Answer:
Option C, REEFS IN PERIL
Explanation:
Peril word signifies threat or immediate danger.
Since the reefs are under threat of extinction. The best heading that can justify the endangered reef species is the "option C" i.e Reef in Peril.
However, the other heading like THE FUTURE OF THE REEFS, BENEATH THE AZURE WATERS LIES A LOST COLONY etc. are also apt but one would not be able to understand that here the author is talking about the reef in danger.
