I've been learning about life on coral reefs. Recently I've become aware of the damage to coral reefs caused by tourism and inexperienced divers: 1) Corals have a thin membrane which keeps them healthy. Touching them could break this membrane, causing infection which can lead to death. 2) Stepping on, leaning on, and sitting on coral could smash their polyps.
I am not against being responsible as a diver, respecting nature, arriving and leaving without a trace. I'm just curious what the difference is between human and animal contact. Parrot fish eat coral, taking bites out of it, leaving exposed areas and this damages the coral. I've seen footage of sharks having feeding frenzies on reefs, where they smash into the reef during the commotion and while trying to catch their prey. Fish rub up against coral and peck at them to get algae, and crustaceans walk on the coral with legs that seems like it would break the thin protective membrane on the coral.
Obviously, as humans we technically do not belong in their world, so I'm sure there are reasons for damage with that alone; but why does marine life causing damage not cause actual damage? Or does it, and it just repairs differently or faster somehow?