Page 68 - Oceans

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coral reefs and atolls

The clear waters of tropical oceans contain few of the

nutrients that are essential to oceanic life, yet they support
one of the richest ecosystems on Earth—tropical coral reefs.
Their living wealth is based on a partnership between
simple animals called corals and microscopic, plantlike
organisms that make food using the energy of sunlight, just

like phytoplankton. The growing corals form massive living
reefs, populated by a dazzling diversity of animal life.

≤ Reef coRals
Corals are animals that are closely related to sea anemones. Reef crest Lagoon
They have the same cylindrical bodies crowned with BUIlDING Reefs >
stinging tentacles for catching small animals. Many live in Since they need sunlight, reef
interconnected colonies, including tropical reef-building corals live in clear, shallow water. Limestone Reef debris
corals, which are unique because they have microscopic Their soft bodies are supported by Reef face Coral Base Reef flat
plantlike zooxanthellae living in their tissues. These are skeletons of limestone, which build
supplied with vital nutrients by their hosts, and in return up into rocky reefs. These reefs have
they use solar energy to make food that the corals need.
steep sides facing the open ocean,
but often enclose shallow lagoons. Bedrock
Lettuce
coral
Massive star Brain coral
coral Seagrass
Red
Sea fan coralline
algae
Branched
elkhorn coral
Flattened
star coral
Sea whip

Lagoon is dominated
by sand and seagrass

Reef flat is sheltered,
but the water is often
very warm and salty

Reef crest is colonized
by red coralline algae
that cements coral
fragments together
> Reef ZoNes
The reef face
is colonized by
strong corals that can
withstand ocean waves.
Broad, flattened types grow in
deeper water, while branching corals Reef face is exposed to the
are common near the top. The reef crest, open ocean, but has the
where waves break, is a mass of coral fragments richest diversity of corals coral
cemented together with red coralline algae, a type
of seaweed. Behind this lies the sheltered reef flat,
which often gives way to a sandy lagoon.