Answer: The correct answer is -
Presence of photosynthesizing algae.
Explanation:
Corals are dependent upon algae (such as zooxanthellae) that provides large amount of nutrients ( such as organic carbon) and oxygen (through photosynthesis) that is required for its growth. Also, it plays significant role in the lives of marine ecosystem (such as small and large fishes).
Thus, a wide variety of color is observed in the coral bed because of presence of photosynthesizing algae.
