Mother Nature Network: Although they only take up a tiny fraction of space within the planet's oceans (about 0.1 percent), coral reefs are some of the most diverse ecosystems. They are home to about 25 percent of all marine species, including fish, crustaceans, mollusks, marine worms and, of course, the cnidarians that are responsible for building the reef's stony coral infrastructure. These intriguing cnidarians create these expansive reefs by settling upon seabeds and secreting calcium carbonate to serve as exoskeletons...