Barnacles are crustaceans, related to crabs and lobsters, that attach themselves permanently to hard surfaces in marine environments. These sessile organisms are filter feeders, using feathery appendages called cirri to capture plankton and detritus from the water. They are common in shallow and tidal waters, often found on rocks, ship hulls, and even marine animals like whales. Barnacles play a role in marine ecosystems by modifying their environment and serving as a food source.
Marine Predators of Barnacles
Barnacles, despite their hard shells, serve as a food source for various marine animals. This includes certain species of sea snails, particularly whelks, which often target barnacles where they are abundant.
Starfish, also known as sea stars, are another significant predator. Species like the Ochre Sea Star (Pisaster ochraceus) regularly include barnacles in their diet. Fish also prey on barnacles, with species like Sheepshead fish (Archosargus probatocephalus) being notable consumers adapted to feed on hard-shelled invertebrates. Crabs also opportunistically consume barnacles, especially smaller or weakened individuals.
Methods of Predation
Predators employ distinct methods to access the soft body of barnacles within their protective shells. Whelks, such as the dog whelk (Nucella lapillus), use a specialized organ called a radula. This tongue-like structure, covered in tiny teeth, allows the snail to drill a hole through the barnacle’s shell. Once a hole is created, the whelk injects enzymes to digest the barnacle’s tissues, then sucks out the liquefied contents. This drilling process can take several days.
Starfish use a different approach, leveraging their tube feet to exert pressure on the barnacle’s shell plates. They grip the barnacle’s shell and slowly pry open the plates, creating a small gap. Once an opening is made, the starfish can evert its stomach into the barnacle’s shell. Digestive enzymes are then released externally, breaking down the barnacle’s soft tissues before the digested material is absorbed. Fish, like the Sheepshead, possess strong jaws and human-like teeth, including incisors and molars. These adaptations allow them to effectively crush the hard shells of barnacles, accessing the animal inside. Some fish also have a pharyngeal plate in their throat to further grind the ingested barnacles.
Barnacle Defenses
Barnacles have developed several protective features to deter predators and survive harsh marine conditions. Their primary defense is a hard, multi-plate shell made of calcium carbonate, which encases their soft bodies.
Barnacles also possess movable opercular plates, which function like a door at the top of their shell. When not feeding or sensing a threat, these plates can be tightly closed, sealing the barnacle within its armored home. This sealing mechanism protects against predators and helps conserve moisture during low tide, preventing desiccation. Barnacles also produce a powerful, fast-curing cement, anchoring them firmly to surfaces and making dislodgement difficult. Their tendency to grow in dense clusters can also make it more challenging for individual barnacles to be targeted by predators.