Predation on massive corals: are devastating population outbreaks of Acanthaster planci novel events?

Abstract

Coral communities on many reefs of the central third of Australia's Great Barrier Reef have been subject to major damage by population outbreaks of the crown-of-thorns starfish twice since the 1960s. The interval between outbreaks on individual reefs was c15yr. This study compares size and damage frequency distributions of major taxa of scleractinian reef corals of massive morphology on two sets of six reefs of this region. One set of reefs had experienced major population outbreaks of A. planci, one set had not. On both reef sets, representatives of the familes Faviidae, Poritidae and Mussidae comprised c90% of the massive corals, though members of the Faviidae predominant on non-outbreak reefs and Poritidae predominant on outbreak-affected reefs. Massive coral asemblages on outbreak reefs possessed only 1/3 of the colonies on unaffected reefs and approximately half of the surviving corals on the outbreak reefs exhibited damage of >1/3 their colony surface areas. Few large (old) colonies occurred on the outbreak reefs, whereas such large corals were common on unaffected reefs. As most massive corals are slow-growing, long-lived and have lower rates of recruitment than corals of other morphology, continuing starfish reinfestation coincident with reestablishment of a coral cover by the faster-growing, more opportunisitc corals will not allow sufficient time for recovery of the massive coral assemblages. They will be replaced by algae and non-massive coral assemblages in the intervals between outbreaks. The recent devastating outbreaks appear to be abnormal perturbations coincident with large-scale human activities on the Great Barrier Reef. -from Authors