[vaughanb]

Decades ago the reef was endangered by run-off from agriculture (fertilisers, agri-chemicals etc) and I believe this has been managed, since it's largely under human control (ie, we could stop song them tomorrow if we wanted).

There have occasionally be natural predators too, like the Crown of Thorn starfish.

The current threat to the reef is ocean warming -- a vastly different threat. There is not much humans can do in the short term to mitigate the problem.