About 20 years ago it was noticed that many of these reefs were dying back. An important cause? Increased sediment discharge from those same
rivers you were talking about... apparently clearing vegetation, runoff from cities and agriculture was doing the damage. My brother is a builder and it's law that he take great care about sediment control from his building sites, as is the case with many other sediment generating activities. This is not news in North Queensland. The prospect of lead, mercury, cadmium etc... in seafood isn't exciting either. Apparently trace elements in anaerobic sediments become bioavailable after they're dredged up then get concentrated up the food chain. This happened during the 80's a few hundred kilometres south in Gladstone and closed a fishery. (I've attached a paper documenting this elsewhere in this thread).