Ontogenetic shift in crayfish δC as a measure of land-water ecotonal coupling.

Although ontogenetic changes in the carbon isotope ratios of marine fauna have been well studied those of freshwater organisms have not. As a result, we may have a less than adequate assessment of the incorporation of allochthonous detritus into freshwater foodwebs. This study found a δC range of 9‰ for crayfish (Orconectes virilis) from oligotrophic Canadian Shield lakes. Much (60-83%) of this variability was explained by body size. A simple isotopic mixing model suggests that by their third year of life, crayfish in these lakes rely more substantially upon terrestrial detritus than epilithic algae for energy.