How Barnacles Live and Eat
Barnacles are marine crustaceans, distantly related to crabs and lobsters. Unlike their mobile relatives, adult barnacles are sessile, fixed permanently to a surface. They are recognized by their hard, calcified shells, resembling small volcanoes or acorn-shaped structures, often found encrusting rocks, ship hulls, or whales worldwide. This protective outer shell allows them to survive in harsh intertidal zones.
Adult barnacles attach to a substrate using a biological adhesive produced by specialized cement glands at the base of their first antennae. This natural “superglue” is a protein-based substance that cures underwater, forming a strong bond to various surfaces, including rock, wood, metal, and other organisms. This adhesion helps them resist wave action and currents.
Once anchored, barnacles feed by extending feathery, net-like appendages called cirri through an opening in their shell. These cirri are modified thoracic legs, adapted for filter feeding. By rhythmically sweeping these cirri through the water, barnacles capture plankton, detritus, and other small organic particles. This mechanism allows them to extract nutrients from their environment.
The Barnacle Life Cycle
The barnacle life cycle begins with microscopic, free-swimming larval stages. The first larval stage is the nauplius, which hatches from eggs and drifts in ocean currents as zooplankton. These larvae focus on feeding and growth. The nauplius undergoes several molts, increasing in size with each stage.
After a series of naupliar stages, the larva transforms into a cyprid, a non-feeding, specialized larval stage. The cyprid larva is the dispersal and settlement stage, equipped with sensory organs to explore potential attachment sites. It uses its modified antennules to “walk” along surfaces, assessing suitability based on factors like texture, presence of other barnacles, and biofilm. This exploration ensures the larva selects an optimal location for its adult life.
Once a suitable surface is identified, the cyprid larva attaches headfirst using a temporary adhesive secreted from its antennules. It then undergoes metamorphosis, transforming into the adult form. During this process, the larval body reorganizes, developing the characteristic calcified plates and internal structures of the adult barnacle. Most barnacles are hermaphroditic, possessing both male and female reproductive organs, and typically engage in cross-fertilization with nearby individuals to ensure genetic diversity.
Barnacles in Their Environment
Barnacles play a role in marine ecosystems, primarily through their filter-feeding activity. By constantly filtering water to capture plankton and organic particles, they contribute to water clarification in coastal areas. This continuous removal of suspended matter can influence water quality and nutrient cycling. Their presence can also create microhabitats for other small marine organisms.
As filter feeders, barnacles also serve as a food source for various marine animals, including certain fish, snails, and sea stars. These predators graze on barnacle populations, integrating them into the broader marine food web. The hard shells of barnacles provide a protective covering, making them a relatively tough meal for many consumers.
Despite their ecological contributions, barnacles are known as “fouling organisms” due to their tendency to attach to artificial marine structures. They commonly colonize ship hulls, increasing drag and consequently fuel consumption for maritime vessels. Barnacle growth on underwater infrastructure like piers, buoys, and aquaculture equipment can necessitate costly maintenance and cleaning. This impact highlights their presence in both natural and human-modified marine environments.