HABITAT SELECTION BEFORE SETTLEMENT BY POMACENTRUS-COELESTIS

The neon damsel, Pomacentrus coelestis, is characteristic of surge zon es on Australian coral reefs and is most abundant on outer slopes of r eefs in the southern Great Barrier Reef. When settling, it appears to 'avoid' lagoonal habitats. Recruitment records confirm that this is a general pattern regardless of whether lagoons have permanent or tempor ary connections to the ocean. This study included direct sampling, aro und One Tree Reef from the southern Great Barrier Reef, of all presett lement stages of P. coelestis with the aid of light-traps, channel net s and a plankton purse seine. Pelagic juveniles were abundant in catch es from light-traps moored outside of the reef crest. In contrast, thi s developmental stage was rare in catches from all gear types used wit hin the lagoon. The channel nets collected newly hatched larvae that e ntered the lagoon at night, but either they did not remain in the lago on or they did not survive because they were not taken from the lagoon by diurnal purse seines. This direct evidence shows that broad-scale habitat selection can begin in the planktonic stage. It implies that p elagic juveniles have excellent sensory and motor capabilities, which disqualify them from being classified and modelled as plankton. Temper ature records from inside and outside of the lagoon indicated that war m plumes (up to 3 degrees C above ambient) influence reef waters near One Tree Reef, and temperature may be one of the cues that presettleme nt fish use to identify lagoonal habitats.