Phenotypic variation across populations of red mullet (Mullus barbatus) in different environments of the central Mediterranean

Abstract

Geometric morphometrics is an effective tool for quantifying intraspecific variations in fish body shape and differentiating populations and fisheries stocks. This study used geometric morphometrics to examine patterns of intraspecific morphological differentiation among four red mullet (Mullus barbatus) populations in the Strait of Sicily in the central Mediterranean Sea. We hypothesised that morphological differences among local populations were caused by the diverse hydrodynamic features characterising the sampled areas and maintained by geographical isolation. We also examined whether body shape homogeneity or variability within local populations was related to seabed rugosity as an indicator of habitat complexity. We found that the morphological divergence between local populations was constrained by geographical proximity. Populations varied primarily in body depth, with more elongate specimens inhabiting hydrodynamic areas. In addition, site-specific homogeneity in body shape was positively related to seabed rugosity, so that in more structurally complex habitats body shape was less morphologically variable. An improved understanding of the spatial structure of red mullet populations in the Strait of Sicily is needed to better define the boundaries of natural populations.