Variable larval growth in a coral reef fish

Understanding the functional linkages between the pelagic and demersal stages of marine organisms is a central goal in ecology. To better understand events that occurred during the larval period as well as their initial influence on juvenile traits, we examined individual level variation in early life-history traits (larval and early juvenile otolith growth rates, size-at-age, and larval duration) of 3 seasonal cohorts of the common coral reef fish Thalassoma bifasciatum (Bloch) (Labridae). Juveniles were collected at regular intervals (every second day) for 2 wk following their first appearance on the nearshore reefs of Barbados, West Indies. Otolith analysis indicated that each cohort exhibited a broad range of larval traits. Individuals with shorter larval durations had faster otolith growth and settled at relatively smaller sizes (based on otolith length and standard length) than larvae with longer larval durations, which exhibited slower otolith growth rates. Despite the range in larval durations for T. bifasciatum, otolith growth records revealed no evidence for delay of metamorphosis. Instead, the range in larval durations is likely to be the result of a variable pelagic environment influencing growth rates. Because metamorphosis in this species is an energetically costly non-feeding (3 to 5 d) period, we propose that successful metamorphosis requires a minimum energy reserve. Slower growers may need to remain in the plankton longer (consequently attaining larger sizes) to obtain this minimum condition. Variability in early life-history traits also occurred among the seasonal cohorts. Despite differences in patterns of larval otolith growth, mean larval duration was similar for the 2 fall cohorts (57 and 55 d), but much shorter for the spring cohort (42 d). Such inter-cohort variability in early life-history traits suggests a variable pelagic environment. In contrast to the larval period, juvenile growth rates were much less variable within and among cohorts, reflecting a more constant physical and biological environment on the reef.