Coral Reef Symbiosis
Symbiosis comes from the words " sym " which means together and " biosis " which means life. Symbiosis occurs when two organisms create a union in which each is benefited by the other.
Coral lives a symbiotic life. Inside the sac of each coral polyp lives a one-celled algae called zooxanthellae (zoo-zan-thel-y). The algae gives off oxygen and other nutrients that the coral polyp needs to live and in return the polyp gives the algae carbon dioxide and other substances the algae needs. That is why coral reefs grow so near the surface of the water where it is the sunniest--the algae need sunshine for photosynthesis.
Many of the other plants and animals that live in and around the coral reef also have symbiotic relationships. Fish with troublesome parasites allow other fish to pick off the parasites. The parasitic fish get rid of the nasty bugs and the helper fish get a free meal.
Certain fish are immune to the sting of the jellyfish. That means the sting does not hurt them. They take shelter among the jellyfish's tentacles, thereby baiting a trap for other fish. In return, the fish get to share the meal with the jellyfish.
Some crabs will pick up sponges and seaweed and place them on their back. The crab is camouflaged from predators and the sponges and seaweed enjoy better food selection. Symbiosis helps to create the reef community.