GREAT BARRIER REEF
// Outlook Report 2014
3.6.2 Outbreaks of crown-of-thorns starfish
Crown-of-thorns starfish are a major predator of coral. An adult crown-of-thorns starfish can consume up to 478 square centimetres (about the size of a dinner plate) of coral each day.245 Under natural conditions, it is thought that crown-of thorns starfish populations increase to outbreak concentrations in a 50 to 80 year cycle.246 However, human impacts may have increased the frequency and severity of outbreaks.246 Over the past half-century, they have occurred from 1962 to 1976, 1978 to 1990, and 1993 to 2005247 and there is currently another outbreak concentrated between Lizard Island and Cairns. An outbreak of crown-of-thorns starfish is considered to be occurring when they are at densities greater than about 30 starfish per hectare.248,249 Outbreaks of crown-of-thorns starfish are one of the major causes of coral cover decline in the Region14 (see Section 2.3.5). Each outbreak has resulted in severe reductions in coral cover on a regional scale, particularly in the central area of the Region.14 Outbreaks appear to initiate in the area between Lizard Island and Cairns, and gradually progress south over several years,250 although independent outbreaks have been observed in the Swain Reefs in the far south (Figure 3.13). There are indications that increased nutrient loads contribute to crown-of-thorns starfish outbreaks due to increased food supply and therefore survival of their larvae (Figure 3.14).246,252,253 Importantly, the increased frequency of outbreaks, combined with other stresses on corals14, means coral populations are increasingly unable to fully recover before the next outbreak occurs.
3.6.3 Introduced species
Introduced species are non-native plants or animals that have arrived in an environment outside their normal distribution. They can have severe negative consequences for local native species and habitats. In the marine environment they are normally transported attached to the hulls of ships, in ballast water, via visits to islands or occasionally through aquaculture operations. Introduced species have been found in both the Region’s marine and island ecosystems.
Figure 3.13 evidence of crown-of-thorns starfish outbreaks, 1985–2013
unpublished data. 251
The map shows areas where evidence of a crown-of-thorns outbreak has been detected as part of the Australian Institute of Marine Science Long-term Monitoring Program. Reefs with an outbreak detected have shown evidence of an active outbreak, an incipient outbreak or recovery from an outbreak. ‘Not detected’ refers to surveyed reefs with no signs of a crown-of-thorns outbreak within the survey period. Source: Australian Institute of Marine Science Long-term Monitoring Program,
Changes in ecosystem conditions may have resulted in more frequent outbreaks of crown-of-thorns starfish.
Figure 3.14 potential role of nutrients in the population dynamics of crown-of-thorns starfish
al. 2010 246, Brodie et al. 2005247, Furnas et al. 2013254
Crown-of-thorns starfish are a major cause of loss of coral cover. One line of evidence suggests that their populations are significantly affected by the concentration of nutrients and, therefore, the amount of phytoplankton in Great Barrier Reef waters. Source: Fabricius et