The buoy barnacle (Dosima fascicularis) is a species of goose barnacle known for its unique characteristic of hanging downwards from a buoyant appendage which drifts at the water surface and is carried along by ocean currents. It is regarded as "the most specialized pleustonic goose barnacle" as most other barnacle species are sessile filter feeders that remain fixed onto other firm surfaces. Formerly placed in the genus Lepas, the buoy barnacle is now generally placed in the genus Dosima, which is distinguished from Lepas by the form of the carina, and by the exceptional thinness and brittleness of its exoskeleton.
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Buoy barnacle in the context of Suspension feeding
Filter feeders are aquatic animals that acquire nutrients by feeding on organic matter, food particles or smaller organisms (bacteria, microalgae and zooplanktons) suspended in water, typically by having the water pass over or through a specialized filtering organ that sieves out and/or traps solids. Filter feeders can play an important role in condensing biomass and removing excess nutrients (such as nitrogen and phosphate) from the local waterbody, and are therefore considered water-cleaning ecosystem engineers. They are also important in bioaccumulation and, as a result, as indicator organisms.
Filter feeders can be sessile, planktonic, nektonic or even neustonic (in the case of the buoy barnacle) depending on the species and the niches they have evolved to occupy. Extant species that rely on such method of feeding encompass numerous phyla, including poriferans (sponges), cnidarians (jellyfish, sea pens and corals), arthropods (krill, mysids and barnacles), molluscs (bivalves, such as clams, scallops and oysters), echinoderms (sea lilies) and chordates (lancelets, sea squirts and salps, as well as many marine vertebrates such as most species of forage fish, American paddlefish, silver and bighead carps, baleen whales, manta ray and three species of sharks—the whale shark, basking shark and megamouth shark). Some water birds such as flamingos and certain duck species, though predominantly terrestrial, are also filter feeders when foraging.