Otoliths as a tool to study reef fish population structure from coastal islands of South Brazil

To promote marine conservation and sustainable resources use it is highly important to understand reef fish population structure and dynamics. The sergeant major, Abudefduf saxatilis, is a common and abundant fish usually found in the Brazilian coasts, being considered a keystone-species for structuring benthic communities on reef habitats in the Atlantic Ocean. This study examined the morphology (shape indices and elliptic Fourier descriptors) and chemistry (Element:Ca) of A. saxatilis sagittal otoliths, collected in seven locations along the coast of South Brazil. Otolith morphology and chemistry were compared at short (range 0.5-2 km) and large (range 70-140 km) spatial scales using univariate and multivariate statistical approaches. Reclassification accuracy rates obtained from linear discrimination function analyses using both morphology and chemistry of otoliths were 61% and 82% for short and large spatial scales, respectively. No clear separation for individuals collected in islands within the Tamboretes Archipelago were observed suggesting that water masses are relatively homogeneous and/or that individuals could be highly mixed over short spatial scales. However, the higher reclassification success of the individuals belonging to Bom Abrigo, Galheta and Paz islands, indicates a limited movement of adults between habitats, a larval retention mechanism or a self-recruitment process occurring at large spatial scales.