Distinctive Characteristics
There are many general characteristics specific to coral reefs all around the world. Overall, most coral reefs are rather young; formed less than 10,000 years ago. As coral reefs are formed, they grow upwards with the rising water levels so they can get adequate levels of sunlight to survive. Predominantly, coral reefs are formed by coral polyps (skeletons of coral) and calcareous algae (chalky algae containing calcium carbonate) which help to strengthen the reef's resistance from natural or human threats. There are three main types of coral reefs: fringing reefs, barrier reefs, and atoll reefs. Fringing reefs (as pictured above) are often found attached to the coast, or slightly separated from the shore by a shallow channel of water. Barrier reefs are typically separated from shore by a deep lagoon or channel, while atoll reefs are generally stretch around a lagoon in a circular shape but not surrounding a main island. In addition to these, there are about nine other minor categories for the classification of coral reefs.