Parrotfish do not intentionally harm coral when they feed on it. Rather, they feed on the algae that grows on the coral, using their strong beaks to bite off small pieces of coral and grind them up along with the algae. This helps to keep the coral clean and free of excess algae, which can otherwise grow out of control and smother the coral.
In fact, parrotfish play an important role in the health of coral reefs by controlling the growth of algae. Without herbivorous fish like parrotfish to feed on algae, coral reefs can become overrun with algae, which can harm or kill the coral.
However, overfishing of parrotfish or other disturbances to coral reefs can disrupt the balance of species and lead to problems such as coral bleaching or the proliferation of harmful algae. It is important to manage coral reefs in a sustainable way in order to protect the health of these ecosystems.