Coral Reefs

• Corals are tiny animals called polyps that live in colonies, called reefs.
• Coral skeletons are cups of calcium carbonate which join together forming limestone.
• Coral must have a base to grow on, rocks on the seabed and shipwrecks are adequate.
• The Great Barrier reef, that is off of the NE coast of Australia is 2600km long, has 3000 separate reefs, covers 350,000 square km and has taken 5 million years to grow.
• Their are 800 types of coral
• Reefs are a habitat for over 25% of earths marine speices.
• Polyps and algae have a symbiotic relationship, which is called zooxanthellae. Algae lives inside polyps and the use of carbon dioxide and water the polyps provide. This allows photosynthesis, allowing coral to respire.
• Bleached coral is the white skeleton of dead coral
• Fringing reefs have low and narrow bands of coral which forms a platform connected to land. Forms a lagoon on wave side.
• On the wave side of reefs, there is always more growth due to the wave action that occurs there. It provides oxygen and food.
• Barrier reefs are similar to fringing reefs but are further from land. They have large lagoons, due their distance from the coast and coral cannot survive there. They are usually fringing reefs that have grown outwards.
• When the island completely subsides beneath the water leaving a ring of growing coral with an open lagoon in its centre, it is called an atoll. Atolls usually form on sinking volcanic foundations. They are far from the coast line, and survive in deep water.
• Darwin's theory of reefs is that all three reefs (Fringing, barrier, atoll) are linked. Fringing turn into barrier due to coral growing outwards. He believed that atolls used to be barrier reefs around a sinking island, and the coral has grown upwards to access light.
• The distribution: Pacific dominant, more in global south and within 30 degrees of the equator. But, despite latitude, ocean currents can cool waters down meaning they aren't fit for reefs. An example of this is the Peru cold ocean current that runs of the west coast of South America.
• For coral reefs to grow the temperature must be above 18 degrees
• Cold sea currents don't allow coral to grow, despite latitude. For example Peru is affected by a sea current which inhibits growth.
• Coral cannot grow in waters deeper than 30m due to the need for photosynthesis and their food source of plankton.
• The outer edge of reef grows highest due to wave action providing oxygen and nutrients
• Salt levels must be high in order for coral to grow
• Coral must be below the tidal range, if coral is exposed to air it dies.
• Coral must have clean and sediment free water in order to grow in order to photosynthesise.
• Coral provides a vast ecosystem and therefore aids the fishing industry. LIC's coral reefs account for 1/4 of fish catches
• Coral provides chemicals that can be used in medicines to treat tumours and be bone grafts