Crayfish effects on fine particulate organic matter bioavailability

Background/Question/Methods

The origin and ontogeny of detritus often determines its bioavailability.  Crayfish shred and consume detrital organic matter, influencing fine particulate organic matter (FPOM) availability, composition, and quality.  Given that many invertebrates consume FPOM, crayfish can indirectly affect these organisms by altering FPOM bioavailability through organic matter fragmentation, biofilm disturbance, and defecation.  To assess crayfish effects on FPOM bioavailability, crayfish were fed sugar maple, white oak, or sycamore leaves that had been stream-conditioned for either 30-d or 150-d in hanging 1-mm mesh-bottom baskets in aquaria.  After 16 h, crayfish and remaining leaves were removed.  Crayfish feces and FPOM fragments that fell through the mesh were vacuum-filtered.  Larvae of Simulium vittatum (Simuliidae) were fed crayfish-generated FPOM or Tetramin (fish food) and growth rates were monitored.  Additionally, mortality, pupation time, emergence time and final biomass at emergence or mortality were determined. 
Results/Conclusions

C:N ratio and percent organic matter was similar across all types of crayfish-generated FPOM (i.e., 30-d conditioned sugar maple, 30-d and 150-d conditioned white oak, and 30-d and 150-d conditioned sycamore FPOM).  Tetramin had a lower C:N ratio and a higher percent organic matter than all crayfish-generated FPOM types.  S. vittatum larval size upon mortality did not differ between crayfish-generated FPOM types or Tetramin, but larva mass upon mortality was greater in Tetramin treatments.  C:N ratio was lower in sycamore 30-d  CPOM before crayfish processing.  Crayfish processing may reduce leaf-species origin and conditioning-time effects on collectors.  Overall, crayfish likely affect stream FPOM dynamics, and growth and mortality of collector invertebrates.