Journal of Fish Biology (2011) 78, 869–900 doi:10.1111/j.1095-8649.2011.02915.x, available online at wileyonlinelibrary.com Food partitioning and diet temporal variation in two coexisting sparids, Pagellus erythrinus and Pagellus acarne E. Fanelli*†‡, F. Badalamenti†, G. D’Anna†, C. Pipitone†, E. Riginella† and E. Azzurro§ *ICM-CSIC P.g Maritim de la Barceloneta, 37-49 – 08003 Barcelona, Spain, †CNR-IAMC Via G. da Verrazzano, 17 – 91014, Castellammare del Golfo (TP), Italy and §ISPRA Lab. of Milazzo Via dei Mille, 44 – 98057, Milazzo (ME), Italy (Received 22 September 2009, Accepted 27 December 2010) Resource partitioning in two congeneric sparids, pandora Pagellus erythrinus and axillary seabream Pagellus acarne, was investigated using stomach content analysis integrated with data on stable isotopes (δ 15 N and δ 13 C). The study was carried out on coastal muddy bottoms in the Gulf of Castellammare (southern Tyrrhenian Sea, western Mediterranean Sea) in seasons (autumn, Novem- ber 2004; winter, March 2005; spring, early June 2005), at depths between 50 and 100 m. Stomach content analysis suggested low trophic niche overlap between the two species. Pagellus erythrinus mainly preyed on strictly benthic organisms (polychaetes, brachyuran crabs and benthic crustaceans). Although it consumed benthic prey, P. acarne preferred suprabenthic prey such as peracarid crus- taceans from the benthic boundary layer a few metres above the bottom. The two species showed different isotopic values, with P. erythrinus exhibiting higher δ 15 N and more enriched δ 13 C than P. acarne, in accordance with its marked benthic behaviour and high predation on carnivore poly- chaetes. Significant temporal variability in both diet and isotopic values caused trophic differences between the two species. The autumn and winter diet differed from the spring diet and the trophic levels of both species increased from autumn and winter to spring, in accordance with variations in food availability and changes in prey δ 15 N and δ 13 C. These temporal variations may be linked to an increase in energy requirements for reproduction, together with the differing availability of preferred prey throughout the year. Significantly, lower δ 13 C was recorded in fishes collected in winter (March), suggesting the influence of river inputs as a source of particulate organic matter in this zone after the flooding season. In conclusion, these sympatric congeneric fish species displayed clear food partitioning throughout the temporal scale analysed. © 2011 The Authors Journal of Fish Biology © 2011 The Fisheries Society of the British Isles Key words: resource partitioning; stable isotopes; stomach contents; temporal variability. INTRODUCTION Resource partitioning is one of the main processes responsible for structuring pop- ulations and, consequently, communities (Gerking, 1994). Space and food are the most commonly partitioned resources among sympatric species (Schoener, 1974; Werner, 1977; Hallacher & Roberts, 1985). Habitat separation is often observed following interspecific interactions (Harmelin-Vivien et al., 1989; Golani & Galil, ‡Author to whom correspondence should be addressed. Tel.: +34 932309500; email: efanelli@icm.csic.es 869 © 2011 The Authors Journal of Fish Biology © 2011 The Fisheries Society of the British Isles