This large starfish gets its name from the venomous, long spines that cover its body. They live among and feed on coral polyps. When the species becomes overpopulated, it can destroy vast coral reef ecosystems. In fact, widespread destruction of the Great Barrier Reef is partly blamed on these sea stars, which have experienced a population explosion over the last decade or so. The outbreaks are likely due to pollution from agricultural runoff, creating algae blooms that allow the crown-of-thorns' natural predators to get a less-thorny and easier meal elsewhere. During outbreaks, the starfish feed on adult corals and prevent the maturation of young corals.