What are the various zones of an ocean?« Back to Questions List

We all know that ocean contains a wide variety of life forms. It is basically divided into two areas – ocean floor (benthic zone) and ocean waters (pelagic zone). The pelagic zone could further be classified into three zones – sunlit zone, twilight zone and midnight zone.



Photomicrograph of typical benthic animals,(from top to bottom) including amphipods, a polychaete worm, a snail, and a chironomous midge larvae


The uppermost layer of the ocean that receives sunlight throughout the day is the sunlit zone or euphotic zone. The water in this zone is slightly warm allowing wide variety of plants to survive. Almost 90% of all marine life forms like algae, seed weeds, phytoplankton, flowering plants, sharks, tuna, mackerel, jellyfish, sea turtles, seals, sea lions and stingrays thrive on the euphotic zone. The depth of this ocean is about 600ft.


Going down below the sunlit zone is the twilight zone or dysphotic zone. It is quite cold at this level. As there isn’t enough sunlight, plants cannot grow here. Marine life forms like octopus, lantern fish, rattalk fish, squid, viper fish and hatchet fish can be found in this zone. There are also few organisms that survive by emitting light on their own called bioluminescent organisms. This zone starts at about 600ft and extends to around 3000ft.


Deep down is the aphotic or midnight zone. Sunlight cannot reach this zone which has a depth of about 20,000 feet. It is completely dark and freezing cold with water pressure as much as two tons per square inch. Plants cannot survive here but still habitable to angler fish, tripod fish, sea cucumber, snipe eel, opossum shrimp, black swallower, and vampire squid.


ocean 1


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