some natural threats to coral reefs are hurricanes and natural disasters increase in temperatures of the water and tidal Emerson low tide that exposes heads of coral.
over fishing, fishing using cyanide and dynamite and killing sea turtles for meat and there shell are all human threats to coral reefs
Blast fishing or dynamite fishing is the practice of using explosives to stun or kill schools of fish for easy collection. This often illegal practice can be extremely destructive to the surrounding ecosystem, as the explosion often destroys the underlying habitat (such as coral reefs) that supports the fish.
A boater might litter into the reef or go over a reef and break some of the coral. A driver could because they could have a fuel spill and the fuel will go into the ocean. As well some times the boaters take the fish to sell like in Nemo.
By not littering. Help clean oil spills use less water and to help reduce pollution walk bike and even ride the bus. That is how we can protect coral reefs.