Text Size: A  A  A

Barnacles

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

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

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

Appearance:

  • Six overlapping grayish or whitish shell plates
  • Flat base
  • Opening at the top has two valves that open and close like “trap doors”
  • Vary in size from less than half an inch to 1 inch in diameter

Habitat:

  • Live on rocks, reefs, jetties, pilings, grasses, boat hulls and other hard surfaces

Range:

  • Found throughout the Chesapeake Bay, from salty waters to nearly fresh water
  • The bay and white barnacles are more common in the northern half of the Bay, while the ivory and little gray barnacles are mostly found in the lower Bay

Feeding:

  • 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:

  • Spawn 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

Other Facts:

  • Although barnacles look like empty mollusk shells, they are actually crustaceans that are related to crabs and shrimp
  • Sensitive to very cold or dry weather
  • 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:

  • Life in the Chesapeake Bay by Alice Jane Lippson and Robert L. Lippson
  • Chesapeake Bay: Nature of the Estuary, A Field Guide by Christopher P. White
  • Balanus eburneus – Smithsonian Marine Station at Fort Pierce

410 Severn Avenue / Suite 112
Annapolis, Maryland 21403
Tel: (800) YOUR-BAY / Fax: (410) 267-5777
Directions to the Bay Program Office
Terms of Use | Privacy Policy
©2012 Chesapeake Bay Program | All Rights Reserved