Barnacles: Sticky Crustaceans Explained

barnacle facts
Northern rock barnacles (Balanus balanoides) are a common acorn barnacle found in shallow waters along the northern Atlantic Coast.

AS ANIMALS THAT SPEND THEIR LIVES HIDDEN INSIDE HARD, PROTECTIVE SHELLS, IT’S EASY TO OVERLOOK BARNACLES. In fact, they may be subtle but they’re fantastic, busy little guys, always working the plankton for edibles. Need evidence? Here are some random barnacle facts.

1  Acorn and gooseneck barnacles are both crustaceans in the cirripedia subclass – cirripedia reflecting their singular adaptation of their legs into cirri used for capturing prey.

2   They’re the only crustaceans that are sessile – they attach themselves permanently to substrates as varied as granite boulders, dock pilings, ship hulls, clam and oyster shells – and whales and turtles. Some species are known to bore into hard corals. It’s not unusual for goosenecks to cement themselves to other gooseneck shells.

barnacle facts
Sporting a single, large barnacle on its shell, this Hawksbill turtle forages in the Philippines.

3   Acorn barnacles glue their calcareous castles directly to their host surface. Gooseneck barnacles float above the surface, tethered by flexible stalks. Acorns do so with a system of plates surrounding them, topped with moveable plates that serve as ‘doors” through which they extend their cirri.

4   Gooseneck barnacles are often described as occupying paired plates in a flattened oval envelop, atop their gooseneck stalks.

5   Barnacles fasten themselves to their host surfaces with a glue produced by glands at the base of their antennae. On goosenecks, the glands are at the base of the stalks, which are part of the barnacles’ heads.

5   Barnacles are found worldwide in pretty much every environment, from arctic seas to tropics, deep ocean to shallow waters (although they’re most often shallow).

6   With some 1,200 species spread out all over the world, common names and even species I.D.’s vary all over the place but they’re all generally referred to as “gooseneck barnacles.”

7    Like all crustaceans, as barnacles grow, they shed their chitinous exoskeletons for new ones. Unlike other crustaceans, they also need to enlarge their limestone castles. It’s not clear how they do this but it’s suspected that as they add new outer layers they secrete chemicals that thin inner layers.

8   Barnacles are well-endowed – it’s believed some species have the largest penises compared to body size of any animals. And they need them, since they mate by extending their penises into the mantle of neighboring barnacles.

9   Since they do so without leaving their own shells, a requirement for successful continuation of the species is that they live close to each other, generally no more than inches apart. They’re hermaphroditic – they have both male and female genitalia – but they mate with neighboring barnacles.


barnacles facts
Gooseneck barnacles have a tendency to glue themselves atop the shells of other goosenecks.

10   Barnacles are subject to predation from a variety of animals, including whelks and sea stars. But a major issue for barnacle survival is competition for space, both with fellow barnacles and mollusks like limpets and mussels.

11   Charles Darwin is famed for developing theories of evolution based on Galapagos finches, but before he published his revolutionary (and evolutionary) work he spent years studying barnacles to better understand the nature of species. Much of our understanding of barnacles comes from his work.

12   Barnacle cement is one of the strongest substances known – a layer of the stuff only three thousandths of an inch thick can handle a weight of some 7,000 pounds. And it’s durable through intense heat, acids and other substances. Scientists are trying to unravel its secrets for use in dentistry and bone surgery.

13   On the other hand, barnacles that find their way onto ships’ hulls can slow them down significantly. It’s estimated that the shipping industry spends more than $100 million annually to de-barnacle ship hulls.

14   It’s estimated that barnacles live anywhere between one and six years. Body sizes range from an inch or less to several inches.

15   Nobody is likely to go out to the New England coastline and start collecting northern rock barnacles for dinner, but in some cuisines gooseneck barnacles are considered a delicacy.

PRINCIPAL SOURCES: Crustacea Guide of the World, Helmut Debelius; Peterson’s Field Guide to the Atlantic Seashore, Kenneth L. Gosner; “Barnacles,” Woods Hole Oceanographic Institute; “Lepas anatifera,“Semibalanus balanoides,” Animal Diversity Web, University of Michigan; “Biology of Barnacles,” Museum Victoria Australia; “Barnacle,”