A new study by researchers at the ARC Centre of Excellence for Coral Reef Studies has found weed-eaters like parrotfish and surgeonfish can only keep coral reefs clear of weed up to a point. After the weeds reach a certain density, they take over entirely and the coral is lost.
For some years researchers have pinned their hopes on the ability of weed-eating fish to keep the weeds at bay while the corals recover following a major setback like bleaching, a dump of sediment from the land, or a violent cyclone.
However the latest work from James Cook University shows that once the weeds reach a certain density, the fish no longer control them, and prefer to graze less weedy areas.
Read more at James Cook University