GENETIC-STRUCTURE OF OUTBREAKING AND NON-OUTBREAKING CROWN-OF-THORNS STARFISH (ACANTHASTER-PLANCI) POPULATIONS ON THE GREAT-BARRIER-REEF

The study used population genetic data to test whether outbreaks of crown-of-thorns starfish (Acanthaster planci) on the Great Barrier Reef (GBR) are largely derived from a single outbreak or are independent events. The consequences of different modes of outbreak for population differentiation and gene flow were predicted and then compared with those estimated from a set of 8 outbreaking and a set of 5 non-outbreaking populations sampled in 1986 and 1987. The level of inter-population variation observed among outbreaking populations was less than that among non-outbreaking populations and gene flow was greater among outbreaking than among non-outbreaking populations. Greater population differentiation among non-outbreaking than outbreaking populations was not consistent with the hypothesis that outbreaks were independent events, but was consistent with a number of outbreaks being secondary. Estimates which took account of a number of aspects of sampling error demonstrated significant levels of genetic subdivision among non-outbreaking populations but not among outbreaking populations. The lack of significant genetic subdivision of outbreaking populations, given significant levels among non-outbreaking populations, was also inconsistent with outbreaks being independent events, but was consistent with outbreaks being largely secondary. The allozyme data were insufficient to identify clearly individual populations that might have been the result of an independent outbreak. It is concluded that the majority of outbreaks are probably secondary derivatives from a single primary outbreak occurring in the northern part of the Central Section of the GBR, although the possibility that a small number of populations might outbreak independently of the main set cannot be excluded.