Where do Corals live?

Coral reefs are found in over 100 countries.  Most reefs are located between the tropics of Cancer and Capricorn, in places such as the Pacific Ocean, the Indian Ocean, the Caribbean, the Read Sea and the Arabian Gulf.  Corals are also found farther from the equator in places where warm currents flow out of the tropics, such as Florida and southern Japan.  Worldwide, coral reefs cover an estimated 284,300 square kilometers (110,000 square miles).Coral reefs grow best in waters with a temperature of between 21 and 29 degrees Celsius (70 and 85 degrees Fahrenheit).  It is possible for soft corals to grow in hotter and colder places, but growth rates under these conditions are very slow.  Corals prefer clear and shallow waters, where lots of sunlight filters through to their symbiotic algae.   It is possible to find corals at depths of up to 91 meters (300 feet), but reef-building corals grow poorly below 18-27 meters (60 to 90 feet).  Corals also grow poorly near river openings or coastal areas with excessive run-off, because corals need salt water to survive.

How long does it take for coral to grow?

Corals grown at different rates, depending on water temperature, salinity, turbulence, and the availability of food.  The massive corals are the slowest growing species, adding between 5 and 25 millimeters (.2 inches to an inch) per year to their length.   Branching and Staghorn corals can grown much faster, adding as much as 20 centimeters (8 inches) to their branches each year.

How do corals get their shape?

The variety of shapes and sizes of coral colonies largely depends on their location and species.  Some species form hard, pointed shapes, while others form soft, rounded shapes.  The shape of coral colonies also depends on the location of the coral.   For example, where there are strong waves corals tend to grown into robust mounds or flattened shapes.  In more sheltered areas the same species may grow in more intricate shapes such as delicate branching patterns.

How do Coral Polyps eat?
Coral polyps eat in two different ways, depending on their species.  Many coral polyps are nourished in a unique way by a tiny algae called zooxanthellae (pronounced zo-zan-THEL-ee).  The algae live within coral polyps, using sunlight to make sugar for energy, just like plants.  Zooxanthellae process the polyp's wastes to retain important nutrients and in turn provide the polyp with oxygen.  Meanwhile, the coral polyps provide the algae with carbon dioxide and a sage, protected home.   Zooxanthellae living with the tissue of hard corals can supply them with up to 98 percent of their nutritional needs.Another way that corals eat is by catching tiny floating animals known as zooplankton.   At night the polyps come out of their skeletons to feed, making the reef look like a "wall of mouths".  The polyps stretch out their long, stinging tentacles to capture the zooplankton that are floating by.  The captures plankton are then put into the polyp's mouths and digested in their stomachs.

How do corals get their colour?

Most coral polyps have clear bodies and their skeletons are white, like human bones.  Most corals get their colour from the zooxanthellae inside them.   Several million zooxanthellae live in just one square inch of coral and produce pigments.  These pigments are visible through the clear body of the polyp and give the coral its beautiful colour.

How do Corals reproduce?

Coral reproductive methods vary, depending on the species.  Some species such as brain and star corals are hermaphrodites, meaning they produce both sperm and eggs at the same time.  Other corals, such as Elkhorn and boulder corals, are gonochoric, meaning that they produce single-sex colonies.  In these species, all of the polyps in one colony produce only sperm and all of the polyps in another colony produce only eggs. Coral larvae are formed in two different ways.  The larvae are either fertilized within the body of a polyp or outside the polyp's body in the water.   Fertilization of an egg within the body of a coral polyp is achieved from sperm that is released through the mouth of another polyp.  The sperm and egg merge and form a planula larvae, which matures inside the body of its mother.  When the larva is ready, it is "spit" into the water through the mouth of its mother.   Other species of coral reproduce by ejecting large quantities of eggs and sperm fertilize in the water.  This process is called coral spawning.  In some areas, mass coral spawning events occur on one night a year and scientists can predict exactly when this will happen.  Trillions of eggs and sperm are simultaneously released into the water in one of the most astounding acts of synchronicity in the natural world. Once in the sea, larva are naturally attracted to light.  They swim to the surface of the ocean, where they remain for days or even weeks.  If predators do not eat the larva during this time, they fall back to the ocean floor and attach themselves to a hard surface.  An attached planula metamorphasizes into a coral polyp and begins to grow and divide itself in half, making exact genetic copies of itself.   As more and more polyps are added, a coral colony develops.  Eventually the coral colony becomes mature, begins reproducing and the cycle of life continues!

What do Corals need to survive?

• Sunlight:   Corals need to grow in shallow water where sunlight can reach them.  Since corals depend on the zooxanthellae (algae) that grow inside of them and this algae needs sunlight to survive, corals too need sunlight to survive.  Therefore, corals rarely develop deeper than 50 meters (165 feet).
• Clear Water:    Corals needs clear water to survive and don't thrive well when the water is opaque.  Sediment and plankton can cloud the water which decreases the amount of sunlight that reaches the zooxanthellae.
• Temperature:   Reef building corals require warm water conditions to survive.  Different corals living in different regions can withstand different temperature fluctuations.  However, corals generally live in water temperatures ranging from 20 to 32 degrees Celsius (68 to 90 degrees Fahrenheit).
• Clean Water:   Corals are sensitive to pollution and sediment.  Sediment can settle on coral, blocking out sunlight and smothering coral polyps.  Pollution from sewage and fertilizers increases nutrient levels in the water, harming corals.  When there are too many nutrients in the water, the ecological balance of the coral community is altered.
• Saltwater:    Corals need saltwater to survive and require a certain balance in the ratio of salt to water.  This is why corals don't live in areas where rivers drain fresh water into the ocean.