Benthos are the organisms which live in the benthic zone, and are different from those elsewhere in the water column. Many are adapted to live on the substrate (bottom). In their habitats they can be considered as dominant creatures, but they are often a source of prey for Carcharhinidae such as the lemon shark. [2] 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 meters of water depth).
Because light does not penetrate very deep into ocean-water, the energy source for the benthic ecosystem 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. Some microorganisms use chemosynthesis to produce biomass.
Benthic organisms can be divided into two categories based on whether they make their home on the ocean floor or an inch or two into the ocean floor. Those living on the surface of the ocean floor are known as epifauna.[3] Those who live burrowed into the ocean floor are known as infauna.[4] Extremophiles like the piezophile which can survive in high pressures may also live there.
For comparison, the pelagic zone is the descriptive term for the ecological region above the benthos, including the water-column up to the surface. Depending on the water-body, the benthic zone may include areas which are only a few inches below water, such as a stream or shallow pond; at the other end of the spectrum, benthos of the deep ocean includes the bottom levels of the oceanic abyssal zone.
For information on animals that live in the deeper areas of the oceans see aphotic zone. Generally, these include life forms that tolerate cool temperatures and low oxygen levels, but this depends on the depth of the water.