SETTLEMENT STRATEGIES AND DISTRIBUTION PATTERNS OF CORAL-REEF FISHES

Patterns of habitat use established at settlement may be a primary det erminant of the distribution of coral-reef fishes within and among hab itats. However, due to the difficulty of observing fish larvae in the wild, the behaviour of individuals at settlement has rarely been obser ved. Here, we examined the behaviour at settlement of five species of damselfishes (family Pomacentridae) by conducting multi-choice experim ents in large outdoor aquaria at Lizard Island on the Great Barrier Re ef, Australia. Late-stage larvae that were competent to settle were co llected using light traps and placed in large circular aquaria at nigh t where they could choose to settle among live coral, dead branching c oral, coral rubble and bare sand habitats. We examined patterns of hab itat choice at settlement by larvae with no prior experience of the re ef (naive larvae). The effect of experience in the reef environment on habitat preferences was then determined by studying the behaviour of juveniles collected soon after settlement and exposed to the same expe rimental protocol. We also examined the importance of interspecific in teractions among late-stage larvae and interactions between newly sett led juveniles and adults in determining patterns of habitat choice exh ibited by larvae and newly settled juveniles. Late-stage larvae and ne wly settled juveniles made distinct habitat choices but the choices ma de varied widely among species. Chromis viridis (Cuvier) late-stage la rvae selected live coral and always settled as a group. Post-settlemen t C. viridis also selected live coral but exhibited stronger schooling behaviour and moved around the aquaria more frequently than late-stag e larvae. Pomacentrus moluccensis (Bleeker) consistently selected live coral and also preferentially selected habitats where conspecifics, e ither settlers or adults, were present. P. amboinensis (Bleeker) late- stage larvae preferentially selected both Live and dead standing coral habitats but avoided coral rubble. Post-settlement P. amboinensis sel ected live coral more frequently than late-stage larvae. P, coelestis (Jordan and Starks) late-stage larvae initially settled with equal fre quency among the habitats presented but exhibited an increasing use of coral rubble and dead coral throughout the day. In contrast, early po st-settlers always selected the coral rubble habitat with significantl y greater frequency than other habitats. Therefore, experience on the reef may be associated with habitat preferences in P. coelestis. P. ch rysurus settlers were distributed evenly among habitats due to agonist ic interactions among individuals observed within hours of settling. A lso, early post-settlement P. chrysurus avoided habitats containing ad ults. For the pomacentrids we tested, the patterns of habitat selectio n observed in our experiments were similar to the distribution of adul ts among habitats on the reef at Lizard Island. Also, interactions amo ng individuals at settlement could explain the spacing of individuals within habitats. Therefore, precise selection of habitats at settlemen t and behaviour among conspecifics within hours of settling may have a major influence on the distribution of coral-reef fishes within and a mong habitats. (C) 1998 Elsevier Science B.V.