Evidence for Habitat Residency and Isotopic Niche Partitioning in a Marine-Estuarine-Dependent Species Associated with Mangrove Habitats from the East Coast of South Africa

Abstract

Estuaries are valuable fish nurseries due, primarily, to an abundance of food and the provision of shelter in a spatially heterogeneous area. Habitats within estuaries, however, vary in their specific supply of these two factors with more structurally complex habitats tending to offer more of both food and refuge. In this study, we investigated the site residency of an abundant estuarine-dependent sparid, Rhabdosargus holubi, from two nearby but dissimilar mangrove habitats using two approaches: mark-recapture and stable isotope analysis. Results showed that rates of residency for both short- (in the order of days) and long-term (weeks) were high. Stable isotope ratios (carbon and nitrogen) were also used to compare the isotopic niche of two size groups between the two mangrove habitats. Both small and larger juveniles from a more complex creek associated with red mangroves and seagrass had a significantly broader isotopic niche width when compared with the groups from the more homogenous white mangrove habitat. R. holubi appear to establish strong residency at sites soon after recruitment which may persist until their departure from the estuary despite apparent differences in habitat quality.