Habitat selection at settlement and post-settlement dynamics in juvenile fish communities in the New Caledonia lagoon

Abstract

Habitat suitability influences the growth and survival of coral reef fish juveniles, and thus the success of their recruitment in adult populations. The ultimate aim of the PhD research was to assess the relationships between the habitat characteristics in the south-west lagoon of New Caledonia at different scales, growth and abundances of juvenile fish. A photographic method was first developed in order to quantify the characteristics of coral microhabitats for juvenile fish. This method was then used for studying the relationship between microhabitat characteristics, growth trajectories back-calculated from otolith analysis, and abundances of juvenile Pomacentrus moluccensis. No significant difference was showed between the growth trajectories of individuals collected from different coral colonies. However, the density-dependent mortality of juveniles increased when the volume of holes of coral colonies decreased. At the spatial scale of two islets of the lagoon, significant spatial differences were observed in back-calculated growth trajectories, size and/or age at settlement of juveniles of Chromis viridis, Lethrinus genivittatus and Siganus fuscescens. A novel statistical procedure revealed the growth-selective mortality of juveniles C. viridis, which had a significant effect on growth trajectories. Significant differences were then showed between juvenile fish assemblages collected from artificial reefs in seaweed beds, seagrass beds and coral patches, and according to the immersion time. In the southwest lagoon of New Caledonia, changes in juvenile habitat use across seasons or during growth were showed for 53% and 39% of the observed juveniles respectively. Lastly, Generalized Linear Models allowed to explain 75% and 52% of variations in the numbers of species and individuals respectively, from a combination of environmental factors recorded at different scales. Predictions were further spatialized using a remotely sensed habitat map.