All About Coral Reefs

The coral reef is one of the most beautiful places on earth, but sadly they are dying. For example, in Mexico, a mysterious disease was wiping out lots of the coral and fish. Also, as climate change rages on, when the coral gets too hot, they release the algae that live in their cells and provide them with nutrients, turning the corals white and sometimes causing them to starve. This usally causes the surrounding fish to die as well.

In other news, a coral reef is an underwater ecosystem containing reef-building coral. Reefs are formed of colonies of ‘coral polyps’ which hold together with calcium carbonate. Most coral reefs are built from ‘stony corals’, whose polyps cluster in groups. There can also be ‘artificial reefs’, which are formed when  some sort of man made machine (such as a boat or car) sink into the ocean, and over time coral begin to form on them. When fish see the brightly-coloured stuff, they automatically go there.

As crazy as it may sound, corals are actually living! Their family includes sea anemones and jellyfish. Unlike sea anemones, corals have hard carbonate exoskeletons that support and protect the coral.
Most reefs grow best in warm, shallow, clear, sunny and agitated water. Coral reefs first appeared 485 million years ago, at the dawn of the Early Ordovician, displacing the microbial and sponge reefs of the Cambrian.

Sometimes called rainforests of the sea, shallow coral reefs form some of Earth’s most diverse ecosystems. They take up less than 0.1% of the world’s ocean area, about half the area of France, yet they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms, sponges, tunicates and other cnidarians. Coral reefs flourish in ocean waters that provide few nutrients. They are most commonly found at shallow depths in tropical waters, but deep water and cold water coral reefs exist on smaller scales in other areas.

Most coral reefs were formed after the last glacial period when melting ice caused sea level to rise and flood continental shelves. Most coral reefs are less than 10,000 years old. As communities established themselves, the reefs grew upwards, pacing rising sea levels. Reefs that rose too slowly could become drowned, without sufficient light. Coral reefs are found in the deep sea away from continental shelves, around oceanic islands and atolls (a ring-shaped coral reef). The majority of these islands are volcanic in origin. Others have tectonic origins where plate movements lifted the deep ocean floor.

Darwin’s theory starts with a volcanic island which becomes extinct. As the island and ocean floor go down, coral growth builds a fringing reef, often including a shallow lagoon between the land and the main reef. The subsidence continues, and the fringing reef becomes a larger barrier reef further from the shore with a bigger and deeper lagoon inside. Ultimately, the island sinks below the sea, and the barrier reef becomes an atoll enclosing an open lagoon.