Barnacles and Mussels

At the Edmonds dock, barnacles (Chthamalus dalli or Balanus glandula) and mussels (Mytilus trossulus or Mytilus californianus) coat pilings and other surfaces near the water surface. Barnacles are small relatives of crabs and shrimp. They have cone-shaped shells and live attached to hard surfaces, like pilings and docks. A barnacle feeds by extending six pairs of feather-like feeding appendages (called cirri), and "sifting" or combing the water for plankton and other material to eat. By looking carefully, we could see the barnacles feeding.

Mussels are bivalves, which means they have two hinged shells. Mussels attach themselves firmly to rocks and pilings with strong threads, called byssuses; although they can detach and move about using their "foot." Mussels feed by sucking water in through an intake tube (siphon), screening out microscopic food particles (plankton) with their gills, and ejecting the water through a second discharge siphon. This type of feeding is known as "filter feeding."

In an oil spill, barnacles and mussels can be coated with oil, or affected by oil that is dispersed, either naturally or by the application of dispersants. (Dispersants are chemicals that move the oil into the water column, so that much less stays at the surface, where it could affect beaches and tideflats. To learn more about dispersants, check our Dispersants Guided Tour. Our research shows that mussels are tolerant of oil exposure. Although they can be "tainted" and unfit for eating for some time, once they are again in clean water, they are able to recover by gradually clearing ("depurating") the oil from their tissues.

Few studies have been done on the effects of oil on barnacles, so we don't know how barnacles tolerate exposure to oil. (How could you do an experiment to find out how barnacles handle oil?)

(08.09.04, Edmonds, Washington)