The Great Barrier Reef
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WHAT ARE CORAL REEFS?
THE GREAT BARRIER REEF
Coral reefs are among the world’s most biologically
diverse ecosystems. They are also one of the most
endangered. Coral reefs are made of corals, which
are large groups of small animals called polyps. The
polyps live in a calcium carbonate skeleton. They
have an opening in their center that has tentacles,
which they use to feed on phytoplankton in the water
around them1. Coral reefs are generally found in clear,
tropical waters, and they usually are found from the
water’s surface to about 150 feet deep, because they
need sunlight for survival. Coral reefs house
approximately 25% of the life in the ocean, yet they
only make up about 1% of the ocean floor2.
The Great Barrier Reef is one of the most magnificent
wonders of the natural world, with its distinctive colors
and beautiful wildlife, combined with its vast array of
marine animals. It is home to more than 1,500 species
of fish, 4,000 types of mollusks, and more than 200
species of birdlife5. It started forming over 5 million
years ago6. It is more than 260 kilometers from the
coast of Australia at its most distant point. Aside from
its physical attraction, the Great Barrier Reef also acts
as a wave buffer for Australia, preventing erosion,
property damage, and even death7. The Great Barrier
Reef is sensitive to climate change, changes in wave
and current movement, and physical damage. Events
such as El Nino, the building of breakwaters, and
runoff from the land can have negative effects of the
Reef system8. The Great Barrier Reef is home to
thousands of species, such as sea urchins, sponges,
sea stars, shrimp, lobster, crabs, fish, sharks,
dolphins, whales, octopuses, snails, and many more.
It is also home to many species of bird, who feed on
the plant and animal life in the reefs.
THREE TYPES OF CORAL REEFS
There are three types of coral reefs: fringing reefs,
atolls, and barrier reefs. Fringing reefs line the
shoreline of land masses, and they are most
commonly found in areas like Hawaii and the
Caribbean. Atolls are a series of low coral islands
surrounding a central lagoon, and are most commonly
found in areas like the Indo-Pacific. Lastly, barrier
reefs are found farther from the shoreline in areas like
the Indo-Pacific and the Caribbean3. They are usually
separated from land by a lagoon, and sometimes, they
grow parallel to the coast4.
The largest reef in the world is the Great Barrier Reef off
the coast of Australia, which is over 1,200 miles long
(“Coral Reefs Biome”). It is not a continuous reef, and it
contains over 2,800 individual reefs, of which 760 are
fringing reefs (“World Heritage”).
FISH OF THE REEF
There are over 1,500 species of fish in the Great
Barrier Reef. Some examples are clown fish, butterfly
fish, parrotfish, snappers, cod, grouper, eels, and
many more. The overall structure of fish is
streamlined, and fish vary greatly in size, shape, and
color. The color patterns on the fish act as a warning
to predators that they may be poisonous, or it can
camouflage them so they can better hide from their
predators and their prey. The smallest fish of the Reef
is the goby, which is one centimeter long and weighs
less than a gram, and the largest fish of the Reef is
the giant cod and grouper that can weigh almost 4,000
kilograms. Most of the fish on the Reef range in size
from 1 centimeter to 3 meters. These fish feed on
what is most available, ranging from algae to other
fish. They also eat plankton. Fish are free-swimmers,
and use their fins to maneuver through the ocean
water. The life span of fish in the reef is hard to
determine, especially for the smaller, preyed on fish. If
a fish can survive being eaten, it can live for quite a
while.
and generally glide along the bottom looking for food.
They eat mollusks and crustaceans in the sand. They
have moveable eyes, and their mouth is located on
their underside. They use electro-receptors to locate
their prey. Rays also have flat plates in their jaws,
which they use to crush the shells of their prey before
they eat them. They are also camouflaged to help
prevent predation.
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CRUSTACEANS
There are a variety of crustaceans in the Great Barrier
Reef. These include shrimp, lobsters, crabs, and
mollusks. They range in size from 1 centimeter to 50
centimeters.
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SHARKS AND RAYS
Sharks and rays are very closely related. Sharks and
rays can range in size from 10 centimeters to 13
meters. There are about 350 species of sharks and
425 species of rays worldwide. They are both freeswimmers, with sharks using their fish to move
through the water. Sharks have streamlined bodies,
which help them move fast and turn quickly. Scientific
investigations have showed that sharks have
denticles, which help them move through the water
faster by reducing drag from the water around them.
They are also counter-shaded for camouflage. Most
sharks are predators, feeding at dusk or after dark,
and they use their rows of razor-sharp teeth to kill their
prey. They feed on fish, squid, sea urchins,
crustaceans, and even other sharks.
Rays, on the other hand, are shaped like flattened
disks with a long tail. They are also free-swimmers,
Shrimp
They are among the most diverse and active animals
on the Great Barrier Reef. They are free-swimming,
and they sometimes burrow in the sand to hide from
predators. They have claws that help them catch their
prey. They eat other crustaceans, small fish, and
some feed on plants.
Crabs & Lobsters
Lobsters are the most commonly encountered species
on the Reef. They have large, developed claws that
inflict pain on their prey and on humans. They feed on
other crustaceans, fish, and plants. They vary in size.
Crabs also vary in size, shape, and color. They have
tentacles that help them find their way around the
ocean. They live in their shells, under the water and
on land. They are scavengers, and feed on dead or
decaying things. They usually walk sideways, but
some swim.
The decorator crabs specialize in
camouflage, sticking bits of sponge,
algae, and other bits and pieces
onto their body. They are hard to
see, unless they move.
Mollusks
The Great Barrier Reef is home to between 5,0008,000 mollusks. Mollusks are soft-bodied animals that
have a hard shell for protection. They vary incredibly
in terms of shapes and forms, but they all have a
general structure: a head, and a body supported on a
single muscular “foot” that helps them move through
the water. Some mollusks do not have shells.
Examples are octopuses, squid, and sea slugs.
Because these do not have a shell, they defend
themselves from predators by being brightly colored or
very unpleasant tasting. Some even spray ink or a jet
of water.
pores that trap food particles carried by the passing
water. They range from microscopic to 1 meter in size.
They come in many different shapes and colors. They
have an amazingly developed array of chemical toxins
that ward off predators. They usually attach
themselves to rocks, hard-shelled animals, or
seaweed. They can repair and regenerate very easily.
They are also very helpful in the process of building
up coral reefs, because they bore into rocks, shells, or
corals and help in bio-erosion.
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SEA CUCUMBERS
There are approximately 1,150 species of sea
cucumbers worldwide. They range in size from 1
centimeter to 60 centimeters. They are shaped like a
big sausage. They do not really have a shell, but they
have protuberances that act as body armor for
protection. Some species are camouflaged to look like
rocks on the seafloor. They have tentacles that they
use to mop up particles for food. They spend their
time lying on the seafloor or burrowing in the sand.
They are immobile until the sun sets. Sea cucumbers
eat tiny scrap particles, wiping their tentacles over the
sediments on the seafloor to get food.
As a defense mechanism, sea
cucumbers can throw up their
entire digestive system! This
distracts their predators, which
usually goes for their regurgitated
food instead of them. It then takes
the sea cucumber a couple months
to grow its digestive tract back in
its entirety.
WHALES
Whales are warm-blooded mammals. They have
streamlined bodies and compact flippers that help with
balance, steering, and movement through the water.
Whales can reach up about 15 meters in length. They
are divided into two groups: those with teeth (called
toothed whales) and those without teeth. There are
also the baleen whales, which use baleen plates to
get their prey from the sea. Baleen whales eat krill,
plankton, and small fish. Examples are the blue whale,
humpback whales, and right whales. Toothed whales,
such as the sperm whale and killer whale, eat sharks,
seals, dolphins, birds, squid, and fish. Whales breathe
through their lungs, and therefore, surface regularly to
breathe. They also produce high-pitched sounds for
communication purposes. Humpback whales produce
“songs” that can last for hours.
SPONGES
There are approximately 1,500 species of sponges in
the Great Barrier Reef. They are bottom-dwellers.
They are loose colonies of cells, with an outer wall of
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AUSTRALIAN PELICANS
Pelicans are very large birds, and the Australian
Pelican is the largest of the seven species of Pelicans.
They are characterized by long bills and a massive
throat pouch. Their bills are usually 40-50 centimeters
long. The Australian Pelican also has the largest beak
of any bird in the world. They weigh anywhere from 46.8 kilograms and are 1.6-1.8 meters long. They have
massive wings, with a wingspan of 2.3-2.5 meters.
Fish are the main part of the Pelican’s diet, but they
also eat crustaceans, tadpoles, and turtles. They do
hold food in their beaks, but only for a short period of
time. Impressively, they can live between 10- 25 years
or more9 10!
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Coral reefs are being destroyed at
an alarming rate. It is estimated
that 10% of the world’s coral reefs
have already been destroyed. This
destruction is due in large part to
humans. Things like pollution,
sewage, irresponsible fishing, poor
tourism practices, erosion, and
global warming damage these
beautiful habitats (“Coral Reef
Biome”). The Great Barrier Reef is
endangered, as well, and needs to
be protected, along with all the
world’s beautiful coral reefs.
WATER PROPERTIES IN THE GREAT
BARRIER REEF
Coral reefs need water between 68-82 degrees
Fahrenheit, which is often located along the eastern
shores of land. They usually develop in areas with a
lot of wave action, because the waves bring in food,
nutrients, and oxygen. They also prevent sediment
from falling on the reef. Reefs need calcium to grow,
which is usually more readily available in warm,
tropical waters11. Reefs usually have nitrogen and
phosphorus of some form in their waters. Production
of the Great Barrier Reef is partially controlled by
dissolved inorganic nutrients, like nitrogen and
phosphorus, which are taken up by the phytoplankton
in the Reef and converted into organic matter12. The
water of the Great Barrier Reef is very warm, with
much available sunlight, and the water is generally
very salty and low in nutrients. The Great Barrier Reef
has a tropical climate. The area is characterized by
strong tidal currents, which are usually semi-diurnal
with diurnal inequality towards the north. The
maximum tidal range is about 3 meters by the coast,
and increases from the coast to about 6-9 meters
farther out. The water is vertically mixed for most of
the year, but is affected by stratification due to
freshwater input during January to April13. The waves
bring in and deposit sediments on the ocean floor,
such as rocks and sand. The rocks and sand are
home to many organisms in the reef, such as sponges
and crustaceans that burrow in the sand.
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"Why Care About Coral Reefs?" U.S. Coral Reef Task Force. 13 Apr. 2006
<http://www.coralreef.gov/coralreefs/index.html>.
1
2
"Coral Reefs Biome." 12 Apr. 2006 <http://www.nceas.ucsb.edu/nceas-web/kids/biomes/coral/htm>.
3
"Coral Reefs Biome." 12 Apr. 2006 <http://www.nceas.ucsb.edu/nceas-web/kids/biomes/coral/htm>.
Categories and Structure of Coral Reefs. University of Virginia Islands. 12 Apr. 2006
<http://www.uvi.edu/coral.reefer.structre.htm>.
4
"Great Barrier Reef." Culture and Recreation Portal. 13 Apr. 2006
<http://www.cultureandrecreation.gov.au/articles/greatbarrierreef/>.
5
6
"Corals>Ecology." 2006. World Wildlife Fund. 12 Apr. 2006 <http://www.worldwidelife.org/coral/ecology.cfm>.
7
"Coral Reefs." Congressional Digest 82.7 (2003): 199-224. 12 Apr. 2006 <http://web2.epnet.com>.
"Great Barrier Reef." Culture and Recreation Portal. 13 Apr. 2006
<http://www.cultureandrecreation.gov.au/articles/greatbarrierreef/>.
8
Text Box:
"Coral Reefs Biome." 12 Apr. 2006 <http://www.nceas.ucsb.edu/nceas-web/kids/biomes/coral/htm>.
"World Heritage: Great Barrier Reef." World Heritage. 5 Feb. 2006. Department of the Environment and Heritage. 13
Apr. 2006 <http://www.deh.gov.au/heritage/worldheritage/sites/gbr/index.html>.
"ReefED-Animals." GBR Explorer. 2003. Great Barrier Reef Marine Park Authority. 13 Apr. 2006
<http://www.reefed.edu.au/explorer/animals>.
9
"Who's Who." Reef Education Network. 2001. The University of Queensland. 12 Apr. 2006
<http://www.reef.edu.au/contents/fr_who.html>.
10
Text Box:
"Coral Reefs Biome." 12 Apr. 2006 <http://www.nceas.ucsb.edu/nceas-web/kids/biomes/coral/htm>.
11
"Coral Reefs Biome." 12 Apr. 2006 <http://www.nceas.ucsb.edu/nceas-web/kids/biomes/coral/htm>.
12 "Environmental Status: Water Quality." Great Barrier Reef Marine Park Authority. 13 Apr. 2006
<http://www.gbrmpa.gov.au>.
Protected Areas Programme." 5 Jan. 2001. UNEP World Conservation Monitoring Centre. 13 Apr. 2006
<http://www.wcmc.org.uk/protected_areas/data/wh/gbrmp/html>.
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