Barnacles are crustaceans, distantly related to crabs and lobsters, known for their unique ability to permanently attach to surfaces. Though their hard shells resemble mollusks, adult barnacles are sessile filter feeders, straining food particles from water. This lifestyle, adopted after a free-swimming larval stage, allows them to inhabit diverse global environments.
Coastal and Intertidal Habitats
Barnacles are most familiar in coastal and intertidal zones, areas experiencing tidal rise and fall. Rocky shores offer abundant attachment surfaces for species like acorn barnacles (e.g., Balanus glandula and Semibalanus balanoides). They anchor firmly with a strong natural glue, withstanding powerful wave action.
In these habitats, barnacles face environmental challenges like air exposure, temperature fluctuations, and desiccation during low tide. They survive with a protective shell and an operculum, a “door” that seals tightly to prevent water loss and protect against predators. Different species occupy specific vertical zones, some tolerating more desiccation and higher shore positions. Tide pools, pilings, and docks also offer suitable attachment sites.
Deeper Ocean and Open Water Environments
Beyond the shoreline, barnacles inhabit subtidal zones and the open ocean. Subtidal barnacles live below the lowest tide mark, continuously submerged. This constant water cover means they do not face the desiccation challenges of their intertidal relatives.
In the pelagic environment, barnacles often attach to floating debris, buoys, and other drifting objects. Gooseneck barnacles (Lepas species), with their distinctive stalks, are commonly found on driftwood and marine plastic, adapting to mobile existence. Even deep-sea hydrothermal vents, with extreme temperatures and chemical conditions, host specialized barnacle species.
Barnacles on Living Hosts and Human Creations
Barnacles attach to living organisms and man-made structures, often creating complex ecological interactions. Whale barnacles, such as Coronula diadema on humpback whales, exemplify a commensal relationship: the barnacle benefits from transportation and increased food access, while the whale is generally unaffected. These barnacles position themselves on areas of consistent water flow, like a whale’s head or chin, to optimize filter-feeding.
Various barnacle species, including Chelonibia testudinaria, attach to sea turtles. While often commensal, heavy loads can increase drag for the turtle, and some species embed into the skin or shell, potentially causing discomfort or health issues. Human creations like ship hulls, submarines, and other marine infrastructure provide abundant surfaces for barnacle colonization, known as biofouling. This attachment increases drag, leading to higher fuel consumption for vessels and economic costs for the shipping industry.
Global Distribution and Influencing Factors
Barnacles are found across all major oceans, from polar regions to the tropics, adapting to diverse marine conditions. Their global distribution is shaped by environmental factors. Salinity is a primary determinant; most barnacles are exclusively marine and require specific salt concentrations, though some tolerate brackish waters.
Water temperature also plays a role, with warmer tropical and subtropical waters promoting faster growth and settlement. Wave action influences barnacle morphology and attachment strength in intertidal zones. Strong currents impact larval dispersal and adult feeding. Finally, suitable attachment substrates—natural rock, floating debris, or living hosts—are fundamental to barnacle presence. These interconnected factors create the diversity of barnacle habitats observed worldwide.