Bathyal zone
Overview
 
The bathyal zone or bathypelagic – from Greek βαθύς (bathýs), deep – (also known as midnight zone) is that part of the pelagic zone
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...

 that extends from a depth of 1000 to 4000 metres (3300 to 13000 feet) below the ocean surface
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

. It lies between the mesopelagic
Mesopelagic
The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all...

 above, and the abyssopelagic below. The average temperature hovers at about 39°F (4°C). Although larger by volume than the euphotic zone, the bathyal zone is less densely populated.
Encyclopedia
The bathyal zone or bathypelagic – from Greek βαθύς (bathýs), deep – (also known as midnight zone) is that part of the pelagic zone
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...

 that extends from a depth of 1000 to 4000 metres (3300 to 13000 feet) below the ocean surface
Sea level
Mean sea level is a measure of the average height of the ocean's surface ; used as a standard in reckoning land elevation...

. It lies between the mesopelagic
Mesopelagic
The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all...

 above, and the abyssopelagic below. The average temperature hovers at about 39°F (4°C). Although larger by volume than the euphotic zone, the bathyal zone is less densely populated. Sunlight does not reach this zone, meaning there can be no primary production
Primary production
400px|thumb|Global oceanic and terrestrial photoautotroph abundance, from September [[1997]] to August 2000. As an estimate of autotroph biomass, it is only a rough indicator of primary production potential, and not an actual estimate of it...

. It is known as the midnight zone because of this feature. Because of the lack of light, some species do not have eyes, however those possessing eyes in this zone include the viperfish
Viperfish
A viperfish is a saltwater fish in the genus Chauliodus, with long, needle-like teeth and hinged lower jaws. They grow to lengths of 30 to 60 cm . Viperfish stay near lower depths in the daytime and shallow at night. Viperfish mainly stay in tropical and temperate waters...

 and the frill shark
Frill shark
The frilled shark is one of two extant species of shark in the family Chlamydoselachidae, with a wide but patchy distribution in the Atlantic and Pacific Oceans. This uncommon species is found over the outer continental shelf and upper continental slope, generally near the bottom though there is...

. Many forms of nekton
Nekton
Nekton refers to the aggregate of actively swimming aquatic organisms in a body of water able to move independently of water currents....

 live in the bathyal zone, such as squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...

, large whale
Whale
Whale is the common name for various marine mammals of the order Cetacea. The term whale sometimes refers to all cetaceans, but more often it excludes dolphins and porpoises, which belong to suborder Odontoceti . This suborder also includes the sperm whale, killer whale, pilot whale, and beluga...

s and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...

es, but this zone is difficult for fish to live in. Sponges, brachiopods, sea stars, and echinoids are also common in the bathyal zone. The fish in this zone have become very energy efficient, since it is especially hard to find nutrients. Many have slow metabolic rates to conserve energy. The fish here have weak muscles, soft skin and slimy bodies. Animals in the bathyal zone are not threatened by predator
Predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

s that can see them, so they do not have powerful muscles. Animals need to have the right adaptions to survive in this lethal area. There are no plants because of the lack of sunlight, not enough to for photosynthesis. In the bathyal some of the world's largest whales feed.

Except where the ocean is exceptionally deep, the bathyal zone extends to the benthic zone
Benthic zone
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean or a lake, including the sediment surface and some sub-surface layers. Organisms living in this zone are called benthos. They generally live in close relationship with the substrate bottom; many such...

 on the ocean bed of that part of the continental slope that lies between 1000 and 4000 metres deep.
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