Visualizing Environmental Science

Major Ocean Life Zones 281

Raul Touzon /NG Image Collection Tim Laman/NG Image Collection

Coral reefs are ecologically important because they
both provide habitat for many kinds of marine organ-
isms and protect coastlines from shoreline erosion. They
provide humans with seafood, pharmaceuticals, and
recreation and tourism dollars.
Sea grasses are flowering plants adapted to com-
plete submersion in salty ocean water. They occur only in
shallow water (to depths of 10 m, or 33 ft) where they re-
ceive enough light to photosynthesize efficiently. Exten sive
beds of sea grasses occur in quiet temperate, subtropical,
and tropical waters. Eelgrass is the most widely distributed
sea grass along the coasts of North America; the world’s
largest eelgrass bed is in Izembek Lagoon on the Alaska
Peninsula. The most common sea grasses in the Caribbean
Sea are manatee grass and turtle grass ( Figure 11.7).
Sea grasses have a high primary productivity and
are ecologically important in shallow marine areas.
Their roots and rhizomes help stabilize sediments, re-
ducing erosion, and they provide food and habitat for
many marine organisms. In temperate wa-
ters, ducks and geese eat sea grasses, and in
tropical waters, manatees, green turtles, parrot
fish, sturgeon fish, and sea urchins eat them.
These herbivores consume only about 5 per-
cent of sea grasses. The remaining 95 percent
eventually enters the detritus food web and is

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Turtle grasses form underwater meadows that are ecologically
important for shelter and food for many organisms. Photo-
graphed in the Caribbean Sea, the Cayman Islands.

decomposed when the sea grasses die. The decomposing

bacteria are in turn consumed by animals such as mud

shrimp, lugworms, and mullet (a type of fish).

Kelps, known to reach lengths of 60 m (200 ft), are

the largest and most complex of all algae commonly

called seaweeds (Figure 11.8). Kelps, which are brown

algae, are common in cooler temperate marine waters of

both the Northern and Southern Hemispheres. They are

especially abundant in relatively shallow waters (depths

of about 25 m, or 82 ft) along rocky coastlines. Kelps are

photosynthetic and are the primary food producers for

the kelp “forest” ecosystem. Kelp forests provide habitats

for many marine animals. Tube worms, sponges, sea cu-

cumbers, clams, crabs, fishes, and sea otters find refuge in

the algal fronds. Some animals eat the fronds, but kelps

are mainly consumed in the detritus food web. Bacteria

that decompose kelp provide food for sponges, tunicates,

worms, clams, and snails. The diversity of life supported

by kelp beds almost rivals that found in coral reefs.

The Neritic Province:

From the Shore to 200 Meters

The two main divisions of the pelagic environ-

ment are the neritic and oceanic provinces.

Organisms that live in the neritic province are

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Underwater kelp forests are ecologically important because they

support many kinds of aquatic organisms. Photographed off the

coast of California.

neritic province

The part of the

pelagic environment

that overlies the

ocean floor from the

shoreline to a depth

of 200 m (650 ft).