Publication Abstract

Spatial variation in the 15N and 13C stable isotope composition of plants, invertebrates and fishes on Mediterranean reefs: Implications for the study of trophic pathways

Spatial variation in the 15N and 13Cstable isotope composition of plants, invertebrates and fishes on Mediterranean reefs:Implications for the study of trophic pathways

S. Jennings, O. Renones, B.Morales-Nin, N.V.C. Polunin, J. Moranta, J. Coll

15N and delta 13C were determined for plants, invertebrates andfishes collected from 3 sites on the southern coast of the Mediterranean island ofMallorca, Spain. The sites were separated by distances of 1250 to 3750 m. The mean 15N ofplants was 1.1 to 4.1 ppt, benthic invertebrates 5.9 to 6.9 ppt planktonic invertebrates5.5 to 5.8 ppt, and fishes 8.4 to 13.8 ppt. 15N became enriched with increasing trophiclevel. The mean 13C of plants was -11.4 to -16.3 ppt, benthic invertebrates -14.8 to -16.8ppt, planktonic invertebrates -19.3 to -19.8 ppt and fishes -16.1 to -19.2 ppt. There weresignificant differences in the isotopic composition of individual species within theplant, invertebrate or fish groupings at each site and there were significant differencesin the isotopic composition of the same species at different sites. Depleted 13C wasassociated with benthic food chains and enriched 13C with planktonic chains. The datasuggest that benthic food chains are important to the rocky reef associated fishesstudied, as might be expected in a nutrient poor system where planktonic production isrelatively low. However, the variance in 13C composition between sites was such that therelative significance of the 2 pathways could not be determined. 15SN measurementsindicated that some of the fish species studied had adopted different feeding strategiesat different sites and, as a result, individuals of the same species could sometimes beassigned to different trophic groups at different sites. The data suggest that thesefishes exhibit plasticity in their feeding strategies and this may provide them withgreater adaptive flexibility to respond to site-specific changes in food availability.Moreover, the data provide empirical support for current theories of food web dynamicswhich suggest that trophic 'levels' are dynamic rather than fixed and that 'multichannelomnivory' is an important feature of food webs.

Reference:

S. Jennings, O. Renones, B.Morales-Nin, N.V.C. Polunin, J. Moranta, J. Coll, 1997. Spatialvariation in the 15N and 13C stable isotope composition of plants, invertebrates andfishes on Mediterranean reefs: Implications for the study of trophic pathways .MarineEcology Progress Series, 146: 109-116

S. Jennings*, O. Renones, B.Morales-Nin, N.V.C. Polunin, J. Moranta and J. Coll

Marine Ecology Progress Series, 146: 109-116