Benthos, also known as benthon, from Greek benthos 'depth of the sea', is the community of organisms that live on, in, or near the seabed, river, lake, or stream bottom, also known as the benthic zone. This community lives in or near marine or freshwater sedimentary environments, from tidal pools along the foreshore, out to the continental shelf, and then down to the abyssal depths.
Many organisms adapted to deep-water pressure cannot survive in the upperparts of the water column. The pressure difference can be very significant (approximately one atmosphere for each 10 metres of water depth).
Because light is absorbed before it can reach deep ocean-water, the energy source for deep benthic ecosystems is often organic matter from higher up in the water column that drifts down to the depths. This dead and decaying matter sustains the benthic food chain; most organisms in the benthic zone are scavengers or detritivores.
The term benthos, coined by Haeckel in 1891, comes from the Greek noun βένθος 'depth of the sea'. Benthos is used in freshwater biology to refer to organisms at the bottom of freshwater bodies of water, such as lakes, rivers, and streams. There is also a redundant synonym, benthon.
The main food sources for the benthos are algae and organic runoff from land. The depth of water, temperature and salinity, and type of local substrate all affect what benthos is present. In coastal waters and other places where light reaches the bottom, benthic photosynthesizing diatoms can proliferate. Filter feeders, such as sponges and bivalves, dominate hard, sandy bottoms. Deposit feeders, such as polychaetes, populate softer bottoms. Fish, such as dragonets, as well as sea stars, snails, cephalopods, and crustaceans are important predators and scavengers.
Macrobenthos, prefix from Greek makrós 'long', comprises the larger, visible to the naked eye, benthic organisms greater than about 1 mm in size. Some examples are polychaete worms, bivalves, echinoderms, sea anemones, corals, sponges, sea squirts, turbellarians and larger crustaceans such as crabs, lobsters and cumaceans.
- Sea squirts
Meiobenthos, prefix from Greek omeíkhō 'halfway, middle', comprises tiny benthic organisms that are less than about 1 mm but greater than about 0.1 mm in size. Some examples are nematodes, foraminiferans, tardigrades, gastrotriches and smaller crustaceans such as copepods and ostracodes.
- Tardigrade (water bear)
Zoobenthos, prefix from the Greek zôion 'animal', comprises the animals belonging to the benthos.
Endobenthos, prefix from the Greek éndon 'inner, internal', lives buried, or burrowing in the sediment, often in the oxygenated top layer, e.g., a sea pen or a sand dollar.
Epibenthos, prefix from the Greek epí 'on top of', lives on top of the sediments, e.g., like a sea cucumber or a sea snail crawling about. Unlike other epiphytes.
Hyperbenthos, prefix from the Greek hupér 'over', lives just above the sediment, e.g., a rock cod.
- Benthos from the Census of Antarctic Marine Life website
- US Department of Commerce, National Oceanic and Atmospheric Administration. "How does pressure change with ocean depth?". oceanservice.noaa.gov.
- Haeckel, E. 1891. Plankton-Studien. Jenaische Zeitschrift für Naturwissenschaft 25 / (Neue Folge) 18: 232-336. BHL.
- βένθος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
- "North American Benthological Society website". Archived from the original on 2008-07-05. Retrieved 2008-08-16.
- Nehring, S. & Albrecht, U. (1997). Benthos und das redundante Benthon: Neologismen in der deutschsprachigen Limnologie. Lauterbornia 31: 17-30, .