Ontogenetic habitat utilization patterns of juvenile reef fish in low-predation habitats

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Food and predation are considered to represent the main factors affecting habitat selection by juvenile reef fish. Generally, coral reefs shelter more invertebrate prey but also harbor more predators compared to vegetated areas. To avoid predation, many juvenile fish may select lower-risk vegetated areas rather than coral reefs. Very little information is known about habitat selection by juvenile fish if coral reefs have similar predation rates as vegetated areas. In this study, we quantified the density, diet, survival rate, and food availability of four reef fish species (Lethrinus harak, L. obsoletus, Lutjanus gibbus, and Parupeneus indicus) as well as predator and competitor density within a low-predation lagoon containing bare sand, coral reefs, and seagrass beds. The results showed that the two lethrinids used seagrass beds as primary habitats as small juveniles. Large juveniles of L. obsoletus (5 cm total length after dietary shift) and most juvenile L. gibbus preferred coral reefs. P. indicus were dietary generalists in most habitats. Overall, these instances of ontogenetic habitat selection may be related to variations in diet in each species. We also found that predation rates were extremely low (<30 %) in both coral and seagrass habitats and that coral reefs sheltered higher invertebrate prey densities (80 ind m−2) than did seagrass beds (30 ind m−2) and bare sand (<10 ind m−2). We hypothesized that competition is a factor potentially affecting habitat selection by juvenile reef fish, as more competitor fish inhabited coral reefs. Fish optimize the advantages of particular habitats for growth and for avoiding competition by selecting ideal habitats under conditions of low predation.