Explanation:

• Coral reefs are large underwater structures composed of the skeletons of colonial marine invertebrates called coral.
• Corals extract calcium carbonate from seawater to create a hard, durable exoskeleton that protects their soft, sac-like bodies. These exoskeleton remains of millions of corals pile up with time to form coral reefs. 
• The corals have a symbiotic relationship with photosynthetic algae called zooxanthellae.
• These algae live inside the coral polyp's body and provide the coral with food. The polyps, in turn, provide a home and carbon dioxide for the algae.
• These algae are responsible for the variety of colours of corals.

Hence both statements are correct.