Limnetica 32

The red swamp crayfish (Procambarus clarkii) is an invasive species in most of its current distribution range. As an omnivorous species that feeds on items of many trophic levels and is eaten by many others, it occupies a key trophic position within the invaded food webs. This trophic position, in combination with its active physiology, makes P. clarkii a suitable organism for ecotoxicological studies and, more specifically, a bioindicator of heavy metal pollution. These characteristics also make P. clarkii a likely vector of contaminants toward higher trophic levels. In this study, we (i) describe aquatic food webs in three contrasting Mediterranean wetlands in the lower Guadalquivir River Basin, southwestern Spain, each populated by invasive P. clarkii but having a different heavy metal concentration, (ii) assess the trophic role of crayfish and temporal trends in its diet using stable isotope analysis (δ¹³C and δ¹⁵N), and (iii) assess the relationship of crayfish isotopic signatures to the content of heavy metals (Cu, Zn, Pb, Cd, As) bioaccumulated in crayfish body tissues. We detected significant between-site differences in carbon and nitrogen isotopic signatures but found significant between-date differences only for nitrogen signatures. Betweensite changes in carbon and nitrogen isotopes were due primarily to variations in the relative contribution of autochthonous vs. allochthonous primary producers and shifts in crayfish abundance through time, respectively. Isotopic food web models were used to distinguish between systems driven by a detritus-based energy pathway and systems supported by detritus and primary producers. The trophic positions estimated for crayfish and other invertebrates at each site were low, suggesting the prevalence of omnivory and the occurrence of a trophic continuum rather than discrete levels. Isotopically, crayfish occupy a predator position in the observed food webs, which is consistent with the predominance of animal food sources in the species’ diet. No significant changes were found between crayfish ontogenetic stages using isotopic ratios. The site with the highest concentration of heavy metals showed the highest δ¹³C and δ¹⁵N values, and a significant correlation was found between five heavy metal elements (As, Cd, Zn. Cu, Pb) measured in crayfish and their nitrogen isotope signatures (r = 0.72, p < 0.0001), thus reinforcing its contamination biomarker role.