Microbial community structure and function in response to larval chironomid feeding pressure in a microcosm experiment

Studies concerning the interactions between macroinvertebrate and microbial communities have been carried out for some time. However, most of these st udies have been simple feeding relationships that as a group have produced ambiguous results. We perceive these relationships to be more complex, enco mpassing not only microbial population density but also structure and funct ion. To further understand these relationships, we employed molecular and b iochemical techniques to study microbial structural and functional diversit y in relation to macrobenthic feeding pressure. We studied the effect of fe eding by the three population densities of larval midge, Chironomus tentans , (Diptera: Chironomidae) on microbial community organization. No significa nt difference in microbial biomass carbon (10.0 mg/g DWS +/-1.97) was seen between the three treatments. However, we did detect significant shifts in microbial structure and function with increases in midge population density . The activities of carbon (C) and nitrogen (N) acquiring enzymes were nega tively correlated with midge population density. While the C:N ratio was po sitively correlated with midge population density, suggesting that while th e concentration of nitrogen decreased, its availability to the chironomids increased. There was also a marked difference in microbial community struct ure with increasing midge population density. These shifts in microbial org anization are indicative of a complex set of interactions between the micro bial community and the chironomid larvae.