Response of Chironomid Growth and Elemental Composition to Changes in Resource Stoichiometry

Aquatic macroinvertebrate diversity in freshwater systems often declines with nutrient enrichment resulting in a few tolerant taxa, such as Chironomidae midges. Chironomid dominance in enriched systems could be due to a physiological ability to allocate increased nutrients in food resources, like nitrogen and phosphorus taken up by detrital heterotrophic microbial biofilms, towards growth. Some detritivorous chironomids can increase growth rates when resource phosphorus content is elevated; however, it is unclear if all chironomid genera are able to use increased nutrients for growth. Leaves were incubated in nutrient enriched water to produce three food quality levels defined by their carbon:phosphorus ratio (C:P). Incubated leaves were then fed to different chironomid genera (Micropsectra, Chironomus). Micropsectra fed high quality (824C:P) food grew significantly more (mean±1SE, 10.77±0.50%/day) than those fed medium (1127C:P; 5.77±1.31%/day) or low quality food (1504C:P; 6.57±0.84%/day) (p=0.02). Chironomus growth did not differ significantly across food levels (p=0.63). Therefore, our preliminary data suggests that chironomid responses to nutrient enrichment may differ across genera, possibly based on differential carbon and phosphorus allocation to body tissue, causing differences in organism C:P. Generic resolution of chironomid response to basal resource enrichment can provide a framework for predicting alterations in community structure in nutrient enriched environments.