Acanthaster planci Linnaeus, 1758

The impact of crown-of-thorns starfish on natural coral assemblages can be severe and long-lasting. In some reefs 90% of live coral cover is lost.

Predation on corals by the crown-of-thorns starfish Acanthaster planci (Linne, 1758) has caused major damage to coral communities of the Great Barrier Reef (GBR) and elsewhere in the Indo-West Pacific region since the 1950's (Endean & Cameron 1985, Moran 1986, Moran et al. 1988, Endean & Cameron 1990). Large populations of the starfish kill entire colonies of most coral species despite individual preferences for different coral types in some circumstances (Moran 1986). The first recorded outbreaks of A. planci on the GBR occurred in the 1960's and embraced reefs in the entral third of the ecosystem (Endean 1973). Following predation of the majority of a reef's corals, most of the starfish disappeared. Within 10 to 15 yr rapidlygrowing branching and plate-like corals had reestablished an extensive coral cover on parts of many reefs (Endean & Cameron 1985). Formation of such a coral cover has been studied at several reefs of the GBR (Endean 1976) and particularly at Green Island Reef and John Brewer Reef (Pearson 1981, Done 1985, Fisk et al. 1989). Many reefs of the central GBR experienced a second outbreak during the 1980's (Endean & Cameron 1985, Moran 1986). Whether such population outbreaks of Acanthaster planci are a contemporary phenomenon or are part of an ecological pattern that has persisted for thousands of years on the GBR is a contentious issue (Moran et al. 1986, Moran & Bradbury 1989, Walbr 1980's (Endean & Cameron 1985, Moran 1986). (Cameron and Vantier, 1991)

Acanthaster predation resulted in a sharp collapse of coral populations and communities (Fisher’s p,0.05 between consecutive samplings). This decline of corals progressively affected the different reef locations, as the seastars migrated through the reef system. The coral coverage decreased gradually from values mostly above 40% in 2005 to values often below 5% in 2010, sometimes ,1% with the combined effects of the cyclone (at 12 m depth on the sites Tiahura and Vaipahu). Mass mortality of corals was accompanied by a decline in the diversity of coral assemblages, and was correlated with an increase in turf algae and dead-coral rubble and sand substrates (refer to the slopes of regressions in Figure 5, p(a),0.05). In contrast, no significant trend was observed in the cover of macro-algae, coralline algae, soft corals, or sponges (p(a).0.05). Coral genera were not equally impacted by Acanthaster predation, which resulted in a sequential extirpation of taxa from local communities. Branching and table-shaped species belonging to the genus Acropora were affected first and most heavily. Their populations declined abruptly and were extirpated from the reefs by the time coral cover fell below values of 13.7% (refer to the x-intercepts of regressions in Figure 5, arcsin(!X0) = 0.3860.03 SE). The collapse of Acropora populations was followed by those of sub-branching Pocillopora (eliminated at 1.1% coral cover, arcsin(!X0) = 0.1160.02 SE). Populations of encrusting Montipora, massive Porites, and other hard-coral assemblages also declined, showing a synchronized collapse with the entire coral communities (refer to the intercepts of regressions in Figure 5, p(b).0.05). The calcifying hydrozoan Millepora was rarely preyed upon by the seastars, and its populations did not vary with the decline in live coral. The selective predation of Acanthaster on corals, combined with the sequential time of arrival of seastars at the different reef locations and the variability in the observed peak densities, generated high spatio-temporal heterogeneity in the structure of benthic communities. Within the seven years of the Acanthaster outbreak on Moorea (2003–2010), a gradual shift of the outer-reef system was observed, from a coral-dominated one, to an ecosystem where space was mainly occupied by turf algae, coralline algae, rubble, and sand The community shift from corals to algae coincided with a shift in the composition of coral assemblages, from a state where branching genera Acropora and Pocillopora dominated in 2005, to one almost exclusively occupied by massive Porites in 2010. (Kayal et al., 2012)