Coral reefs 3
Coral reefs 3Coral reefs are one of the oldest types of living systems on earth, and certainly one of the most spectacular. They are massive underwater structures formed by the limestone skeletons of tiny invertebrate animals. Reefs house a greater diversity of body forms, chemistry, and animal phyla (thirty-two compared to the eight that inhabit the most biodiverse ecosystems on land). Phyla comprise the second largest category of living things, after kingdoms.
Coral animals begin life as free-floating larvae, but settle on the sea floor in sedentary colonies. The term "coral" applies both to these animals and to their skeletons, particularly the skeletons of stone-like corals.
Many different organisms, including molluscs, sponges, and worms, help shape reefs, but hard corals and various algae are the major architects. In effect, the corals build limestone, because their skeletons are made of Calcium Carbonate. The skeletons deposited by these corals and other organisms accumulate, along with sand and other debris, to form the backbone of the reef. Over tens of thousands of years, chemical and mechanical changes turn the reef into true rock.
The body of a coral animal consists of a polyp, which is the living portion of the coral. A polyp is a hollow, cylindrical structure attached at one end to a surface, the other end is a mouth surrounded by tentacles which gather food and can sting prey to paralyse it. Polyps live in colonies, which grow from 1 to 7 inches, depending on the species. Coral polyps are classified as animals. Microscopic algae live within the animal tissues in a symbiotic relationship. The algae turn sunlight into carbon and sugars, which are then available to the polyp. In turn the polyp filters particles out of the water and excretes waste (nitrogen and phosphorus) that becomes available to the symbiotic algae. It's this very tight nutrient recycling within the coral itself that allows these corals to live in very low-nutrient waters.
There are three kinds of reefs: atolls, barrier reefs, and fringing reefs. Atolls are formed out in the middle of the ocean by volcanic subsidence, while fringing and barrier reefs form near continents. Florida contains both of these kinds of reefs, not as far offshore as Australia's Great Barrier Reef, but not terribly close either. Most are eight to eleven kilometres (five to seven miles) offshore. All three kinds of reefs can have associations, called patch reefs, which are small, shallow-water clusters or offshoots. In Florida, patch reefs can be as close as one hundred meters to the shore. Ancient limestone reefs have occupied the Florida peninsula intermittently over the past 150 million years. Florida's present coral reefs came into existence 5,000 to 7,000 years ago, when sea levels rose following the Wisconsin Ice Age. The reefs in the Florida Keys are part of the third largest barrier reef system (360 square kilometres from Miami to the Dry Tortugas).
Coral reefs are continuously being both built up and decomposed, so different parts of...
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