of the ocean, the scientists define different regions by depth (Figure14.6).
Figure 14.5: The Trieste made a record dive to the Challenger Deep in 1960. No craft exists
today that can reach that depth. ( 7 )
Sunlight only penetrates water to a depth of about 200 meters, a region called thephotic
zone(photic means light). Since organisms that photosynthesize depend on sunlight, they
can only live in the top 200 meters of water. Such photosynthetic organisms supply almost
all the energy and nutrients to the rest of the marine food web. Animals that live deeper
than 200 meters mostly feed on whatever drops down from the photic zone.
Beneath the photic zone is theaphotic zone,where there is not enough light for photo-
synthesis. The aphotic zone makes up the majority of the ocean but a minority of its life
forms. Descending to the ocean floor, the water temperature decreases while pressure in-
creases tremendously. Each region is progressively deeper and colder, with the very deepest
areas in ocean trenches.
The ocean can also be divided by horizontal distance from the shore. Nearest to the shore
lies theintertidal zone. In this region, you might find waves, changes in tide, and constant
motion in the water that exposes the water to large amounts of air. Organisms that live in
this zone are adapted to withstand waves and exposure to air in low tides, by having strong
attachments and hard shells. Theneritic zoneincludes the intertidal zone and the part of
the ocean floor that very gradually slopes downward, the continental shelf. Lots of oceanic
plants live in this zone, since some sunlight still penetrates to the bottom of the ocean floor
in the neritic zone. Beyond the neritic zone is theoceanic zone, where the sloping sea floor
takes a much even steeper dive and sunlight does not reach. Animals such as sharks, fish,