Habitat selection before settlement by Pomacentrus coelestis

The neon damsel, Pomacentrus coelestis, is characteristic of surge zones on Australian coral reefs and is most abundant on outer slopes of reefs 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 temporary connections to the ocean. This study included direct sampling, around One Tree Reef from the southern Great Barrier Reef, of all presettlement stages of P. coelestis with the aid of light-traps, channel nets and a plankton purse seine. Pelagic juveniles were abundant in catches from light-traps moored outside of the reef crest. In contrast, this developmental stage was rare in catches from all gear types used within the lagoon. The channel nets collected newly hatched larvae that entered the lagoon at night, but either they did not remain in the lagoon 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 pelagic juveniles have excellent sensory and motor capabilities, which disqualify them from being classified and modelled as plankton. Temperature records from inside and outside of the lagoon indicated that warm plumes (up to 3 degrees C above ambient) influence reef waters near One Tree Reef, and temperature may be one of the cues that presettlement fish use to identify lagoonal habitats.