Corals are polyps of coelenterates (cnidarians) that contain numerous algae in their tissues. The algae contain photopigments which give the corals their color. When stressed by high temperatures, water pollution, or similar shocks, many corals expel their algae and turn white, a process called "coral bleaching." This appears to help the coelenterates survive the initial shock, but if they do not recover their native algae quickly, they soon die. Similarly, the algae cannot live for long outside of the coelenterates bodies. Based on this information, the relationship between the two organisms is most likely __________.