The Barnacle

More Than Meets the Eye

By Tasha Smith, Leigh Calvez, Deb Rudnick

Photos &  video by John F. Williams except where noted

The Barnacle

More Than Meets the Eye

By Tasha Smith, Leigh Calvez, Deb Rudnick, Autumn 2018

Photos &  video by John F. Williams except where noted

My first experience with barnacles came during a field trip for a marine biology class in junior high. We visited a local marine museum and then went outside to the nearby marina to an area where no boats were moored. We all lay down on our stomachs and looked over the edge into the water at all the marine life clinging to the side of the dock. I had the perfect view of barnacles in action. From hard, circular pyramid-shaped shells, six pairs of feathery, olive green legs, swept through the salt water around them, feeling for a meal. Seeing the barnacle moving like this, I realized, there is more to these organisms than meets the eye.  

At first glance barnacles look much like mollusks with shells like clams and oysters. In fact, they are classified as crustaceans and are more closely related to crabs and lobsters. There are currently about 1,220 known species of barnacles around the world, ranging in size from about a half inch to nearly three inches across. Most barnacles live from five to ten years with a few of the larger species living up to twenty in the tough intertidal zone, battered by waves and seared by the sun.

Barnacles live their lives in three stages, two larval stages during which they are free swimming and one adult stage, solidly anchored to a surface and living in colonies closely surrounded by neighbors. They are hermaphroditic and so, are both mother and father to offspring. Usually when the water temperature and the season is right, they extend an extraordinarily long penis over to a neighboring shell to deliver their sperm. The receiving barnacle holds the fertilized eggs until they develop into minuscule, alien-looking creatures with translucent body, feathery appendages and two, short antennae. Then larvae are released into the ocean where they swim and grow. As crustaceans, the nauplius larvae have hard shells and undergo a process known as molting, as they shed the old shell to grow a new one. After several molting cycles, the nauplius larvae grows into its next stage, a cyprid larvae. 

Movie by Tasha Smith, “I had the perfect view of barnacles in action. From hard, circular pyramid-shaped shells, six pairs of feathery, olive green legs swept through  the salt water around them, feeling for a meal.”

In this stage the young barnacle has only one job—find a place to live. The cyprid will refrain from eating, as it has limited room to grow. It also has the ability to detect and recognize other barnacles of the same species. It uses this sense to search around for the right place to call home, any hard surface such as a rock, buoy, piling, the hull of a ship, or even a whale. Some species of whales, like humpbacks, gray whales and right whales carry up to a ton of barnacles.

Once the barnacle finds the right place, the cyprid will secrete a special cement-like substance to attach itself to a rock. The cement is so strong it can hold 22-60 pounds per square inch! In fact, scientists are trying to recreate it for use in dentistry and bioadhesives for medical implants and micro-electronics. Before permanently attaching itself, the cyprid molts once more and rotates so that its appendages are facing upward. Then the barnacle attaches its head to the surface in a permanent headstand.

Excerpt from the movie, Exploring at Low Tide, citation below in “Find Out More”

Once attached to a surface the barnacle begins to build its shell. The surrounding shell is composed of six calcium plates, plus there are two to four plates that act as doors. During low tides or when threatened they are able to close those doors creating a nearly impenetrable fortress. Over time they do grow and add to those plates as they expand in size.














































Barnacles with plates that have progressively color coded to illustrate the structure of the different plates. (The color coding was done in a computer, not on the barnacles themselves — no barnacles were harmed in the making of this illustration)
These barnacle sculptures by Ike Eisenhour show how the barnacles’ outer shells are made of interlocking plates. Limpets are often found near or on barnacles.  See link under “Find Out More” below. Photo by Ann Welch

Another kind of barnacle, the gooseneck barnacle, is found in less protected areas like the Juan de Fuca Strait and Pacific coastal beaches. Gooseneck barnacles have a stalk which allows the barnacle to attach itself into deeper crevasses in rocks, while the shell extends out from the rock on the stalk.

Barnacles that we see on the beach are covered by water at high tide, and they are exposed at low tide. Barnacles cannot live higher on the beach than the high tides reach. Because of this distinct upper limit where they can exist, identifying barnacle populations, either in photographs or as fossils, has been used in some places to track sea level changes over time.

Barnacles are generally more active at night than they are during the day. This is because their food source, zooplankton—tiny, free-floating oceanic animals—come toward the surface at night. During daylight hours zooplankton spend their time in the darker depths. The barnacles catch the zooplankton by waving their feathery legs, called cirri, around through the ocean water.

As we’ll see in articles in this and other issues of Salish Magazine, the creatures we visit are not isolated lab specimens, they are part of complex ecosystems. They interact in a variety of ways with other creatures and with inanimate things such as rocks and currents. This video illustrates some of their interactions, including abandoned barnacle shells being used as a nest for fish eggs.

Excerpt from the movie Return of the Plankton. Citation is below under “Find Out More.”

Barnacles are food for several marine organisms. Whelk is a general name given to a category of snails that routinely patrol areas where barnacles exist. The area between the inner and outer plate of the barnacle has proven to be a weak spot, so the whelks target this weakness to access the meaty inside. Other times whelks drill through the outer shell to get to the inside. Sea stars also eat barnacles by using their feet to pry open the barnacle plate to access the inside. Once they open the barnacle, sea stars are able to eject their stomach outside of their body to consume the meat.

Humans also eat barnacles. In Spain and Portugal, the gooseneck barnacle is considered a delicacy. One barnacle can cost at least $2 and if you have a plateful it can get expensive quickly. The barnacles are prepared by boiling them in seawater with onions, lemon, and bay leaves, then served cold, often with lettuce, slices of lemon, aioli or garlic butter, much like escargot.

The gooseneck barnacle is native to the Pacific Northwest and is often harvested here and shipped to other countries to be consumed.

Some consider barnacles to be pests. When too many barnacles build up on the hull of a ship, it slows the vessel down by creating drag, causing the vessel to burn more fuel which increases the amount of greenhouse gases produced. Research is ongoing to create environmentally friendly paints and anti-fouling coatings to prevent “biofouling”, the growth of barnacles and other sea life on the hulls of ships.

Barnacles really are cool little organisms once you get to know them a little better. They’ve adapted to survive in the harsh environment of the intertidal zone, as marine creatures that live out of the water much of the day. Some see them as pests, but I think they are special. Next time you’re at the beach or on a dock, I encourage you to take a few minutes to look around to see if you can find some barnacles. They could be lurking in the tide pools. You never know when you might see some of these little creatures in action.

In Spring, 2018, Tasha Smith was a student at WWU’s Huxley College of the Environment in a class titled “Research of the Salish Sea” taught by Jenise Bauman. Tasha and other members of her class researched and authored articles for this inaugural issue of Salish Magazine.
Leigh Calvez is a naturalist and nature writer. She studied humpback whales in Massachusetts and on Maui, Hawaii along with spinner dolphins on the Big Island of Hawaii. As a naturalist, she has led whale watching tours around the world to places like the Azores, New Zealand and British Columbia. Her interest in the natural world led her to nature writing and her first book “The Hidden Lives of Owls: The Science and Spirit of Nature’s Most Elusive Birds”. Leigh’s essays have appeared in Smithsonian Magazine, High Country News, The Ecologist, Ocean Realm, The Christian Science Monitor, The Seattle Times and The Seattle Post-Intelligencer. Her second book, “The Breath of a Whale: The Science and Spirit of Pacific Ocean Giants,” from Sasquatch Books was released in March 2019.
I need to add Deb Rudnick’s bio and pix here


There is a lot of information about barnacles online, but here are a few resources that are fun, informative and relevant to this article.

Barnacles: Retrieved from

David (Ike) Eisenhour, metal sculptor who creates large versions of subjects from nature.

Loomis SH (1987). A delicacy scraped from Pacific rocks. New York Times. Retrieved from

What are barnacles? Retrieved from

Slater Museum of Natural History. Acorn Barnacle. Retrieved from

WSU Extension and Still Hope Productions (2014). “Exploring at Low Tide” The video clip discussing barnacles settling and feeding was from this movie.