Coral Reefs.qxd
Fact Sheets from the
Conservation Education Department
Coral Reefs
Coral reefs are diverse communi-
ties of marine plants and animals
that rise above sandy ocean floors
in some tropical areas of the world.
The mass of the reef is composed
of calcium carbonate (CaCO3), laid
down as the exoskeletons of ani-
Fast Facts
mals called stony, or hard, corals.
The surface of the reef is covered
More plants and animals
by the living part of the corals.
inhabit coral reefs than any place
The tentacled polyps of stony
else, except tropical rainforests
corals resemble anemones and
Coral reefs are the largest
belong to the same phylum,
structures on Earth.
Coral thrive in clear, shallow water, with an optimum
Cnidaria. Other members of this
Coral reefs are home to as
temperature of 24oC (75o F) .
large group include gorgonians (sea
much as one-quarter of all
whips and fans), fire coral, jellyfish,
about half of the weight of the
marine species.
and colonial anemone-like zoan-
coral body, and algal pigments give
thids. The tentacles on each coral
the coral its color. Since the algae
Key Terms
polyp have sticky, stinging cells that
play such a crucial role in coral sur-
help to stun and catch small animals
vival, without it, coral reproduction
Coral Bleeching -
that venture too close to the coral.
comes to a halt.
Occurs when poor water
When they come in contact with a
quality kills coral, leav-
bit of food, the tentacles pull it
Where Do Reefs Grow?
ing behind a colorless
down to the central mouth to be
Reef-building corals have very
skeleton.
digested. Many stony corals feed
specific requirements for growth
this way at night, then sink into the
that limit their distribution. The
Polyp - Soft, animal
protective skeleton during the day,
water must be clear, shallow, and
living inside hard,
while some other cnidarians feed
warm, with an optimum tempera-
stony coral.
during the day.
ture of 24oC (75o F) which is
All reef-building corals have algae
found in more tropical areas. Not
Zooxanthellae -
called zooxanthellae living inside
all water along the tropical coast-
Small plants living
their tissues. Through the process
lines is suitable for coral reefs, how-
in the tissue of
of photosynthesis, the algae convert
ever. Areas with high freshwater
reef-building coral.
carbon dioxide and water into oxy-
run-off, such as near the mouth of
gen and carbohydrates; these carbo-
Amazon River, lack corals. Corals
hydrates provide nutrients for the
require a salinity of at least 25 parts
coral polyp. The polyp, in return,
per thousand (ppt) and do best in
uses oxygen for respiration and pro-
full sea water (35 ppt). Coral reefs
vides carbon dioxide to the zooxan-
are generally restricted to the east-
thellae. Because these algae require
ern margins of continents where
light in order to perform photosyn-
warm water from the equator
thesis, their coral hosts are restrict-
arrives with the currents.
ed to relatively shallow (30 meters),
Consequently, coral reefs form off
clear water. The algae account for
the coast of Florida, but not off
the coast of California, where the
have a special adaptation, consisting
Coral Reef Conservation
water is much colder. The major
of a bony "beak" with teeth that
While the coral reef is one of
areas of reef development are in
are fused together into upper and
the most complex and diverse
the Caribbean and the Indo-Pacific
lower plates. This allows these fish
environments in the world, it is
regions. The largest reef in the
to graze on algae that grow on dead
also one of the most delicate.
world, the Great Barrier Reef, is
coral- as well as zooxanthellae in
Coral reefs are harmed by
located off the east coast of
live coral- by crunching pieces of
anchors from fishing boats, and
Australia, and covers a span of
the hard coral to get to the attached
divers and snorkelers standing
1,200 miles.
vegetable matter. The coral bits are
on reefs or collecting from
then ground in a bony mill located
them. Shoreline development,
Coral Reef Ecosystem
in the throat and returned to the
agricultural expansion, and
Red, brown, and green algae are
sediment in fine-grained form.
sewage problems in tropical
common on and around reefs.
This feeding strategy of parrotfish
areas can also kill reefs by caus-
They are frequently calcareous, lay-
creates much of the coral-derived
ing silt, sediments, and excess
ing down a layer of calcium carbon-
"sand" in and about the reefs. In
nutrients to wash into the sea.
ate (CaCO3) between their cells.
fact, one parrotfish can make up to
Coral bleaching has become a
Coraline red algae contribute to the
a ton of this coral sand per year.
serious threat to coral reefs
reef structure by acting as mortar
Since a coral reef is made up of
around the world. This happens
between the coral heads. Broken-
so many different kinds of fish and
when extreme changes in tem-
down calcareous green algae are a
invertebrate species, encounters
perature and salinity cause the
source of carbonate sand for sandy
between individual animals are
coral to expel the zooxanthallae,
bottoms and beaches.
common. Interactions between fish
leaving behind a colorless skele-
In addition to the corals, many
of different species are often
ton.
other animals feed, hide, and rest in
observed in the reef habitat. One
the complex reef habitat. Sponges
example of this is a cleaning sta-
What You Can Do!
in brilliant colors grow as both
tion. Smaller animals may appear to
Conserve water by using
encrusting patches and as freestand-
be "picking" or "biting" a larger
water-reducing fixtures, limit
ing shapes, including vase and bas-
one, with the "victim" doing noth-
shower time, and fix leaks
ket sponges. Some mollusks live on
ing to defend itself. This is actually
promptly.
the corals themselves, but many
cleaning behavior; the smaller fish is
Reduce rainwater runoff
more live in the sandy areas and
removing parasites, debris, or
through landscaping and
grass beds around the reef.
infected tissue from the skin of the
porous pavements.
Arthropods such as crabs, shrimp,
larger fish. The cleaner lives in a
Support sustainable use
and spiny lobsters hide in the many
semi-permanent territory called a
fisheries in food products.
nooks and crannies of the reef.
"cleaning station", which other fish
If you dive or snorkel,
Fish are the most prominent ani-
recognize. Both parties benefit from
don’t touch the coral - even the
mals of the reef. They exhibit glori-
this relationship: the larger fish gets
lightest touch with hands or
ous colors and fascinating ways of
rid of an irritant and the cleaner
equipment can damage sensitive
living. Many of them have seeming-
gets a meal without being harmed.
coral polyps.
ly strange body designs and/or
Cleaners include small fish such as
Don’t dump trash at the
social behaviors. These specializa-
gobies, cleaner wrasses, and young
beach or at sea; plastic bags and
tions provide efficient means of
porkfish, as well as many of the
other debris can injure or kill
feeding, schooling, and protection
shrimp that live in surrounding
marine animals. Try to retrieve
for a variety of fish, and enable all
sponges, anemones, and crevices.
fishing gear and equipment,
areas of the reef to be used as
Unique defense adaptations
especially monofilament line.
feeding, resting, or hiding places
among fish species is also a very
during the day and night.
important feature of coral reefs.
For example, the four-eye butterfly-
Coral Reef Fish
fish are thought to use fake eye-
The rock-hard skeletons of corals
spots to direct enemies to the
do not protect them from all of the
wrong end of the fish (the tail).
fish that inhabit the reef. Parrotfish
