Nomination for a World Heritage Site 2009 - Phoenix Islands ...

This layer is the domain of many fish species such as tuna, many sharks, dolphin fish, and
jellyfish.
Mesopelagic zone reaches from 200 meter to about 1000 meters depth. Although some light
penetrates this deep, it is insufficient for photosynthesis. At about 500 m the water becomes
depleted of oxygen. Still, an abundance of life copes with more efficient gills or minimal
movement. Animals such as swordfish, squid, wolffish, a few species of cuttlefish, and other
semi-deep-sea fauna can be found in this zone.
Below 1000 meters depth starts the deep sea area where very little or no light penetrates.
Most of its organisms rely for subsistence on falling organic matter (known as ‘marine
snow’) and carcasses derived from the productive zone above. For this reason it was assumed
life would be sparse in these great depths, but virtually every probe has revealed that, on the
contrary, life is abundant in the deep sea. To date the deep sea represents one of the least
explored areas on Earth, it is less known than the moon. The deep sea has been divided into
bathypelagic, abyssopelagic and hadopelagic zones.
Bathypelagic zone extends from a depth of 1000 to 4000 meters below the ocean surface. The
average temperature is about 4 ºC. Although larger by volume than the above euphotic zone,
the bathyal zone is less densely populated. Sunlight does not reach this zone, meaning there
can be no primary production. Many forms of nekton live in the bathyal zone, such as squid,
viperfish, deepwater sharks, large whales, and octopuses. Sponges, brachiopods, sea stars,
and echinoids are also common in the bathyal zone. The fish in this zone have become very
energy efficient. Many have slow metabolic rates, to conserve energy. By volume the
bathypelagic zone is the most widespread habit in PIPA.
Abyssopelagic zone extends from 4,000 to 6,000 meters and contains the very deep benthic
communities near the bottom of oceans. This zone remains in perpetual darkness and never
receives daylight. Species found in this zone include the Black swallower, tripod fish, deepsea
anglerfish and the giant squid which are able to withstand the immense pressures of the
ocean depths, up to 76 megapascals (11,000 psi – pounds per square inch). The deep trenches
or fissures that plunge down thousands of metres below the ocean floor are almost
unexplored. These regions are also characterized by continuous cold and lack of nutrients.
The abyssal zone has temperatures around 2 to 3 ºC.
Hadopelagic zone is the delineation for the deepest trenches in the ocean. This zone is found
from a depth of around 6,000 meters to the bottom of the ocean. The pressure can reach over
1,100 standard atmospheres (110 MPa /16,000 psi). The most common fauna include
jellyfish, viperfish, tube worms, clams, and the deep sea angler fish.
The deep sea species have a number of ways to adapt to these extreme conditions. For
example the midwater fish are small, usually under 25cm; they have slow metabolisms and
unspecialized diets, preferring to sit and wait for food rather than waste energy searching for
it. Because of the sparse distribution and lack of light, finding a partner with which to breed
is difficult, and many organisms are hermaphroditic.
It is noteworthy that globally the ocean floor between 4,000 m and 6,000 m is the single most
extensive natural habitat, representing about 60% of the surface of the planet.
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