Answer:
The correct answer is - mutualism.
Step-by-step explanation:
Like it is given here, The coral gives a protected environment for algae and other compounds algae required for photosynthesis. Photosynthesis performed by the algae provides a byproduct of microscopic algae.
These algae produce oxygen and help the coral to remove wastes and algae is important to the survival of the coral animals, which use the energy to extract calcium from the seawater and build their calcareous skeletons.