Characterizing the role of phosphorus availability and periphytic algae in the food choice and performance of detritivorous caddisflies (Trichoptera:Limnephilidae)

Organisms that rely on detritus as their primary food source may face particularly strong nutritional constraints on growth and development, given the characteristically poor quality of detrital resources. In freshwater ecosystems, the low content of P in detritus often limits detritivore growth. Additionally, a growing body of evidence suggests the biochemical composition of algae, such as essential fatty acids, can limit aquatic detritivore growth. We investigated feeding preference and growth responses of common aquatic detritivores by performing paired feeding-preference and growth experiments on 4 species of larval caddisflies (Trichoptera) from the family Limnephilidae: Asynarchus nigriculus, Anabolia bimaculata, Limnephilus externus, and Ecclisomyia sp. We manipulated both the P content and epiphytic algal biomass of a common detrital food resource (decomposing sedge [Carex sp.]) by conditioning the detritus under 2 different light (ambient, shaded) and P (ambient [low], +P) regimes. We tested 3 hypotheses that describe feeding preferences and performance under different scenarios of P limitation, algal limitation, and co-limitation by P and algae. We observed evidence of preferential feeding behavior for each of the 4 taxa, with 2 species exhibiting preferences for conditioned detritus with high algal biomass and 2 for detritus from the +P treatments. We observed agreement between feeding preferences and performance (growth, growth efficiency, mortality) for only 2 taxa, with A. nigriculus exhibiting higher growth rates and growth efficiency on their preferred high-P detritus, and L. externus experiencing lower mortality when reared on their preferred high algal biomass detritus. These findings provide an initial step toward characterizing the feeding preferences and performance responses of aquatic detritivores to 2 potentially common nutritional constraints: detrital P and algal supply.