REVIEW OF THE GENETICS, DISPERSAL AND RECRUITMENT OF CROWN-OF-THORNS STARFISH (ACANTHASTER-PLANCI)

The lack of genetic structuring reported for Acanthaster planci (L.) from major biogeographical zones (i.e. Indian Ocean versus Pacific) may reflect a lack of data rather than confirmation of a recent and rapid dispersal of the species worldwide. The low level of genetic variation among A. planci populations throughout the Pacific is evidence of high levels of gene flow throughout this region. However, gene flow among widely separated reef complexes (average number of migrants per generation, N(e)m, approximately 2) is an order of magnitude less than that occurring within highly connected reef systems like the Ryukyus and the Great Barrier Reef (GBR) (N(e)m approximately 20). The genetic similarity between North-west Pacific and Australian populations is likely to reflect gene flow to each place from the central Indo-West Pacific region. Populations peripheral to the species' main distribution show greater genetic differentiation, probably as a result of founder effect. Some, like the Hawaiian and western Australian populations, show reduced genetic diversity, implying colonization by a very small number of individuals or a recent severe bottleneck in population size. Western Australian populations appear to have been derived from eastern Australian populations in the Pacific rather than Indian Ocean sources. On the GBR, genetic differentiation is low among populations that are undergoing outbreaks but there is significant differentiation among populations that are not involved in outbreaks; this suggests that a single primary source is the origin of outbreaks on the GBR. The development of distinctive DNA markers may also allow the detailed tracking of dispersal routes of A. planci and of recruitment within reefs.