Living coral (2/3)
Rainforests of the sea
Coral reefs, like one at Hanauma Bay, function as rainforests of the sea. They house a diverse population of fish and other sea creatures. There is a delicate balance between the health of reef and the health of the animals that live there. Just like in the rainforest, the entire ecosystem depends on each other part.
The hard coral polyps grow in nutrient-poor water. They provide a habitat for the fish and other marine life that live there. If the coral were not there, the waters would be unproductive and deserted. Coral initiates a process called “nutrient cycling” that supports the creatures in the bay.
The nutrient cycling process ensures that fewer nutrients are needed to support the entire community. The Earth does not constantly receive nutrients like it receives sunlight. There is only so much to go around, and warm tropical waters are not generally very nutrient rich to begin with. The coral bed in the bay acts as a nutrient reservoir. It collects nutrients that are vital to the life of the ecosystem, and then releases them into the water for the rest of the creatures to use. This function is vital to the life of the entire bay. Without the coral bed performing the nutrient cycling process, life in that area would not be possible at all.
How coral reefs grow
Coral reefs are made from coral colonies, which are derived from millions of polyps working together in cooperation. The reef that we see with our eyes is representative of generation after generation of skeletal remains from the previous polyps.
Coral actually begins its life as free-floating larvae. After a period of time, these larvae attach themselves to a hard surface to become a polyp. The polyps reproduce asexually, and are able to form colonies from themselves. The coral colonies begin to grow, and can reproduce both sexually and asexually. This allows new polyps to form rather quickly.
Each polyp can be as large as a saucer or as small as the head of a pin, depending on the variety. An individual polyp consists of tentacles, a mouth and a gut. They eat by trapping plankton and microscopic algae with their tentacles as it passes by. This is why gentle wave motion is vital to the growth of coral.
As the coral colonies begin to form they extract calcium and carbonate from the water. They each build an external skeleton to protect them. This skeleton is under a thin layer of tissue. As the older polyps die, new polyps build on top of them.
Over each year, millions of coral polyps create their own skeletons, and this creates a coral reef. It may take up to 100 years for a coral reef to grow just three feet. The reef at Hanauma Bay represents thousands of years of coral growth.