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).^[2]

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 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][3] 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.^[4]

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

They are easily visible to the naked eye with the lower range of body size at 0.5 mm but usually larger than 3 mm. In the coastal water ecosystem, they include several species of organisms, which cut across different taxa including Porifera, Annelids, Coelenterates, Mollusks, Crustaceans, Arthropods and etc.^[2]

Seagrass growing off the coast

Echinoderms

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

Live foraminifera Ammonia tepida (Rotaliida)

Water bear Hypsibius dujardini

Gastrotrich

Copepod

Microbenthos

Marine diatoms

Ciliate stentor roeseli

Flagellate

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, e.g., a sea pen or a sand dollar.

Epibenthos

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

Hyperbenthos

Hyperbenthos lives just above the sediment, e.g., 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 2 Benthos from the Census of Antarctic Marine Life website
2. 1 2 Walag, Angelo Mark (2016). "Physico-chemical Parameters and Macrobenthic Invertebrates of the Intertidal Zone of Gusa, Cagayan de Oro City, Philippines" (PDF). Advances in Environmental Sciences - International Journal of the Bioflux Society. Retrieved October 27, 2015. 
3. ↑ βένθος. Liddell, Henry George; Scott, Robert; A Greek–English Lexicon at the Perseus Project.
4. ↑ North American Benthological Society website

References

• 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.

External links

• Benthos

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