Crown-of-thorns starfish on the great barrier reef

During the 1960s and 1970s the bulk of the hard coral cover of reefs in the central region of Australia's Great Barrier Reef was killed as a result of population outbreaks of the coral-eating starfish, Acanthaster planci. Millions of starfish were involved. Renewed outbreaks have recently been noted on reefs where extensive recolonization has occurred since the mid-1960s, giving rise to concern that reefs in the region will be impoverished for long periods of time. The causes of the population outbreaks are unknown, but there is evidence of human involvement in triggering the population outbreaks.