Deep Ocean Life

The animals that are permanent inhabitants of this neighbourhood are carnivorous, suspension, or detritus feeders, and most of them depend on the second hand energy captured from the sun by the photosynthetic activity of their microscopic algae neighbours in the upper, lighted regions. They are adapted to catch marine snow (falling particles of dead animals and plants that live in surface waters).

To survive in the dark zone, creatures have had to develop senses other than sight as well as a few astonishing tricks. More than two thirds of the species living in this region produce bioluminescence (the emission of visible light).

Deep-sea angler fish flash in the dark; the light is produced by bacteria living permanently in their lours. The function of this flashing is to attract either prey or potential partners. Many animals are dark red; no red light penetrates this deep so these animals are virtually transparent.

Much of the deep ocean floor consists of immense plains of soft mud, covered with holes and mounds made by buried worms and other sea animals. There are also networks of tracks and trails left by the millions of echinoderms (sea cucumbers, sea urchins and brittle stars) marching along the seabed vacuuming the surface for food particles.

The animals that live on the ocean floor compose the benthic fauna

Ocean floor dwellers may live on the surface (epifauna) or beneath the surface (infauna) and usually reflect the character of the substratum; whether it’s a hard bottom of coral and rock, or a soft bottom of sand and mud. Many animals are adapted for life in the spaces between the grains of sand and compose the interstitial fauna. Numerous marine animals live on sand or mud flats, usually buried but with burrow openings.

Galatheid crabs are common burrow-dwellers on the continental slope.

The abundance of marine life in the ocean floor is directly related to the supply of plankton reaching the area and this depends on different factors such as the depth of water through which the material must travel, the proximity of additional sources of detritus and the level of water movement near the sea bed, bringing about the renewal of suspended supplies.

These are some of the physical and chemical conditions at the bottom of the sea so you can get an idea of how and why benthic organisms have adapted as they have:


around –4ºC


(effect on gravity) about 830 times that of air.

(resistance to movement)

about 60 times that of air.

Ability to transmit sound:

4 times faster than air - important for orientation, finding food and to avoid predators.

Electrical conductivity:

a million times greater than air - important for communication.

Light absorption:

little light penetrates beyond 200 – 400 m - important for photosynthesis.

Find out more about the marine environment:

The marine environment
Food webs
Deep ocean life
Hydrothermal vents

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February 2007