Use of 13C/12C to trace dissolved and particulate organic matter utilization by populations of an aquatic invertebrate.

The 13C/12C of limnephilid caddisfly larvae (Clistoronia magnifica) grown in the presence of red alder leaf particulate organic matter (POM) and alder leaf leachate was found to be identical to the 13C/12C of larvae grown on alder POM, but with isotopically contrasting grass leachate substituted for the above alder leachate. The isotopic similarity between these insects and the alder POM common in both treatments indicates that grass leachate was not a source of insect carbon. In contrast to these results, the 13C/12C of larvae grown on grass POM and leachate was markedly different from the 13C/12C of larvae raised on grass POM and alder leachate. The relative 13C depletion found in larvae from the latter treatment could be accounted for only if a significant amount of carbon derived from alder leachate had been incorporated into insect biomass. Significant differences in yield of insect biomass among the above treatments also were found.