Stable carbon and nitrogen ratios in the sand smelt from a Mediterranean coastal area: feeding habits and effect of season and size

Enriched delta(13)C values (annual average -11.2parts per thousand) suggest that in the study site (Stagnone di Marsala, Italy) the sand smelt Atherina boyeri exploited benthic prey throughout the year. In particular, Mysidacea and Isopoda seemed to dominate the diet. Stomach content data from the literature was in partial agreement with the present isotopic analysis suggesting that, while Mysidacea and Isopoda are exploited by A. boyeri, Copepoda Harpacticoida and Amphipoda are the dominant food items of the sand smelt diet. Several hypotheses are proposed to explain such partially different results from the two techniques. Both season and size influenced the delta(13)C and delta(15)N values of A. boyeri. Although throughout the sampling year, A. boyeri showed very enriched delta(13)C and delta(15)N values consistent with a diet based on benthic resources, it showed significant seasonal differences in both nitrogen and carbon isotope ratios. Such a finding suggests that the food preferences of A. boyeri undergo small seasonal differences, probably as a consequence of prey availability. Size also affected the isotopic composition of the sand-smelt indicating that this species shows ontogenetic diet shifts in the study site. Compared with other Mediterranean trophic data of the sand smelt these results substantiate the great adaptability of A. boyeri to the local environmental resources and its trophic plasticity. (C) 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved.