Recovery of reefs from crown-of-thorns starfish outbreaks

Crown-of-thorns starfish on dead coral Photo: CRC Reef

Coral reefs recover from outbreaks of crown-of-thorns starfish in a similar way to their recovery from other impacts that reduce coral cover, such as cyclones or coral bleaching. Even on the most heavily damaged reefs, some corals remain alive. As these corals grow, they begin the process of reef recovery. The rate at which a reef recovers from predation by crown-of-thorns starfish depends on many factors including the rate of recruitment of corals to the reef, and the impacts of cyclones and runoff from the land.

Many coral species spawn only once a year in a mass spawning in spring or early summer (October to December). Eggs and sperm are released into the water where they combine and eggs are fertilised. Coral larvae can be carried long distances from the parent colonies by currents and tides.

Recent research has shown that some reefs are more likely than others to receive large numbers of coral larvae from distant reefs in ocean currents. The reefs which receive large numbers of larvae can have many young corals growing on them within a few years after of an outbreak. As a result, coral cover can return to the normal level within about 10 years. Other reefs that do not receive a plentiful supply of coral larvae will take considerably longer to recover, perhaps 15 years or more.

Although coral cover on an individual reef can reach levels that are considered normal on the Great Barrier Reef, the same combination of coral species may not be present as existed before the outbreak. Some species appear quickly after a reef is damaged and grow rapidly. Other species are slower to appear and slower growing. These corals may not reach previous levels on the reefs for some decades. This change in species diversity is one of the concerns if the interval between outbreaks becomes shorter than the time required for the coral community to completely recover. In this situation, reefs might lose some biodiversity and be dominated by a small number of those coral species that can recover rapidly.