Link between reproductive output and larval supply of a common damselfish species, with evidence of replenishment from outside the local population

The link between reproductive output and larval supply is described for a common damselfish species Pomacentrus vaiuli in tropical Western Australia. I monitored the reproduction of 2 groups of P. vaiuli that occupied slightly different habitats. Egg clutches laid on artificial substratum were quantified on a bi-weekly basis during the consecutive spawning seasons of 1994/95 and 1995/96. The timing of egg production was similar for both groups and showed a distinctly semi-lunar pattern. The majority of the larvae hatched during the period when flood tide occurred 2 h either side of sunset. At Ningaloo this only happens during neap tides when the tidal amplitude is at its minimum. However, this means that larvae are dispersed nocturnally when the risk of predation is minimal. No relationship was found between egg production and changes in water temperature. Spawning ended prematurely for 1 of these groups of fish following the passing of a tropical cyclone within 80 km of the coast. Larval supply of P. vaiuli was estimated in the vicinity of the reproductive sites by capturing pre-settlement fish at one of these locations (Tantabiddy), and post-settlement fish at the other (Bundegi). The arrival of P. vaiuli larvae to Tantabiddy was on a lunar cycle with periodicities between 28 to 30 d. When these larval supply data were lagged by the average pelagic duration of 22 d, and then cross-correlated with the spawning data, there was a weak relationship. At Bundegi, I constructed recruitment patterns and estimated the birth dates of juveniles, using otolith analysis. By back-calculating the birth dates of individual fish that settled at Bundegi I made 2 discoveries. Firstly, most juveniles from 1994/95 hatched when spawning output at Bundegi was low, and secondly, more than 50% of fish caught in 1995/96 hatched after the spawning season had ended prematurely. This suggests that many of the juvenile P. vaiuli that settled at Bundegi during the second summer were not produced by this population but from elsewhere. I discuss the likelihood that larvae arriving to Ningaloo are from adult populations which inhabit fringing reefs to the north and that the observed patterns in larval supply are the result of an interaction between both physical and behavioural processes.