Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone. This community lives in or near marine 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 upper parts of the water column. The pressure difference can be very significant (approximately one atmosphere for each 10 metres of water depth).
Because light does not penetrate very deep ocean-water, the energy source for deep benthic ecosystems is often organic matter from higher up in the water column which 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 comes from the Greek noun βένθος "depths of the sea". Benthos is also used in freshwater biology to refer to organisms at the bottom of freshwater bodies of water, such as lakes, rivers, and streams.
Food sources 
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, sea stars, snails, cephalopods, and crustaceans are important predators and scavengers.
By size 
|Macrobenthos comprises the larger, more visible, benthic organisms that are greater than 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.|
|Meiobenthos comprises tiny benthic organisms that are less than 1 mm but greater than 0.1 mm in size. Some examples are nematodes, foraminiferans, water bears, gastrotriches and smaller crustaceans such as copepods and ostracodes.|
|Microbenthos comprises microscopic benthic organisms that are less than 0.1 mm in size. Some examples are bacteria, diatoms, ciliates, amoeba, flagellates.|
By type 
Zoobenthos comprises the animals belonging to the benthos.
By location 
Epibenthos lives on top of the sediments, i.e., like a sea cucumber or a sea snail crawling about.
Hyperbenthos lives just above the sediment, i.e., a rock cod.
See also 
- Benthos from the Census of Antarctic Marine Life website
- North American Benthological Society website
- Benthos. (2008) Encyclopædia Britannica. (Retrieved May 15, 2008, from Encyclopædia Britannica Online.)
- Ryan, Paddy (2007) Benthic communities Te Ara - the Encyclopædia of New Zealand, updated 21 September 2007.
- Yip, Maricela and Madl, Pierre (1999) Benthos University of Salzburg.