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Abottom feeder is an aquatic animal that feeds on or near the bottom of a body of water.[1] Biologists often use the termsbenthos—particularly for invertebrates such asshellfish,crabs,crayfish,sea anemones,starfish,snails,bristleworms andsea cucumbers—andbenthivore orbenthivorous, for fish and invertebrates that feed on material from the bottom.[2] However the termbenthos includes all aquatic life that lives on or near the bottom, which means it also includes non-animals, such as plants and algae.[3] Biologists also use specific terms that refer to bottom feeding fish, such asdemersal fish,groundfish,benthic fish andbenthopelagic fish.[4] Examples of bottom feeding fish species groups areflatfish (halibut,flounder,plaice,sole),eels,cod,haddock,bass,carp,grouper,bream (snapper) and some species ofcatfish andsharks.[4]
Some bottom feeders aredetritivores,[3] taking advantage oforganic materials that sink down through bodies of water to the bottom.[1] In ocean environments, this downward drift of detritus is known asmarine snow.[5] Bottom feeders may gatherdetritus manually, as somecrab species do; or filter microparticles out of the water usingsuspension feeding.[3] Thisbiotic decomposition and recycling of organic matter is critical for the health of many aquatic environments as it helps maintain variousbiogeochemical cycles.[3] In 2014, it was reported thatdeep sea bottom feeders absorbcarbon dioxide by eating creatures such asjellyfish andcephalopods, allowing thegreenhouse gas to be retained at the sea floor rather than be released back into the atmosphere.[6]
Other bottom feeders graze on livingaquatic plants andmacroalgae, as is the case in somesea urchin species.[7]
Lastly, some bottom feeders arecarnivorous and specialize in either hunting other benthic animals, orscavenging from bodies killed by other predators.[8] Some bottom feeding predators use the floor terrain as cover toambush their prey.[4] One common method is the animal using body movements to stir up sand and conceal itself with sediment, a tactic used by many species offlatfish;[4] or simply hide inside burrows or around other existing covers, such as many species ofoctopus andmantis shrimps, before suddenly emerging from cover to catch unsuspecting prey with fast strikes.[4] Others burrow deep into the floor and hunt with most of the body remaining buried, as in the case of oceanicbobbit worms.[9] In darker deep waters, some bottom predators usesaggressive mimicry andbioluminescence to visually lure and ambush prey, as in the case ofanglerfish.
In fish, most bottom feeders exhibit a flat ventral region so as to more easily rest their body on the substrate.[4] The exception may be the flatfish, which are laterally depressed but lie on their sides.[4] Also, many exhibit what is termed an "inferior" mouth, which means that the mouth is pointed downwards; this is beneficial as their food is often going to be below them in the substrate.[4] Those bottom feeders with upward-pointing mouths, such asstargazers, tend to seize swimming prey.[10] Some flatfish such ashalibut actually have a "migrating" eye that moves to the upward-facing side of the fish as it ages.[4]
In theaquarium, bottom feeders are popular as it is perceived that they will clean the algae that grows in the tank. Generally, they are only useful for consuming the extra (fresh) food left by overfed or clumsy livestock; the added biomass of additional organisms means that the aquarium will likely be more dirty.[11] Some specialized bottom feeders are more specifically sold as "algae eaters" to increase the amount of free oxygen and aesthetic appeal of a tank.[12]
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