Benthos

Seaweed and two chitons in a tide pool

Benthos is the community of organisms which live on, in, or near the seabed, also known as the benthic zone.[1] 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 "depth of the sea".[1][2] 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.[3]

Food sources

Effect of eutrophication on marine benthic life

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.

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, such as the California sheephead, and humans.

By size

Macrobenthos

Main article: Macrobenthos
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.
Seagrass growing off the coast
A sea squirt being used as a substrate for a nudibranch's spiral egg
Microphotograph of typical macrobenthic animals, (from top to bottom) including amphipods, a polychaete worm, a snail, and a chironomous midge larvae

Meiobenthos

Main article: Meiobenthos
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

Microbenthos comprises microscopic benthic organisms that are less than 0.1 mm in size. Some examples are bacteria, diatoms, ciliates, amoeba, flagellates.

By type

"A variety of marine worms": plate from Das Meer by M. J. Schleiden (1804–1881).

Zoobenthos

Zoobenthos comprises the animals belonging to the benthos.

Phytobenthos

Phytobenthos comprises the plants belonging to the benthos, mainly benthic diatoms and macroalgae (seaweed).

By location

Endobenthos

Endobenthos lives buried, or burrowing in the sediment, often in the oxygenated top layer, i.e., a sea pen or a sand dollar.

Epibenthos

Epibenthos lives on top of the sediments, i.e., like a sea cucumber or a sea snail crawling about.

Hyperbenthos

Hyperbenthos lives just above the sediment, i.e., a rock cod.

See also

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).

Notes

  1. ↑ 1.0 1.1 Benthos from the Census of Antarctic Marine Life website
  2. ↑ βένθος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
  3. ↑ North American Benthological Society website

References

External links