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What is Coral?
Made by animals
Coral is made
by millions of tiny carnivorous (meat eating) animals called polyps.
Polyps live in groups called colonies.
Polyps
The polyp
is related to the anemone, and 
consists of a stomach with a mouth at one end. The
mouth is surrounded by a number of tentacles. These tentacles
resemble feet, which is how they get their name: 'polyp' is a
Greek word meaning 'many feet.'
The tentacles are covered with tiny stinging cells,and when a small creature brushes against the tentacles, it is killed. The prey is then brought into the stomach to be digested.
Polyps cannot
move from their limestone homes. They mostly feed at night.
How do polyps
reproduce?
A polyp reproduces
in either of two ways:
by dividing its own body to form two
polyps, or
by producing sperm and eggs
Just after the full moon in November, eggs and sperm are released
from coral polyps and float about for a few days. A small number
of eggs will fertilise, hatch into larvae, and settle on the reef
to begin new colonies.
Colonies grow rapidly.
One polyp can become a colony of 25,000 polyps in 3 years.
Building up a
Coral reef
Each polyp
builds a case of limestone around itself, using calcium from the
water. It is like a house, with a floor and walls. This remains
after it has died and forms a foundation for another polyp to
build a house on, putting a floor on the roof of the old one.
When these limestone formations increase, they are called a coral
reef.
In shallow water algae live in the tissues of the polyps . The algae use sunlight and the waste products of the polyp to make oxygen and food for the polyp. This kind of algae is called zooxanthellae. The algae need sunshine to survive, so do not live in deeper water where less sunshine filters through.
Coral reefs are the largest structures created by any group of animals in the world. They have existed on earth for over 200 million years. They grow in warm (18-33ºC), clear, fairly shallow water. The coral cannot grow in polluted water or water carrying soil from the land.
Coral Shapes
Coral colonies
have different shapes. The shape is 
determined by its environment. Coral that
is smooth and rounded grows in places where there is stronger
wave action, and branched coral generally grows in calmer, deeper
water. The limestone skeleton is white. The pieces of coral you
buy are dead coral that has been painted.
Different kinds
of coral reef
A fringing
reef is formed where coral polyps settle and grow close to
the shore. If the land sinks or the sea rises, the polyps build
upwards and a barrier reef is formed.
Atolls (islands of dead coral) form in a barrier reef surrounding
a sinking island. A lagoon is formed after the island has sunk,
with a ring of atolls around it.
Fish of coral
reefs
As many as 200 different kinds of fish may live
in one hectare of coral reef. They range in size from tiny gobies
about 10 millimetres long to 20 metre long whale sharks, the largest
fish of all. Coral reef fish have a great variety of shapes, which
depend on its feeding and habitat in the coral.
Read more about coral and coral reefs here
http://www.enchantedlearning.com/biomes/coralreef/coralreef.shtml
Go to kidcyber's page about Australia's Great Barrier Reef
Acknowledge this
source in your bibliography like this:
Sydenham & Thomas What is Coral?. [Online] www.kidcyber.com.au (2009)
October 2009 copyright © kidcyber [2009]