Barnacle feeding is not very complex or diverse in terms of strategies for acquiring food. Some species of barnacles are actually parasites and live off the bloods of others. They, however, do not have calcium carbonate plates or feeding structures called cirri. The cirri are feathery-like and move in a way that draws water into the shell allowing the barnacle to feed (Tschanz 2012).  Chthamalus fragilis, like most other barnacles, feeds by filter feeding. When the tides reach and encompass the barnacle, it opens the two plates covering its aperture opening (main opening at the top). Once those are open, the cirri, also known as the thoracic appendages, stretch into the water (EOL 2010). It tends to live in areas with stronger currents or live on motile animals, so the maximum amount of prey can pass over its thoracic appendages. The main source of nutrition for C. fragilis is plankton, but they can also eat algae or bacteria if necessary. During the winter it does not feed. Instead, it relies on food reserves (A-Z Animals 2013).

            Cirral activity while feeding can be based on a variety of factors including: size, age, and temperature. Rhythmic cirral beating is directly proportional to temperature and inversely proportional to age and size (Southward and Anderson n.d.). In other words, as size and age increase then cirral beating decreases. As temperature increases, so does cirral beating. This is mostly because when the water temperatures are warm, Chthamalus fragilis is more active than when the water temperatures are cold. The faster the rhythmic beating, the more plankton and other microorganisms barnacles can capture. However, this does take more energy. The cirri of C. fragilis are more active and upright while feeding than other species of barnacles; whose cirri have a primitive cup-shaped structure. This difference gives them a slight advantage in filtration (Southward and Anderson n.d.).

Another example of organisms that filter feed are the sponges. If you would like to learn about sponges, click on the link!



Southward, A. J. and D.T. Anderson. N.d. Cirral activity of barnacles. Barnacle Biology 5: 135-136.         

EOL 2010. <URL:>. Accessed 21 March 2014.

A-Z Animals 2013. <URL:>. Accessed 21 March 2014.

Tschanz, G. 2012. Pollicipies polymerus. BioWeb <URL:>. Accessed 21 March 2014.

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