EANHS Bulletin 30(1) 
28 
Coral polyp begins to buila (much enlarge $ 
other places the reef is separated from 
the shore by an area of water, called 
the lagoon 
The reef is made by tiny coral 
animals. Each coral animal, called a 
polyp, is small and soft. But it can take 
minerals from sea water and build a 
wall around itself Together, millions 
and millions of coral polyps build the 
massive coral reef. 
Each coral polyp is like a little sea 
anemone: a tube-shaped body with 
tentacles at one end. The base of each 
coral polyp is divided into many fine 
sections. And all around itself, the 
polyp builds walls of lime (calcium 
carbonate). 
A coral colony begins with a coral 
larva from a fertilised egg. The larva 
drills in the sea. then lands on a solid 
surface From its base, the larva begins 
to build a star- shaped stony foundation 
It continues to build, making a stony 
cup around itself. 
The coral animal, now 
called a polyp, buds into 
more polyps. Each polyp 
continues to build, 
forming a coral colony. 
When polyps die. other 
polyps build over and 
around them, 
There are many kinds 
of corals, each building a 
different kind of stony 
shape Many corals are 
rounded masses. Others 
are like plates, like 
branching horns, or like 
mushrooms in shape. 
The polyps live in 
their stony homes. They 
spread their tentacles out over the stony 
cups They catch and eat tiny plankton 
creatures. When they arc not feeding, 
they pull their tentacles back inside 
their stony homes. 
Some polyps are so small that you 
can hardly see them in the stony mass 
Other polyps are large, and may be 
brightly coloured When they die. you 
can see the holes where they lived, 
with a starlike pattern on the bottom. 
Many coral polyps have single- 
celled algae living inside their 
tentacles These algae are called 
zooxanthellae The tiny algae make 
food in sunlight through 
photosynthesis. They help to feed the 
coral polyps and to give them their 
bright colours Scientists think that in 
some way the algae also help the corals 
to get the calcium carbonate to build 
their stony homes. 
The coral reef is not smooth. It is 
