Environmental Biology of Fishes 59: 191–198, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. Intralocality variation in feeding biomechanics and prey use in Archosargus probatocephalus (Teleostei, Sparidae), with implications for the ecomorphology of fishes Michele M. Cutwa & Ralph G. Turingan a Department of Biological Sciences, Florida Institute of Technology 150 West University Boulevard, Melbourne, FL 32901, U.S.A. (e-mail: turingan@fit.edu) a Corresponding author Received 18 March 1999 Accepted 8 May 2000 Key words: functionalmorphology, habitat heterogeneity, phenotypic plasticity, estuary, durophagy, intraspecific, fish Synopsis Archosargus probatocephalus in a Florida estuary was investigated to explore intraspecific variation in prey utiliza- tion and jaw biomechanics. Volumetric contribution of major prey types and seven biomechanical features of the oral jaws that characterize prey-capture and processing performance were contrasted between two locations within the estuary. At Mosquito Lagoon, where A. probatocephalus inhabited mostly oyster beds, mangroves and salt marshes, fish consumed mostly thick-shelled bivalves, gastropods, crabs, and tubiculous polychaetes and amphipods. In con- trast, conspecifics at Indian River Lagoon that inhabited mostly seagrass beds and algal turf consumed predominantly algae, seagrass, epiphytic invertebrates and small bivalves and gastropods. Difference in magnitude of durophagy between locations was associated with differences in oral-jaw biomechanics. Analyses of covariance indicated that A. probatocephalus at Mosquito Lagoon had more massive jaw muscles and bones, than conspecifics at Indian River Lagoon. Variations in lever ratios for jaw-opening and jaw-closing between locations were not significant. It is hypothesized that intralocality differences in food habits have induced the development of feeding morphologies that enhance the ability of A. probatocephalus to successfully exploit locally dominant prey resources within the estuary. Plasticity of the feeding mechanism of A. probatocephalus may buffer the species from the adverse effects of settling on heterogeneous habitats that contain variable prey resources such as those found within estuaries. Introduction The central theme of ecological and evolutionary stud- ies of species that occupy broad geographic areas is understanding how a species adapts to variable environ- mental conditions within its distribution. The ability of a species to successfully occupy heterogeneous habi- tats may depend on its ability to respond to local envi- ronmental conditions, either through local adaptation or alteration of phenotypic developmental pathways in response to environmental stimuli (i.e., pheno- typic plasticity) (Wright 1931, Via & Lande 1985, Schlichting & Pigliucci 1998). Our lack of under- standing of the adaptive role of phenotypic plasticity (Stearns 1989, Scheiner 1993, Travis 1994) has under- scored the need for studies that address the relation- ship between resource exploitation and morphology within conspecifics that inhabit different environments (e.g., Williams & Moore 1989, Wainwright et al. 1991). Many studies have shown that morphology and food habits vary among conspecific fishes that occupy different habitats (Lindsey 1981, Lavin & McPhail 1986, Skulason et al. 1989, Ehlinger 1990, Meyer 1990, Mittelbach et al. 1992, Turingan et al. 1995).