to feed and grow until it is big enough to transform into the next larval stage, a football-shaped thing called a cyprid. The job of the cyprid is to find a good habitat to stick to and metamorphose into the adult barnacle form. Today I will focus on these football creatures, leaving the nauplius for another post.

Clusters of gooseneck barnacles (Pollicipes polymerus)on San Juan Island, WA

Cyprids are non-feeding larvae. This means that they do not and cannot feed, even if offered the tastiest feast imaginable. They simply lack the ability to feed. Instead, they carry around energy in the form of oil droplets (fat) that must last them until they settle in an adult habitat and metamorphose. This allows the cyprid to focus on a single job – finding a good place to settle – which is perhaps the most important decision in the life of a barnacle. If the cyprid chooses somewhere far from good food, close to predators, or far from other barnacles, it is unlikely to live very long or reproduce.

A gooseneck barnacle (Pollicipes polymerus) cyprid from Bodega Bay, CA. The big black dot is the eye. This cyprid is about 1/2 mm long. Photo credit: Erin Satterthwaite.

So how does a cyprid find a good habitat? If you think about it, the most reliable cue that a spot along the shore is a good place to live would be the presence of living barnacles of the same species. If they're still alive, it can't be too bad, right? Many species of barnacles, including the gooseneck barnacle featured in this post, are sensitive to the smell of other barnacles of their species. When they detect this smell they will make the critical decision to settle, glue themselves to the rock, and begin the process of metamorphosis.

Close up of adult gooseneck barnacles (Pollicipes polymerus) on San Juan Island, WA.

There is a surprising amount of research on exactly how barnacles decide on a place to settle, more than I can summarize in a short post. The reason for this interest is the issue of biofouling, where marine organisms, including barnacles, attach to the undersides of ships, increasing drag and slowing the ship, which results in higher fuel costs. Biofouling is estimated to cost the shipping industry and navy billions of dollars per year in increased fuel costs and hull cleaning. With an understanding of exactly how barnacles find a place to settle and glue themselves down, engineers have created hull paints that produce a physical surface or compound that discourages barnacles and other animals from settling or makes it more difficult for them to do so. This is a prime example of how basic research and natural history knowledge (how do barnacle cyprids find a place to settle?) can translate directly into applications (how can I stop barnacles from settling on my ship?).

Cyprid is searching

Smelling, tasting, feeling for

A place to grow up