Prey of Cnidarians ranges from animals several times larger than themselves to plankton.  Some Cnidarians are parasites and others obtain most of their nourishment from dissolved nutrients or endosymbiotic algae.  Predators of Cnidarians include starfish (the crown of thorns starfish can devastate coral), sea slugs, parrot and butterfly fish which eat corals and marine turtles who eat jellyfish.  Some jellyfish and sea anemones have symbiotic relationship with some fish such as clown fish that live among the tentacles of sea anemones and each partner protects the other against predators.