Impacts of drying and crayfish invasion on stream ecosystem structure and function

Background/Question/Methods

Drought and seasonal drying can be important disturbance events in many small streams leading to intermittent or isolated habitats.  Many small streams contain crayfish populations that are often keystone or dominant species in these systems.  We conducted an experiment in stream mesocosms to examine the effects of drying and potential ecological redundancy of a native and invasive crayfish species.  We examined effects of drying (dry or wet) and crayfish presence (none, native crayfish Orconectes eupunctus or invasive crayfish Orconectes neglectus) on stream structure and function (leaf breakdown, stream metabolism, algal and insect densities) in a fully factorial design.  Each mesocosm contained a deep and shallow section and dry treatments had surface water present (10 cm depth) in deep sections where tiles and leaf packs were placed. 

Results/Conclusions

Dry and no crayfish treatments showed significantly reduced leaf breakdown than wet and crayfish treatments, respectively. However, the native and invasive crayfish species did not differ significantly in their effects on leaf breakdown. Periphyton AFDM was not affected by drying or crayfish presence. Inorganic sediment and insect density was not affected by drying, but both were significantly reduced by crayfish presence. In all cases, the native and invasive crayfish species had similar effects on ecosystem structure and function. Pools within dry portions of intermittent streams appear to function differently than pools in permanent streams. Further work is needed to determine ultimate effects of drying on trophic dynamics and ecosystem function. Given the abundance of intermittent streams and their likely increase due to global climate change, it is crucial to untangle impacts of drying.