No one is quite sure how the barnacle accomplishes this home renovation, but there is probably a chemical secretion that dissolves the inner layers while new material is added to the outside. Most barnacles are hermaphrodites, meaning they have both male and female sex organs. But to create baby barnacles, they must be fertilized by a neighbor. A retractable tube containing sperm can reach outside the shell as far as several inches to fertilize a nearby barnacle. Courtesy of Bullfrog Films and the National Film Board of Canada.
Newborn barnacles emerge from their parent's shells as one-eyed larvae.
These larvae settle to the bottom, and begin feeling around for a new home, beginning the cycle all over again. Barnacles feed on plankton they sweep from the water with their fan-like feet. The blue mussel is a competitor for space, possibly outgrowing and smothering barnacles. Excessive growth of the algae rockweed can also overpower a colony of barnacles.