Under the clear blue sea, there are beautiful underwater cities that are rich in life. They have been around for millions of years and they hold communities of ocean creatures that live there. These 'cities' are coral reefs. Coral looks like rock, but it is actually made up of tiny clear animals called coral polyps. The bright colour of coral comes from tiny sea plants called algae. Coral and alage depend on each other to live. Coral may feel tough,but it is very sensitive. Today, many coral reefs are dying and there are many reasons why. First of all, the oceans are getting warmer. This kills the algae and so the coral reefs lose their colour and food. Water pollution,fishing with dynamite as well as the careless collection of coral also destroy coral reefs. If we do not take action, all the reefs will die in around 20 years. This will lead thousands of sea creatures to extinction. We can help save the world 's coral reefs to joining an environmental oranisation like Reef. lt 's worth a try!