Detecting age-structured effects in growth performance of coral reef fish juveniles

Abstract

The growth performance of coral reef fish juveniles collected in different habitats is often used as a proxy for habitat quality for juveniles. However, back-calculated growth trajectories of juveniles may be age-structured, for instance, because of potential differences in initial offspring size and/or quality or size-selective mortality. A novel approach is proposed to isolate growth performance of coral reef fish juveniles from potential age-based factors. Juveniles of Chromis viridis (Pomacentridae), Lethrinus genivittatus (Lethrinidae) and Siganus fuscescens (Siganidae) were collected from waters around inshore and offshore islets in a coral reef lagoon. Individual growth trajectories were back-calculated from otolith increments and compared with repeated-measures generalised linear models (RM-GLMs). Settlement marks in otoliths were used to differentiate larval and juvenile growth trajectories for each individual. For the 3 species, fish from around the offshore islet presented significantly larger size-at-age during their larval stage than those from from around the inshore islet. Juveniles of L. genivittatus and S. fuscescens from around the offshore islet remained larger than inshore juveniles at the same age, while growth curves of C. viridis from the 2 islets crossed at settlement so that inshore fish were larger as juveniles than offshore individuals. RM-GLMs revealed that the growth trajectory was significantly age-structured for C. viridis only. These results suggest that post-settlement age may be used as a covariate in comparative analyses of larval growth in order to isolate growth performance from potential age-based factors. © Inter-Research 2009.