Coral reefs are diverse underwater ecosystems formed over millions of years by corals secreting calcium carbonate. They occupy less than 1% of ocean area but are home to 25% of marine species. Coral polyps secrete limestone shells and rely on algae called zooxanthellae for food, allowing reef growth. There are two main reef types - fringing reefs near shore and barrier reefs separated from land by lagoons. Coral growth requires warm, clear, sunlit water at optimal depths between 20-40 meters with normal salinity and gentle waves.

1. Coral Reefs
Mr Johnson

2. What are Coral Reefs?
Coral reefs are diverse underwater ecosystems held together by calcium
carbonate structures secreted by corals
• They occupy less than 0.1% of the world's ocean surface, about half the area of
France
• They provide a habitat for 25% of all marine species
• Because they are so diverse, coral reefs are often called the rainforests of the sea.
• Coral reefs are also very important to people. The value of coral reefs has
been estimated at 30 billion U.S. dollars and perhaps as much as 172 billion U.S.
dollars each year.
• They provide food, protect the shorelines, provide jobs based on tourism, and
even medicines.

3. What are corals
• Corals are ancient animals related to jellyfish and anemones
• An individual coral is known as a polyp, a very small and simple organism
consisting mostly of a stomach topped by a tentacle-bearing mouth.
• The polyps extend their tentacles at night to sting and ingest tiny organisms called
plankton and other small creatures.
• They secrete calcium carbonate creating a protective shell made of limestone in
which they live
• When coral polyps die, new coral polyps build their shells on top of the old shells
of the previous generation.
• The shells from these and other marine animals build up over million of years to
form coral reefs

4. Zooxanthelae
• Reefs only occur in shallow areas that are reachable by sunlight because of the
relationship between coral and a algae called zooxanthelae
• The coral provides the algae with a protected environment and compounds they
need for photosynthesis. The algae then photosynthesize and pass the food they
make from the suns energy to the coral.
• It is this relationship that allows corals to grow fast enough to build the enormous
structures we call reefs. The zooxanthellae also provide much of the color that
corals have. Zooxanthellae can provide up to 90% of a coral’s energy
requirements
• In many ways, reef-building corals are animals that act like plants – they stay in
one place and get some of their energy from the sun.

5. The brownish-green specks are the
zooxanthellae that most shallow,
warm-water corals depend on for
much of their food.
Diagram showing a cross section
of a coral polyp. The polyp is
shown sitting in its calcium
carbonate shell with its tentacles
outstretched.

6. Types of Coral reef in the Caribbean
There are two types of coral reef in the Caribbean, each found on a different type of
landform. They are fringing reef and barrier reef
• Fringing reef: This is the most common type in the Caribbean. The reef lies close to the
shore and the water between the reef and the shore is shallow. Many Caribbean islands
have fringing reefs including Barbados, Antigua, Tobago and St. Lucia. Jamaica has an
almost continuous fringing reef along its western, northern and eastern coastlines.
• Barrier reef: This lies further away from the shoreline and is separated from land by a
deep lagoon. This type of reef may be several kilometres from the shore. The world’s
largest barrier reef is known as the Great Barrier Reef. It is found 50 to 250 kilometres
off the coast of Australia and stretches for over 2,600 kilometres. It is made up of over
2,900 individual reefs and about 900 islands. The barrier reef located off the coast of
Belize is the second largest in the world at 200 km long

7. Example of Fringing reefs

8. A section of the Belize
barrier reef
Example of a barrier reef
A part of the great
barrier reef

9. Conditions necessary for coral reef formation
Coral reefs will grow only where conditions are suitable. They must be an area with a
tropical climate. However, they need much more than just warm sun. The following are
ideal conditions for coral growth
• Temperature- tropical corals only live in varying temperatures 18 to 30 degrees Celsius
but these are the extremes. The ideal temperature is between 23 and 25 degrees Celsius.
Cold water slows the growth but if the water is too warm it bleaches the corals
eventually killing them.
• Light -sunlight is necessary for photosynthesis. The alage (zooxanthelae) that provides
food for the coral requires the suns energy in order to carry out photosynthesis
• Clear water: The water must be clean, clear and well oxygenated: clear water enables
sunlight to penetrate easily. Water that is polluted or carries a lot of sediments is not
suitable. The sediments makes the cloudy, preventing sunlight from penetrating the sea
water. Sediments also choke the corals

10. Conditions necessary for coral reef formation
• Corals grow best at depth of 20-40m: this allows for the penetration of sunlight
(light penetration becomes difficult below 100m). The depth of water also affects
temperature, as temperature decrease with depth of water
• Normal seawater salinity, together with gentle wave movement: The water
should contain the right amount of salt. corals will not grow where the water is
not salty enough e.g. at the mouth of a river or where it is too salty, e.g. in some
parts of the Red Sea. The water must be a sea water with a salinity of around
3.5%

11. References
• http://oceanservice.noaa.gov/education/kits/corals/coral02_zooxant
hellae.html
• http://www.defenders.org/coral-reef/basic-facts
• http://en.wikipedia.org/wiki/Coral_reef
• http://ocean.si.edu/corals-and-coral-reefs