Coastal Aquaculture and Mariculture

Unit 1 - Fishery Zones and Fishery resources

1.3. Divisions of Pelagic Zones
Depending on how deep the sea is, there can be up to five vertical layers in the ocean. From the top down, they are:
1.Epipelagic
It is a pelagic zone from the surface (MSL) down to around 200 m (656 ft). It is the illuminated surface zone where there is enough light for photosynthesis. Due to this, plants and animals are largely concentrated in this zone. Nearly all primary food production in the ocean occurs here.
2.Mesopelagic
It is a pelagic zone from 200 m down to around 1,000 m (3,280 ft). Although some light penetrates this deep, it is insufficient for photosynthesis. The name stems from Greek, meso meaning middle.
3.Bathypelagic
It is a pelagic zone from 1,000 m down to around 4,000 m (13,123 ft). By this depth the ocean is almost entirely dark (with only the occasional thennoluminescent organism, such as lantemfish). The name stems from Greek, baths meaning deep.
4.Abyssopelagic
It is a pelagic zone from 4,000 m down to above the ocean floor. No light whatsoever penetrates to this depth. The name is derived from the Greek, abyss, meaning bottomless.
5.Hadopelagic
It is the deep water in ocean trenches. The name is derived from the Greek, Hades, meaning underworld. Some define the hadopelagic as waters below 6,000 m (19,685 ft), whether in a trench or not.

The bathypelagic, abyssopelagic, and hadopelagic zones are very similar in character. and some marine biologists elide them into a single zone or consider the latter two to be the same. The marine environment is made into several zones as below for the administrative purposes with a view to utilize and manage the resources in a proper way.