Filter feeder

Filter feeders are aquatic animals that feed 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, are 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.

Feeding mechanism

Filter feeding is a feeding mechanism used by aquatic animals to gather particles of food from the water around them, by having the water pass over or through a specialized filter that traps solids. The first mechanism proposed was sieving, by J. Alder and A. Hancock in 1851. The sieve theory implies that only particles as big as the mesh of the sieve can be trapped. In 1905, H. Wallengren proposed an alternative theory, that sticky limbs of the filters of animals such as mussels could collide with and trap particles smaller than the mesh size.