Weather Watch

Barnacles and sand dollars

Minnesotan Judy Flatten spends her winters in Cayucos. On most days, she takes long walks along the beach between Cayucos and Morro Bay and is glad to have escaped Minnesota's winter freeze.

This year she observed that countless sand dollars had acorn barnacles attached. In fact, these crustaceans, related to lobsters and crabs, were on every solid surface that was temporarily covered by seawater. She wondered if some sort of plague had struck her beloved beach.

After hearing her story, I contacted Fred Steinert with Tenera Environmental Services in San Luis Obispo. Fred has worked in the field of biofouling for decades. Biological fouling is the attachment of organisms to a suitable surface in contact with water for a period of time.

According to some estimates, over 1,700 species are responsible for biological fouling such as barnacles, muscles and seaweeds. It's an important field of study. A naval historian wrote that one factor that helped the English defeat the Spanish Armada “Invincible Fleet“ in 1588 was the installation of anti-fouling surfaces. In other words, they attached copper plates to bottom of their ships. You see, the copper plates prevented seaweeds and barnacles from settling on the hulls of their ships.

This bit of naval technology significantly reduced drag as the English ships moved through the water, making them faster and more maneuverable than the Spanish craft. Fred has spent decades evaluating different types of surfaces and coatings to significantly reduce biofouling. He often uses square foot test plates to evaluate the effectiveness of coatings. Over the years he's detected significant recruitment of acorn barnacles during the August and September timeframe.

Fred told me, that the last two years have been especially strong in barnacle recruitment, which may have led to Judy's observations of countless reddish white, cone-like structures along the shoreline. Barnacles have an interesting life.

Imagine spending most of your time standing on your head and breathing and eating with your feet. As larvae, they look a lot like small leaf hoppers that move with the ocean currents. When they are ready to make a home, they search for a suitable site, like a sand dollar or a buoy. These barnacles may take days to find an appropriate spot, investigating one space, and then moving to another.

When they find a good location, the barnacle glues itself head-first to the surface, and then begins to secrete calcium-hard plates that encase them. When the tide goes out, the barnacle closes up. As the tide comes in, they open up and their feathery legs filter the water for food and oxygen. I've seen acorn barnacles grow as large as three inches in diameter on the Diablo Canyon wave-rider buoy between cleanings.