Stony corals are the kind that built coral reefs. Coral reefs can be one of the bubbliest places on earth. Reefs are home to 25% of all marine life on the planet and cover less than 1% of the ocean floor. Corals are mainly found in shallow warm waters because they rely on the sun to grow and produce oxygen.
Corals are alive. They are made up of tiny animals that are called polyps, these are distant cousins of jellyfish. Thousands of polyps can make up a coral. Coral polyps are incredibly delicate and very slow growing. The fastest species of branching coral only grows at 10cm a year. Whereas other corals take years to grow a few millimeters. Coral colonies can reach immense sizes and are tremendously long-lived. There are colonies alive today which are believed to be over 700 years old!!
Polyps have a unique partnership with tiny algae called Zooxanthellae. These algae are photosynthetic. Using the energy of the sun they produce 95% of the food the corals need: Oxygen, sugars and fats. The corals on their turn provide the algae with carbon dioxide, phosphorus and nitrogen. This mutual relationship is called a Symbiotic Relationship. The algae are also responsible for the colors of the corals.
On the menu for corals are also microscopic plankton and tiny small fish that happen to be floating by. Corals catch their prey through their stinging tentacles.
Reefs which form close to land, following the contours of the coastline, are called fringing reefs.
Where the reef is separated from land by a lagoon or open water, it is called a barrier reef.
Coral reef atolls are almost exclusively a feature of the Pacific, where they form rings of coral up to several kilometers in diameter around open sea or sandy islands.
The coral reefs of the Dutch Caribbean are very diverse. Bonaire has fringing coral reefs which encircle their islands. Starting in very shallow water, the reefs slope gently seaward to around 30 feet (10m) before dropping down to depths in excess of 200 feet (60m).
Despite enormous differences between coral reefs, they all have the same basic needs, they need:
– warm water,
– clear water,
– sunlit water,
– absence of sediment, which could choke and kill them,
– and a hard substrate on which to grow.
Coral reefs are only found in tropical seas where the year-round water temperature is between 18 – 30’C, or broadly speaking between 30’ north and 30’ south of the equator.
What exactly is coral? The answer might surprise you.
Geplaatst door ABC Science op vrijdag 29 december 2017