ENERGY-SOURCES AND ECOLOGICAL ROLE OF CRAYFISHES IN AN OZARK STREAM -INSIGHTS FROM STABLE ISOTOPES AND GUT ANALYSIS

Energy sources for the crayfishes Orconectes luteus and O. punctimanus in the Jacks Fork River, Missouri, were quantified using stable isoto pes (delta(13)C and delta(15)N) and gut-content analysis. A dual-isoto pe mixing model indicated that about two thirds of crayfish production originated from allochthonous carbon sources, and 30-50% of crayfish production was derived from direct consumption of animal matter. Young -of-the-year crayfishes and adult O. luteus were more carnivorous than the larger adult O. punctimanus. Contributions of energy sources dete rmined using the stable isotope mixing model were similar to results o f gut-content analysis corrected for differential assimilation of diet ary components. proportions of crayfish production attributed to anima l matter by these two methods were four to five times greater than est imates derived from uncorrected gut-content analysis. Unadjusted gut-c ontent analysis overestimated the percentage of crayfish production fr om feeding directly on detritus. Production-based calculations of cray fish food consumption rates indicated that crayfishes were the dominan t consumers of benthic invertebrates, detritus, and algae and may stro ngly influence lower trophic levels, organic matter processing, and en ergy flow in this system.