Coral Reefs
A coral reef is an offshore ridge which is composed mainly of calcium carbonate. It is formed
from the secretions of small marine animals called coral polyps. Coral polyps thrive in shallow,
warm, nutrient poor, tropical waters. These tiny animals attach themselves to objects such as
rocks or existing reefs and build tiny shells of calcium carbonate around themselves. When coral
polyps die, new coral polyps build their shells on top of the old shells of the previous generation.
In this way the reef expands over time.
Types of Reefs:
Fringing Reefs:
- This type of reef forms along the shoreline in many tropical areas. The waters just offshore in
tropical areas are often ideal for coral growth. Coral reefs may form in the water close to shore.
There is usually a shallow lagoon between the reef and the shore. Many Caribbean islands have
fringing reefs including Barbados, Antigua, Tobago and St. Lucia.
Barrier Reefs:
-This type of reef may be several kilometers from shore. Barrier reefs start off as fringing reefs.
However, as sea level rises, the low lying areas near the coast are submerged. As the shoreline
moves back, the distance between the reef and the shore increases. If the reef grows upward
quickly enough to keep up with the rising sea level, it becomes a barrier reef. There is a wide
lagoon or shallow sea between the reef and the shore. The world’s largest barrier reef is known
as the Great Barrier Reef. It is found 50 to 250 kilometers off the coast of Australia and stretches
for over 2,600 kilometers. It is made up of over 2,900 individual reefs and about 900 islands. The
photo below shows a small section of this reef.
Atolls:
-A ring-shaped coral reef, islet or series of islets. This type of reef is found most often in the
Pacific Ocean. There are about four known atolls in the Caribbean Sea, three of which are
found off the coast of Belize.
Usually, the process of atoll formation begins when an undersea volcano rises above the
surface of the sea forming a volcanic island. If conditions are favourable, a fringing reef will
form around this island. Over millions of years, the island may recede into the ocean and
disappear completely, leaving behind a ring shaped coral reef ( an atoll) surrounding a
shallow body of water called a lagoon.
Conditions for Coral Growth:
Most coral reefs thrive in warm waters between 21-30 degrees Celsius
The water should be clear so that sunlight will be able to penetrate to where the coral is
growing. Thus most coral grows in relatively shallow water.
The water should contain the right amount of salt. Coral will not grow in areas where a
large amount of fresh water pours into the sea such as near the mouth of a river. (Salinity)
The water should be clean. Corals are sensitive to sediment and pollution. Muddy water
damages coral. Organic pollution, such as sewage, promotes the growth of other
organisms (such as seaweed or other algae) which may outcompete coral for space or
other resources.
The Importance of Coral Reefs:
A thriving coral reef is a colorful and spectacular sight. Reefs provide a home for many species
of marine life including sponges, algae, sea urchins, shellfish and fish. Many tourists visit
tropical areas hoping to observe and enjoy the beauty of the coral reefs and the creatures that live
there. Therefore, a thriving coral reef is an asset to the tourist industry in many tropical areas.
The abundance of marine creatures that inhabit coral reefs make them very important to our
fishing industry. There may be a hundred times more life on or near the reefs than out in the open
ocean.
A coral reef can also help to protect the coast by acting as a natural breakwater. Waves encounter
the coral reef before reaching the shore and are weakened as a result. Therefore, waves are less
likely to erode beaches which are protected by coral reefs. The World Research Institute has
determined that over 40% of St. Lucia’s coastline is protected by its coral reefs. Furthermore,
coral is slowly broken down by wave action into tiny fragments. These tiny fragments make up
much of the material on many of our beaches.
Coral reefs are very important natural resources. Therefore, it is very important that we protect
our coral reefs and ensure that they continue to thrive.
The video below shows scuba divers exploring coral reefs just off the coast of St. Lucia. Notice
the different types of coral and the many marine creatures which make the coral reefs their home.
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