Evidence of ontogenetic migration from mangroves to coral reefs by black-tail snapper Lutjanus fulvus: Stable isotope approach

Abstract

Mangroves are often considered to be important nurseries for coral reef fishes, yet this assumption has rarely been tested. At Ishigaki Island, southern Japan, black-tail snapper Lutjanus fulvus juveniles often occur in mangroves, whereas subadults and adults are usually found on coral reefs. To test the hypothesis that L. fulvus uses mangroves as a nursery, we conducted stomach content and stable isotope analyses of L. fulvus collected from mangroves and an adjacent coral reef. Stomach content analysis showed that specimens from mangroves fed on mangrove-associated prey, whereas those from the coral reef took coral reef-associated prey, indicating that the species undergoes ontogenetic changes in resource use from the mangroves to the coral reef, i.e. coral reef individuals did not migrate to the mangroves to feed. Stable isotope analysis showed that potential prey and mangrove red snapper L. argentimaculatus (control fish for mangroves) collected from the mangroves had 13C-depleted values of -23 to -17‰, distinct from the -16 to -8‰ values of potential prey and humpback red snapper L. gibbus (control fish for coral reef) collected from the coral reef. δ13C values of L. fulvus in the mangroves had a mangrove signature, whereas individuals on the coral reef gradually shifted from a mangrove signature to a coral reef signature with growth, indicating that small individuals on the coral reef were recent migrants from the mangroves. Based on the δ13C values of the subadult population of L. fulvus on the coral reef, 36 of 41 individuals were estimated to have inhabited the mangroves during their juvenile stage, demonstrating that L. fulvus used the mangroves as a nursery. © Inter-Research 2008.