What are marine benthos?

The marine benthos include the set of organisms that live in, on, or near the seafloorthat is, those who live in the benthic zone. Similarly, benthos also appear in any other aquatic ecosystem, not only in the sea.

Benthic communities therefore encompass a variety of habitats as different as sedimentary environments, tidal pools along coastlines, or the depths of ocean abysses.

And if the conditions of the benthos are very different, equally different are the organisms that live in it. We can find crawling organisms, burrowers, others that remain anchored to the bottom substrate or even swimming organisms but remain close to the bottom.

In the benthos exposed to light there are photosynthetic organisms, especially algae, but as the depth decreases, the light becomes scarcer until it reaches absolute darkness.

This makes the algae, together with the organic matter dragged from the mainland, the main primary source of food in the benthic food chain. In the deepest benthos, the food source is decomposing organic matter that falls from higher areas, which is why detritivorous and decomposing organisms abound in the benthos.

In addition to the depth, it also affects the temperature, the salinity of the water and the type of substrate present (rock, sand, etc.). For example, in coastal waters where light reaches the bottom, diatoms and photosynthetic algae can proliferate; filter feeders, such as sponges and bivalves, dominate the sandy and rocky bottoms.

Detritivorous organisms, such as polychaetes, proliferate in soft aquatic soils. Other benthos animals, such as starfish, snails, cephalopods, sea cucumbers or crustaceans, are very important in the marine food chain, being the food of numerous species of fish, and are also widely consumed by humans.

types of benthos

Benthos can be classified according to various criteria.

Benthos by size of organisms

  • macrobenthos: comprise the largest organisms that can be seen with the naked eye. Its size is usually greater than 3 mm, although there are macrobenthos as small as 0.5 mm in length. Examples: polychaete worms, bivalves, echinoderms, sea anemones, corals, crustaceans such as crabs and lobsters.
  • Meiobenthos: Meiobenthos comprise benthic organisms smaller than 1 mm but larger than 0.1 mm. Examples: nematodes, foraminifera, tardigrades, gastrotrichs, small crustaceans such as copepods or ostracods.
  • microbenthos: microscopic benthic organisms. Its size is usually less than 0.1 mm. Examples: bacteria, diatoms, amoebas, ciliophores.

Benthos by type of organisms

  • zoobenthos: benthic animals.
  • phytobenthos: benthic plants, macroalgae and photosynthetic diatoms.

benthos by location

  • endobenthos: organisms that live buried in the sediments of the seabed, generally in the upper layers of the sediment where oxygenated water arrives.
  • Epibenthos: they live on the sediment or seabed.
  • hyperbenthos: they live in the water near the seabed, for example the fish Lotella rhacina (rock cod).
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