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Benthos are the organisms which live on, in, or near the seabed, also known as the benthic zone.^[1] They live 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 meters 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 for "depths of the sea".^[1] 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.^[2]

The main food sources for benthos are plankton 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 pelecypods, dominate hard, sandy bottoms. Deposit eaters, such as polychaetes, populate softer bottoms. Fish, sea stars, snails, cephalopods, and crustaceans are important predators and scavengers.

Benthic organisms, such as sea stars, oysters, clams, sea cucumbers, brittle stars and sea anemones, play an important role as a food source for fish and humans.

Macrobenthos are the larger, more visible, benthos 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.

• 
  Seagrass growing off the coast.
• 
  Echinoderms.
• 
  A sea squirt being used as a substrate for a nudibranch's egg. spiral.
• 
  Microphotograph of typical macrobenthic animals.

Meiobenthos are tiny benthos that are less than 1 mm but greater than 32 µm in size. Some examples are nematodes, foraminiferans, water bears, gastrotriches and smaller crustaceans such as copepods and ostracodes.

• 
  Live foraminifera Ammonia tepida (Rotaliida)
• 
  water bear Hypsibius dujardini
• 
  Gastrotrich.
• 
  Copepod

Microbenthos are microscopic benthos that are less than 32 µm in size. Some examples are bacteria, diatoms, ciliates, amoeba, flagellates

• 
  Marine diatoms
• 
  Ciliate stentor roeseli
• Amoeba
  Amoeba
• 
  Flagellate

Zoobenthos are animals belonging to the benthos.

Phytobenthos are plants belonging to the benthos.

Epibenthos live on top of the sediment

Hyperbenthos live just above the sediment

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• Aphotic zone
• Bottom feeder
• Deep sea
• Intertidal ecology

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• Littoral
• Neritic zone
• Pelagic zone
• Photic zone

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• Profundal zone
• Sediment Profile Imagery (SPI)
• Stream bed

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Contrast the terms plankton (the organisms that float or drift within the water), nekton (the organisms that swim (powerfully) in the water), and neuston (the organisms that float on the water).

• 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.

• Benthos

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