Barnacles
Order: Sessilia

Barnacles are small, grayish-white crustaceans that live on rocks, pilings, boat hulls and other hard surfaces throughout the Chesapeake Bay.

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Barnacles live on rocks, reefs, jetties, pilings, grasses, boat hulls and other hard surfaces in shallow waters. (Nathan Acks/Flickr)

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Appearance

Four species of barnacles can be found in the Chesapeake Bay

  • Bay barnacle, Balanus improvisus
  • White barnacle, Balanus subalbidus
  • Ivory barnacle, Balanus eburneus
  • Little gray barnacle, Chthamalus fragilis.

Barnacles vary in size from less than half an inch to 1 inch in diameter, and have six overlapping grayish or whitish shell plates. They have a flat base and an opening at the top that has two valves that open and close like "trap doors."

Feeding

Barnacles feed while submerged underwater. The barnacle’s “trap doors” rhythmically open and close, and feathery appendages emerge to collect and sweep in tiny food particles such as plankton and detritus.

Predators

Barnacle larvae are an important food source for young fish in the spring. Flatworms are major predators of adult barnacles. Sponges, bryozoans and similar animals can grow on top of barnacles and smother them.

Reproduction and life cycle

Spawning occurs in mid- to late spring. Each barnacle has both male and female organs, but eggs must be fertilized by another barnacle. A sperm tube extends from one barnacle into a neighboring barnacle to fertilize its eggs. Once the eggs hatch, the barnacle releases tiny larvae into the water.

Larvae go through two stages, each lasting a few days. Second-stage larvae search for a suitable hard surface to attach, usually among adult barnacles of the same species. Larvae attach themselves to a hard surface using a cement-like substance secreted from a special gland. After attaching, larvae develop shell plates that eventually cover their body.

Did you know?

  • Although barnacles look like empty mollusk shells, they are actually crustaceans that are related to crabs and shrimp.
  • They are sensitive to very cold or dry weather.
  • Barnacles grow by adding calcium carbonate to the edges of their shell plates. The interior of the barnacle grows by shedding its exoskeleton, just like blue crabs and other crustaceans molt.

Sources and additional information

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