Publication Abstract

Ontogenic shifts and spatial variation in the isotopic composition of mediterranean littoral fishes

S. Deudero, J.K. Pinnegar, N.V.C. Polunin, G. Morey and B. Morales-Nin

Stable carbon and nitrogen isotope signatures have been determined for ?littoral fishes from three localities in the Balearic Islands (NW Mediterranean) for trophic assessment. Variation in the isotopic composition was examined at multiple levels: the individual organism, individual populations (ontogenetic variation) and at area effects (different islands). Cluster analyses based on d13C and d15N resulted in two very different dendrograms for the fish assemblages from Menorca and Formentera. In both schemes, congeners of the genera Diplodus and Labrus did not cluster together, suggesting that closely related species do not necessarily feed on similar foods. Significant differences in d15N were detected between locations for S. porcus, S. scrofa and S. umbra, and significant differences in d13C were detected for S. porcus and S. scrofa. Overall there were significant spatial differences in the trophic position of littoral fishes among the 3 Balearic Islands, and fishes from Palma, Mallorca tended to feed at a higher trophic level than fishes from either Menorca and Formentera. Large-scale geographic comparisons, using earlier data from 3 sites in western Mallorca and in Corsica revealed that throughout the western Mediterranean generally, the average trophic level of fishes differs remarkably little. However, large discrepancies were observed in d15N for individual species, notably S. porcus, D. annularis, D. vulgaris and S. scriba. 13C composition of fishes did not seem to change greatly among the locations, although marked discrepancies were observed for D. puntazzo and Mullus surmuletus. Given the large-scale patterns we have observed, it is possible that the extent of multichannel omnivory which has been purported to exist in complex aquatic systems, may have been greatly overstated. Regression of d15N and d13C with fish body size revealed clear and significant trends for some species. In particular, d15N appeared to increase with body length in the macrocarnivorous fishes Scorpaena porcus, Scorpaena scrofa, Serranus scriba and Sciaena umbra. Trends were less apparent in animals which feed primarily on small benthic invertebrates, notably the four Diplodus species (D. vulgaris, D. sargus, D. annularis, D. puntazzo), and the labrids Labrus viridis and L. merula.

Reference:

S. Deudero, J.K. Pinnegar, N.V.C. Polunin, G. Morey and B. Morales-Nin (2004) Ontogenic shifts and spatial variation in the isotopic composition of mediterranean littoral fishes. Marine Biology, 145(5): 971-981