Inspire Biology

Pelagic

zone

Abyssal

zone

Benthic

zone

Plankton

Photic

zone

Aphotic

zone

The

benthic zone

is the area along the ocean floor that consists of sand, silt, and dead

organisms. In shallow benthic zones, sunlight can penetrate to the bottom of the ocean

floor. As depth increases, light and temperature decrease. Species diversity tends to

decrease with depth, except in areas with hydrothermal vents, where shrimp, crabs,

and many species of tubeworms are found. Many species of fishes, octopuses, and

squids live in the benthic zone.

Figure 24

Producers are found mainly in the photic zone. Consumers live in the pelagic (photic and aphotic)

and benthic zones.

Coastal ocean and coral reefs

One of the world’s largest coral reefs is off the southern coast of Florida. Coral reefs are

among the most diverse ecosystems. They are widely distributed in warm shallow

marine waters. Coral reefs form natural barriers along continents that protect shorelines

from erosion. The dominant organisms in coral reefs are corals. When you think of

coral, you might picture a hard, stony structure, but this is only the framework secreted

by tiny animal polyps. Corals are soft-bodied invertebrates that live in the stonelike

structures.

Most coral polyps have a symbiotic relationship with algae called zooxanthellae (zoo

uh zan THEL uh). These algae provide corals with food, and in turn, the coral provides

protection and access to light for the algae. Corals also feed by extending tentacles

to obtain plankton from the water. Other coral reef animals include species of

microorganisms, sea slugs, octopuses, sea urchins, sea stars, and fishes.

Lesson 3 • Aquatic Ecosystems