Life Zones in the Ocean

I. Horizontal zones (those extending from land out to sea).

A. Coastal Zone: that region in which tides expose the sea bottom for some part of each day. The habitats are alternately submerged under salt water and waterlogged for hours and then exposed to the air and dried out for hours. Also known as littoral, nearshore, and intertidal zone.

B. Pelagic Zone: located seaward of the coastal zone’s low-tide mark, this contains the vast open waters of the ocean. Two subdivision are recognized:

a. Neretic Zone: the water overlying the continental shelf. With the exception of Antarctica, these waters usually extend to a depth of 600 ft. Sunlight penetrates the entire water column.

b. Oceanic Zone: The region of the sea extending from the edge of the continental shelf, over the continental slope, and over ocean floor. It is characterized by darkness and tremendous pressure. Vertical life zones are significant here.

II. Vertical life zones of the oceanic zone.

A. Neustic zone: the thin film or “skin” formed by surface tension at the surface of the water

B. Euphotic  zone: The top of the water column as far down as light is available for photosynthesis. Depending upon water clarity, the bottom of the euphotic zone is about 500 ft below sea level. Also known as epipelagic zone.

C. Aphotic zone: the remainder of the water column below the euphotic zone. Food chains usually begin with detritus or living algae and bacteria sinking from above.  This zone is further subdivided by depth as follows:

Mesopelagic zone: 500 to 3,280 ft below the sea surface.
Bathypelagic zone: 3,280 to 13,000 ft below the sea surface
Abyssopelagic zone: 13,000 to 20,000 ft below the sea surface
Hadal zone: 20,000 to 35,000  ft below the sea surface.

III. Benthic Zone

This zone contains all the habitats of the sea bottom, whether in coastal, continental shelf, or deep sea environments. Organisms may live within the bottom material or on its surface.

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