Some corals that are only inches tall can be hundreds of years old. Coral reefs are important ecosystems not only for corals but also for many other species whose larval forms and juveniles develop in the shelter of the reef. Some of the major sources of damage to reefs currently are overfishing and fishing with cyanide. The effect of overfishing is to allow the overgrowth of algae, which blocks the light from the corals and thereby kills them. Silt from terrestrial deforestation causes additional blockage of the light.
Coral mining is very destructive because explosives are used to extract specific materials.
Improperly treated sewage also causes problems for coral reefs by promoting excessive algae growth to smother the corals. The runoff of pesticides and fertilizers from adjacent urban areas poisons many of the organisms that should be living on the reef. To find out the current status and what is predicted for the near future of coral reefs, look at the Home Page for your textbook to find a reference to coral reefs. Write a short description of what your have learned, and what the future scenario will be for the world's coral reefs. The following terms describe stages in the sexual life cycles of the Cnidaria.