Barnacles, commonly seen clinging to rocks and ship hulls, are fascinating marine crustaceans. Unlike mobile relatives like crabs and lobsters, adult barnacles adopt a sessile lifestyle, permanently attaching themselves to various surfaces in the ocean. This stationary existence necessitates a specialized approach to obtaining nutrition, as they cannot actively pursue prey. Barnacles filter their meals directly from the surrounding water.
Main Food Sources
Barnacles feed on microscopic organisms and particles suspended in the ocean. Their diet largely consists of plankton, including both phytoplankton and zooplankton.
Phytoplankton are tiny marine plants that form the base of many aquatic food webs. Zooplankton are minute, free-floating animals, with copepods being an important part of a barnacle’s diet. Barnacles also ingest detritus, which is organic matter from decaying plant and animal material. This omnivorous strategy allows them to use various available nutrients.
How Barnacles Capture Food
Barnacles capture their food using specialized, feathery appendages called cirri. Each barnacle has six pairs of these thoracic limbs, which they extend rhythmically from their shell into the water. The cirri act like a fine net or sieve, sweeping through the water to trap tiny food particles.
As the cirri extend and retract, they create a current that draws water and suspended food into the barnacle’s feeding zone. Once food particles are caught, the cirri withdraw, moving the captured meal toward the barnacle’s mouth for consumption. Different species use varied cirral movements, such as a constant sweeping motion or a pumping beat, to filter water.
Where Barnacles Find Food
Barnacles attach to a wide array of surfaces, including rocks, pier pilings, buoys, and the shells of other marine animals like whales. Their habitats range from the intertidal zone, which is exposed during low tide, to the perpetually submerged subtidal zones. In intertidal areas, barnacles close their protective plates when the tide recedes to prevent desiccation and open them when submerged to feed.
Food availability is greatly influenced by water currents and tidal movements, which continuously bring new particles to their sessile location. Areas with stronger water flow tend to deliver more suspended particles, supporting higher feeding rates and growth. Some barnacle species even show increased activity at night, correlating with the vertical migration of zooplankton towards the water’s surface.