Coral Reefs - International Reading Association

y Joanna Solins
Types of Coral Reefs
Types of Reefs
Barrier Reef
Dive down into clear tropical water, and you’re
likely to find a rich and beautiful ocean community.
Rainbow-hued fish flit around complex structures in
a wide array of shapes, sizes, and colors. Some look
like brains, and others like fingers. Some look like deer
antlers. Others sway fanlike in the ocean currents. You
are looking at a coral reef.
Coral reefs are found in warm, shallow waters around
the world, but especially in tropical areas along the
coast and on the fringes of volcanic islands. Some
coral reefs, called atolls, are ring-shaped. They form
on top of underwater volcanoes.
From a distance, coral reefs can look like rocky
underwater islands covered with plants. Get up
close, though, and you’ll find that the “rocks” are
alive. Many of the “plants” are really animals. These
structures are all created by tiny, simple animals
called corals.
Coral Atoll
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Octocoral
Corals are related to jellyfish. Their bodies are water-filled sacs.
They have a mouth surrounded by stinging tentacles. Unlike
jellyfish, though, adult corals do not move around. Instead, they
build cup-shaped skeletons to protect their soft bodies. Reefbuilding
corals live in large groups called colonies. A single colony
can contain thousands of individual animals, called polyps.
Different species of coral grow in different patterns, forming the
variety of shapes on the reef. The colonies grow larger as some
polyps die off and leave their skeletons behind. New polyps then
create skeletons on top of the old ones. Large reef-building colonies
may grow less than one inch per year.
Coral polyps use their stinging tentacles to catch tiny organisms
that float by. They have another important source of food, too,
though. Coral polyps have algae living in their bodies. The algae
can use the sun’s light to create energy, just like plants. In return
for nutrients and a safe place to live, the algae give the polyp
oxygen and nutrients that it needs. Algae can provide a coral polyp
with more than half of its energy. The algae also give the coral its
beautiful colors. Most corals must live in shallow, clear water so
that the algae can get enough sunlight.
Elkhorn Coral
Pink Coral
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Coral reefs are important for many reasons. They support a huge
diversity of life. Though they cover less than one percent of the ocean
floor, they are home to about 25 percent of ocean species. That’s more
than a million different species! Humans rely on reefs, too. Reefs are
home to fish that people eat. Reefs also protect beaches and coastal
communities from pounding ocean waves during storms. They provide
income for many people through the tourism they create.
Unfortunately, coral reefs are in danger. Careless divers, people
who collect coral, and poor fishing practices all damage reefs directly.
Pollution from coastal developments and fuel from boats are large
problems, too. They can poison the coral and make the water cloudy.
In cloudy water, the algae living in the coral can’t get enough sunlight.
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Coral Bleaching
Healthy coral with plant-like algae living
inside polyps
Bleached coral with algae being released
from polyps
One of the biggest problems facing coral reefs today
is called “coral bleaching.” Under certain types of stress,
corals can lose their algae. The term “bleaching” is
used because corals appear white without algae. If
conditions return to normal quickly, corals can replace
algae and recover. Otherwise, they die.
Scientists do not understand coral bleaching very
well yet. They know that warmer water temperatures
cause corals to bleach, but they don’t know why. One
theory is that the warmer water stresses the coral. It
produces fewer nutrients for the algae, so the algae
leave. Another theory is that the warm water stresses
the algae. The stressed algae produce less oxygen,
and the coral releases them.
Whatever causes the algae to leave, though, there
have been many more coral bleaching events in recent
years. Many people believe that global warming is to
blame. When humans burn fuel, gases are released
into the atmosphere. These gases trap heat. Many
scientists now agree that all of the heat-trapping gases
in our atmosphere are causing the global temperature
to rise. Even a small rise in temperature can cause
bleaching, so global warming is a threat to corals.
People around the world are working to help coral
reefs. You can, too. If you are lucky enough to visit
a reef, make sure that you learn how to enjoy it
without causing damage. Never take home a coral
souvenir.
Even from home, you can make a difference. By
conserving energy and reducing trash and pollution,
you can improve the environment for coral reefs.
Dead coral skeleton covered with thread-like
algae or plants growing on the outside
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