15 July: Coral reefs

15th-21st July is Coral Reef Awareness week, so here are 10 things you might not know about them.

1. Corals are tiny animals, relatives of Jellyfish and anemones. An individual coral is known as a polyp. They are very simple creatures, consisting mostly of a stomach and a mouth with tentacles which it uses to catch and sting prey. A coral colony contains thousands of them. A coral reef is made up of the calcium carbonate exoskeletons of many colonies.
2. Even though they are animals, corals rely on photosynthesis to survive. They don't photosynthesise themselves, but have a symbiotic relationship with microscopic algae, or zooxanthellae, which live in their stomachs. 90% of the energy a coral needs comes from the zooxanthellae and only 10% from hunting prey.
3. Coral reefs are the largest biological structures on Earth. The largest of them, Australia’s Great Barrier Reef, can be seen from space and covers an area of 133,000-square miles. That said, reefs cover less than 1% of the ocean, which in total adds up to an area about half the size of France.
4. Everybody knows the Great Barrier Reef is the largest. You may not know which is the second largest, though. It's Mesoamerican Barrier Reef, which stretches over 550 miles from Cancun to Honduras.
5. Nevertheless, coral reefs are home to around a quarter of all marine species, and are sometimes called "rainforests of the sea". They provide a protected environment for sea creatures to live and to spawn. Sea mammals such as dugongs also raise their young in reefs.
6. There are three types of coral reef: fringing reefs, barrier reefs, and coral atolls. Atolls are often mistaken for islands. Barrier reefs and fringing reefs form around coastlines, the difference being that fringing reefs occur closer to the land.
7. Reefs tend to form on the eastern side of land masses, because the eastern side is usually warmer. Reefs need a temperature of 70 to 85º Fahrenheit to survive. For the same reason, they tend to grow in shallow seas - at a maximum depth of around 150 feet, because shallower water is more easily warmed by the sun, which is also needed for photosynthesis. They also like strong currents and wave patterns, because these deliver more food.
8. Scientists have recently discovered that many parts of a coral reef can be harvested to make medications to treat cancer, arthritis, human bacterial infections, Alzheimer’s disease, Heart disease, Viruses, and other diseases.
9. Corals actually like eating plastic. Scientists in North Carolina collected corals and fed them a variety of things including sand and tiny bits of plastic, and found they really liked plastic, especially microplastics that weren't covered in Bacteria.
10. Around 60% of the world's coral reefs are threatened by human activity, although they are valuable to us - they protect shorelines from storm damage, and are also important for fishing and tourism. Destroying just 1 kilometre of coral reef causes a loss of between $137,000 to $1,200,000 over a 25-year period, according to the World Resources Institute. However, humans can also help the coral along. Old navy ships are sometimes sunk because coral reefs will start to grow on them. It's also possible to raise young corals in a protected environment and plant them on a reef when they have passed their most vulnerable stage. This is called "coral gardening".