ABSTRACT
The oceanic zone is generally defined as those waters beyond the 200 m isobath at the edge of the continental shelf extending out and encompassing the ocean basins. This contrasts with the neritic zone that extends from the shore and is the water above the continental shelf. The pelagic zone includes all open waters that are not close to the bottom and is divided into the epipelagic, mesopelagic, bathypelagic, abyssopelagic, and hadopelagic zones that are distinguished by their depth and ecology (Bone, Marshall, and Blaxter 1995). The epipelagic zone extends from the surface down to 200 m and has an abundance of light that allows for photosynthesis. Nearly all primary production in the ocean occurs here and this is where most organisms are concentrated (Pinet 2006). About 80% of the ocean’s surface is above water greater than 200 m in depth. In general, species diversity tends to decrease as one leaves the shore and the food web becomes supported by the planktonic production. Extending down from the epipelagic zone is the mesopelagic zone, or twilight zone, that reaches to a depth of 1000 m and has a little light but not enough for photosynthesis to occur. Together, the epipelagic and mesopelagic zones, where light penetrates the water, are known as the photic zone. The pelagic zone occupies about 1370 million cubic km (330 million cubic miles) and has a vertical range up to 11 km (6.8 miles). The diversity and abundance of pelagic life decrease with increasing depth. It is affected by light levels, pressure, temperature, salinity, the supply of dissolved oxygen and nutrients, and the submarine topography.
