Barnacles

Barnacles are small crustaceans that vary in color from gray to white.

• Formed by six overlapping plates of shell with a flat base and an opening at the top.
• Opening has two valves, or “trapdoors,” that open and close for the barnacle to feed.
• Vary in size from less than half an inch to 1 inch in diameter.

What species of barnacles live in the Bay?

Four species of barnacles can be found in the Bay:

• The bay barnacle, Balanus improvisus.
• The white barnacle, Balanus subalbidus.
• The ivory barnacle, Balanus eburneus.
• The little gray barnacle, Chthamalus fragilis.

Where do barnacles live?

Barnacles are found from the mouth of the Bay to nearly fresh water. They congregate on rocks, jetties, pilings, grasses, boat bottoms and other firm surfaces, mostly in intertidal to subtidal areas.

What do barnacles eat?

Barnacles feed while submerged under water. Their "trapdoors" rhythmically open and close, causing several feathery appendages to emerge from inside the barnacle and sweep in tiny particles of plankton and detritus.

How do barnacles reproduce?

Barnacles spawn in mid- to late spring in the Bay region.

• Each barnacle has both male and female organs, but its eggs must be cross-fertilized by another barnacle. A sperm tube extends from one barnacle into a neighboring barnacle to fertilize its eggs.
• Fertilized eggs remain inside the barnacle until they hatch. Tiny larvae are then released into the water.
• Larvae go through two stages that last a few days each. The second-stage larvae search for a suitable place to attach, usually among adult barnacles of the same species.
• Larvae attach themselves with a cement-like substance secreted from special glands. They soon develop shell plates that eventually cover their body.

Other facts about barnacles:

• Though barnacles look like empty mollusk shells, they are actually crustaceans like crabs and shrimp.
• Barnacle larvae are an important food source for young fish in the spring. Though millions of larvae might be released into the water, relatively few will settle and develop into adults.
• Flatworms are major predators of barnacles in the Bay. Barnacles are also 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 as blue crabs and other crustaceans molt.