The early life history of coral trout (Plectropomus leopardus) at Green and Arlington reefs, Australia

The relative contributions of pre- and post-settlement processes to the early life history of coral trout were examined, with the aim of understanding how events occurring during the first year of life influence adult demographic parameters. Juvenile coral trout showed distinctive patterns of distribution and abundance at sites around Green Reef, which were consistent in both space (among sites) and time (between years). These patterns were influenced by substratum characteristics, with habitat associations changing as juveniles grew. Newly settled fish initially showed strong associations with low-relief, rubble-covered sand bottoms, but switched to high-relief features such as coral heads and consolidated rubble mounds after approximately two months of benthic life. Post-settlement processes (mortality and movement) for new recruits appeared to be influenced by the amount of sand-rubble habitat available; individuals occupying areas containing relatively high amounts of this substratum suffered less mortality and were more inclined to be site-attached than those from alternate habitats. Temporal patterns of recruitment were variable, but a strong settlement event coincided with the November new moon in all years of the study. Following settlement, juveniles were site-attached, and occupied home ranges that increased in area as they grew. Home ranges of the smallest recruits (25 - 60 mm SL) showed little overlap, and this pattern appeared to be facilitated by intra-specific aggression. Agonistic behaviour was rarely observed in larger recruits (61 - 102 mm), and home ranges broadly overlapped. Recruits displayed an ability to return to former locations when displaced short distances (20 m), and the distance from which juveniles could home increased with age. Recruits displayed higher site-fidelity than 1+ fish; 88% of marked 0+ individuals were resighted within 20 metres of their capture point, while only 20% of one year old fish were resighted within these areas. A change in diet occurred during early growth: diets of newly settled fish consisted mostly of epibenthic crustaceans, whereas larger juveniles (60-100 mm) were mainly piscivorous. Coral trout of all sizes consumed fish, and most piscine prey were recent recruits to the reef. Foraging modes and diurnal feeding patterns differed between size classes: larger juveniles typically fed by ambushing prey (usually small fish), whereas small recruits concentrated feeding activities around morning hours, and typically foraged by striking at invertebrates associated with rubble substrata. Diets varied spatially for large juveniles, but not for small individuals: large juveniles inhabiting structurally complex habitats (coral heads, rubble mounds) shifted to a primarily piscivorous diet sooner than those from less complex habitats. Estimates of growth rates of juvenile coral trout were influenced by larval growth histories, size-selective mortality, and variations in water temperature. Significant inter- and intra-annual differences were detected in planktonic growth rate, which were positively correlated with subsequent benthic growth. These initial patterns were accentuated by higher mortality of slow-growing juveniles, which resulted in relatively faster mean growth rates for juveniles collected later in the year. Temperature also had a strong influence on growth, and accounted for 55% of the variability in somatic growth following settlement