What are marine benthos?

The marine benthos comprise the set of organisms that live in, on or near the seabed , that is, those that inhabit the benthic zone . Analogously, benthos also appear in any other aquatic ecosystem, not just in the sea.

Benthic communities therefore encompass a variety of habitats as different as the sedimentary environments, the tide pools that occur along the shorelines or the depths of oceanic abysses.

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

In the benthos exposed to light there are photosynthetic organisms, highlighting the algae, but as the depth decreases, the light becomes more scarce until reaching absolute darkness.


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

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 may proliferate ; filtering organisms, such as sponges and bivalves, dominate the sandy and rocky bottoms.

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


Types of benthos

Benthos can be classified according to different criteria.

Bentos 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 of only 0.5 mm in length. Examples: polychaete worms, bivalves, echinoderms, sea anemones, corals, crustaceans such as crab and lobster.
  • Meiobenthos : Meiobenthos comprise benthic organisms less than 1 mm in size but greater than 0.1 mm. Examples: nematodes, foraminifera , tardigrades, gastrotics, small crustaceans such as copepods or ostracods.
  • Microbenthos : microscopic benthic organisms. Its size is usually less than 0.1 mm. Examples: bacteria, diatoms, amoebas,  ciliophora

Bentos by type of organisms

  • Zoobentos : benthic animals.
  • Phytobenthos : benthic plants, macroalgae and photosynthetic diatoms.

Bentos by location

  • Endobentos : organisms that live buried in the sediments of the seabed, usually in the upper layers of the sediment where oxygenated water arrives.
  • Epi Bentos : live on the sediment or seabed.
  • Hyperbenthos : live in the water near the seabed, for example the fish Lotella rhacina(rock cod).

What is anoxygenic photosynthesis?

Pelagic and benthic marine organisms