Ocean Zones

The benthic realm extends from the shoreline to the deepest parts of the ocean floor. The section of the shoreline above the high tide line is known as the supralittoral, supratidal, or "splash," zone. It is actually covered by water only during the highest tides of the year. The next lower region of the shoreline, between high and low tide, is referred to as the littoral, or intertidal, zone. The portion of the seafloor below low water, extending outward to the edge of the continental shelf, is the sublittoral, or subtidal, zone. Typically, the base of the sublittoral zone corresponds to the base of the euphotic zone. (Some classifications use the term littoral to refer to the entire shore zone, from the supratidal to subtidal zones of the continental shelf.) The floor of the continental slope, extending from a depth of about 650-13,200 ft (200-4,000 m), is defined as the bathyal zone. The bathyal zone includes all of the dysphotic zone and the upper aphotic zone, so it is a dark and foreboding place. The abyssal plains, flat, nearly featureless expanses of ocean floor at depths ranging from 13,200-20,000 ft (4,000-6,000 m), occupy the abyssal zone. Finally, the deepest parts of the ocean bottom, within the ocean trenches, are defined as the hadal zone.

The benthic realm is an especially rich environment for living organisms. Scientists now believe that up to 98% of all marine species (not individuals, but species) are found in or near the ocean floor. Some of these are fish or shellfish swimming just above the ocean floor, but most are organisms that burrow in the sand or mud, bore into or are attached to rocks, live in shells, or simply move about on the ocean floor.

In the deeper parts of the ocean floor, below the euphotic zone, no herbivores (plant eaters) can survive. However, the "rain" of dead organic matter from above still supports thriving bottom communities.