Pelagic zone
From Simple English Wikipedia, the free encyclopedia
The pelagic zone is the part of the open sea or ocean that is not near the coast or sea floor. The name comes from the Greek πέλαγος (pélagos), which might be roughly translated as "sea" but is more accurately translated as "open sea."
[edit] Sub-sections of the pelagic zone
The pelagic zone (also known as the open-ocean zone) is divided into parts, creating a number of sub-zones, based on their different ecological characteristics (which is roughly a function of depth):
- Epipelagic (from the surface down to around 200 m) - the illuminated surface zone where there is enough light for photosynthesis. Due to this, plants and animals are largely concentrated in this zone. Here one will typically find fish such as tuna and many sharks.
- Mesopelagic (from 200 m down to around 1000 m) - the twilight zone. Although some light penetrates this deep, it is insufficient for photosynthesis. The name comes from Greek μέσον, middle.
- Bathypelagic (from 1000 m down to around 4000 m) - by this depth the ocean is almost entirely dark (with only the occasional bioluminescent organism). There are no living plants, and most animals survive by consuming the snow of detritus falling from the zones above, or (like the marine hatchetfish) by preying upon others. Giant squid live at this depth, and here they are hunted by deep-diving sperm whales. From Greek βαθύς (bathys), deep.
- Abyssopelagic (from 4000 m down to above the ocean floor) - no light whatsoever penetrates to this depth, and most creatures are blind and colourless. The name comes from the Greek άβυσσος (ábyssos), abyss, and means bottomless (because in ancient times the deep ocean was believed to be bottomless).
- Hadopelagic (the deep water in ocean trenches) - the name comes from Hades, the classical Greek underworld. This zone is 90% unknown and very few species are known to live here (in the open areas). But many organisms live in hydrothermal vents in this and other zones.
The bathypelagic, abyssopelagic, and hadopelagic zones are very similar in character, and some marine biologists count them as a single zone or consider the latter two to be the one zone. Some define the hadopelagic as waters below 6000 meters, whether in a trench or not.
