Effects of disturbance and consumer identity on stream ecosystem structure and function

Consumers can alter the structure and function of aquatic ecosystems, but the interactions that regulate ecosystem functioning are context dependent.  Disturbance and consumer identity can independently influence benthic ecosystem structure and function.  We determined whether consumer effects are context dependent by crossing disturbance (simulated spate) and consumer identity (crayfish, central stonerollers, or no consumers) in a factorial design in stream mesocosms.  Stream ecosystem function was quantified as leafpack decomposition and net primary productivity and ecosystem structure was measured as algal chlorophyll a and ash-free dry mass (AFDM).  Disturbance and consumer identity did not show significant interactions for any response variable.  Consumer identity but not disturbance influenced detrital breakdown as crayfish increased breakdown rates above stoneroller and no consumer treatments.  Net primary production did not differ among disturbance and consumer treatments.  Disturbance did not significantly affect chlorophyll a or AFDM abundance.  Chlorophyll a and AFDM were influenced by consumer identity as stonerollers reduced the abundance of algae and AFDM compared with crayfish and no consumer treatments.  In this experiment a simulated flood disturbance did not have strong effects on stream mesocosm properties as algal communities recovered quickly, but consumer identity influenced ecosystem responses to benthic consumers.