ALLOZYME ELECTROPHORESIS DEMONSTRATES THAT THE SCLERACTINIAN CORAL MONTIPORA-DIGITATA IS 2 SPECIES

Allozyme electrophoresis at five loci was used to clarify the species status of two morphs of the scleractinian coral Montipora digitata (Da na, 1846), using specimens collected from three locations off the Quee nsland coast between October 1991 and April 1993. The two morphs, occu rring sympatrically, were distinguished by one fixed gene difference a t Locus LT-2 and frequency differences at three other loci, indicating reproductive isolation between them. Populations of both morphs were generally in Hardy-Weinberg equilibrium, suggesting that sexual reprod uction does occur. Despite sampling designed to reduce the chance of c ollecting clone-mates, the genetic diversity ratio (G(o):G(e)) indicat ed that asexual reproduction also occurs. This is in agreement with th e known modes of reproduction for this species. There was significant genetic differentiation between populations of one of the morphs of M. digitata. This could have been influenced by greater degrees of asexu al reproduction in this morph, selection within sites, or variation in larval survival and recruitment patterns. Relatively low F-st (differ entiation among populations) values found for a broadcast spawning spe cies during this study are in accordance with the hypothesis that broo ded planulae are adapted for rapid settlement, whereas planulae produc ed by broadcast spawners are adapted for widespread dispersal.