Coral Reefs: The Rainforests of the Sea

Coral reefs start out small and grow about half an inch a year, but if undisturbed by man they can grow to be quite large. The Great Barrier Reef off the northeast coast of Australia is 150 km (93.2 mi) wide and 2000 km (1,242 mi) long! The tan parts of the reef are the shells of dead coral polyps and the colorful parts are the living parts of the reef.

Reefs grow best in sunny, shallow, clear water. The water must be clear and shallow so that the reef can get lots of sunlight. They rarely grow deeper than 40m and they prefer salt water, doing poorly in areas where there is a lot of river runoff due to the freshwater as well as the silt which can cover a reef or muddy the water blocking the sunlight. The best temperature for coral reefs is between 25 and 31û C and the best salinity is between 34 and 37 parts per 1000. The appropriate temperatures and salinities are most often found in the tropics.

Reefs grow best in sunny, shallow, clear water. The water must be clear and shallow so that the reef can get lots of sunlight. They rarely grow deeper than 40m and they prefer salt water, doing poorly in areas where there is a lot of river runoff due to the freshwater as well as the silt which can cover a reef or muddy the water blocking the sunlight. The best temperature for coral reefs is between 25 and 31û C and the best salinity is between 34 and 37 parts per 1000. The appropriate temperatures and salinities are most often found in the tropics.

Fringing reefs grow in shallow water along the shore and prefer arid climates with limited river runoff. Fringing reefs are platforms that are continuous with the shore. That means they grow right up to the edge of the shore, like in the picture above.

Barrier reefs are separated from the shore by a wide, deep lagoon. They grow only when there has been a change of sea level on the adjacent coast. This occurs when a fringing reef grows upwards so that it can stay near the surface of the water. Coral reefs like to grow just below the waterline so that they have the best access to the sunlight. It is best if a reef grows at the same rate as the rise of the water. Barrier reefs also grow where the land is sinking faster than the water. The number of barrier reefs has increased dramatically as the greenhouse effect has warmed up our atmosphere causing the water levels to rise.

Atolls are reefs surrounding a lagoon. They are created when an island surrounded by barrier reefs sinks below the ocean surface, leaving a circular reef, called an atoll. Atolls are also created when water levels rise to cover an island and the surrounding reef grows to keep up with the surface of the water.