Coastal Sciences, Gulf Coast Research Laboratory
Stable isotope (SI) values of carbon (delta C-13) and nitrogen (delta N-15) are useful for determining the trophic connectivity between species within an ecosystem, but interpretation of these data involves important assumptions about sources of intrapopulation variability. We compared intrapopulation variability in delta C-13 and delta N-15 for an estuarine omnivore, Spotted Seatrout (Cynoscion nebulosus), to test assumptions and assess the utility of SI analysis for delineation of the connectivity of this species with other species in estuarine food webs. Both delta C-13 and delta N-15 values showed patterns of enrichment in fish caught from coastal to offshore sites and as a function of fish size. Results for delta C-13 were consistent in liver and muscle tissue, but liver delta N-15 showed a negative bias when compared with muscle that increased with absolute delta N-15 value. Natural variability in both isotopes was 5-10 times higher than that observed in laboratory populations, indicating that environmentally driven intrapopulation variability is detectable particularly after individual bias is removed through sample pooling. These results corroborate the utility of SI analysis for examination of the position of Spotted Seatrout in an estuarine food web. On the basis of these results, we conclude that interpretation of SI data in fishes should account for measurable and ecologically relevant intrapopulation variability for each species and system on a case by case basis.
Fulford, R. S.,
(2013). Quantifying Intrapopulation Variability in Stable Isotope Data for Spotted Seatrout (Cynoscion nebulosus). Fishery Bulletin, 111(2), 111-121.
Available at: http://aquila.usm.edu/fac_pubs/7774