Dredging stirs up a lot of mud, which takes time to settle. Nature also does this on a grander scale, but not continuously.
The outer reef is not at risk from dredging. If it was, then natural river outflows would have stopped it from ever forming in the first place. Hard corals must have very low nutrient water, where algae find it hard to multiply. Hard corals cannot compete against algae and the like.
Inshore soft corals are much more tolerant of algae, and high nutrients. They are mostly phototrophs, so turbidity for too long blocks sunlight. Just like plants.
Sea grass and mangroves require plenty of nutrient. Thus you normally find dugongs in fairly turbid water. Mangroves are typically plentiful around river deltas. I wonder why?
Fertilizer runoff from farms needs to be looked at more competently than it has been, recently. While lots of N and P would be bad for the outer reef, there is no way it can get out there. Inshore, it is less clear that there is much damage. Places like AIMS and JCU have neither the money nor the competence to perform such complex surveys over such large areas.
