 Outbreaks are believed to occur in natural cycles, worsened by poor water quality and overfishing of the starfish's predators.The unsustainable overfishing of keystone species, such as the giant Triton, can disrupt food chains vital to reef life.Fishing also impacts the reef through increased water pollution from boats, by-catch of unwanted species (such as dolphins and turtles) and habitat destruction from trawling, anchors and nets.