Personally, I think barnacles are one of the Rodney Dangerfields of the marine world. No, they're not funny comedians... they just don't get no respect! Even the most common field guide to marine invertebrates lists just three species, and completely ignores the one I am writing about today, the thatched barnacle. Barnacles, including this species, are very common members of the intertidal and subtidal communities. About the only time they do get respect is when a tidepooler or angler falls and scrapes themselves on them, or the surge throws a diver into a rock full of them.
Barnacles aren't considered tasty like their crustacean relatives the crabs, shrimp and lobster. However, many decades ago while camped at Little Harbor I did make a stew that included a few while on a survival hike with my students from the Toyon school. My students greatly preferred the steaks they had at the Airport-in-the-Sky when they took another trail from the one I hiked. It must have been a long "detour" since they arrived at the campsite hours after I did.
Barnacles belong to the scientific super order Cirripedia or feather-footed crustaceans. They are so named because they use their "feet," amply equipped with feathery cirri, to trap and "kick" food into their mouth inside the calcium carbonate enclosures they create. Their food consists of plankton and tiny tidbits of organic matter drifting in the water around them. I guess they must think if it's good enough for some of the great whales, it's plenty for these generally tiny critters.
The barnacles are an ancient group, appearing on our planet about 500 million years ago. Charles Darwin, who studied these critters, felt that he might be living in the "Age of Barnacles" because they were so common. The species I'm covering today is a member of the suborder Balanomorpha, commonly called "acorn barnacles." They are classified into species based on the number and arrangement of the calcium carbonate plates that make up their "shell," and the arrangement and structure of their appendages
Barnacle lifestyles usually involve substantial differences between the young and the old. Adults are sessile, living out their lives in a single place attached to hard substrates such as rock . Like many species, including humans, the young are restless and head out to seek their fortunes. They live within the plankton, drifting free in the currents to see "the world..." unless gobbled up by some filter feeder, a fish such as a blacksmith, a whale... or a scientist's plankton net.
Note: parents, the following involves subjects suitable for mature audiences only. This species is sexually mature at about two years... Acorn barnacle mating is quite a "feet..." er, feat. Most are hermaphrodites, containing both male and female organs. Sperm is transferred by the male structure to the mantle cavity and female component of an adjacent individual. Of course this involves a pretty substantial "extension" as I will tastefully refer to it. The eggs are then brooded until they hatch into nauplius larvae that leave on their voyages of exploration, drifting with the currents to new "lands." This species may produce three or more broods in summer releasing up to 50,000 larvae in each one. Later, this larval stage transforms into a non-feeding cyprid larva whose job is to locate a suitable home. Some species do have separate sexes, with the male being of very tiny size compared to the female... kind of like pairing the fat lady and the dwarf in a pre-politically correct circus.
The cyprid larvae looks for a place to settle and develop into the sessile adult form by carefully assessing the available habitats it encounters while adrift. They don't have the services of a real estate agent to assist them, so they rely on their own senses. These include both physical and chemical assessments of the proposed site. They don't have to worry about the schools for their offspring since they leave the "nest" early, or even the local transportation services available to them since they are stationary. When a suitable habitat is identified, the larva then use cement glands in their first pair of antennae to glue themselves to it. The young barnacle develops its shell and looks just like a miniature of the adult.
The thatched barnacle has been assigned to different species by different scientists. In our waters it has been known as Tetraclita squamosa and Tetraclita rubescens. Charles Darwin actually gave it the latter name in 1854. It is found from San Francisco Bay to Cabo San Lucas along our coast. Individuals often exceed an inch (30 mm) in diameter and may even reach two inches (50 mm). These acorn barnacles have only four individual plates in their shell, which appears thatched and reddish in color on the outside. When growing, they depend on erosion of the opening of the shell to increase its size. Adults may live 10 to 15 years... if they are not munched on by predatory starfish or snails, or by me in a seafood stew on a survival hike.
Image caption: Thatched barnacles on rock, close-up showing valves to seal in moisture; the actual barnacle inside the shell and acorn barnacle feeding.
