Increased chironomid growth with increasing food quality

Background/Question/Methods

Aquatic macroinvertebrate diversity often declines with nutrient enrichment and results in a few tolerant taxa remaining. Chironomidae midges are common dominant taxa in enriched freshwaters. Chironomid dominance in nutrient enriched systems could be due to allocation of extra nutrients, such as nitrogen and phosphorus, towards growth. Heterotrophic biofilms associated with organic matter can assimilate extra nutrients in the water column that increase biofilm biomass and production and increase the amount of nitrogen and phosphorus relative to carbon. Assemblages of non-predaceous chironomids have been shown to increase growth rates when phosphorus content in basal food resources is elevated; however, it is unclear if all Chironomidae genera are able to use increased nutrients. We fed a chironomid genus, Micropsectra,leaves incubated in water enriched with combinations of two levels of nitrogen (low and elevated; 11 and 1109ug/L, respectively) and phosphorus (low and elevated; 1 and 109ug/L, respectively).

Results/Conclusions

Micropsectra fed leaves incubated under elevated nitrogen and phosphorus concentrations grew significantly more (mean±1SE, 1±0.15mm) than those fed leaves incubated with low nitrogen and phosphorus  (0.44±0.19mm), elevated nitrogen  (0.30±0.15mm), or low nitrogen (0.18±0.15mm) (p=0.0001). Our preliminary data suggests that some genera are able to use excess nutrients for growth. Generic resolution of chironomid response to basal resource enrichment can provide a framework for predicting alterations in community structure in nutrient enriched environments.