Ontogenic shift in critical fluid flow threshold and habitat use by the caddisfly Dicosmoecus gilvipes, and implications for ecosystem processes

Mike Limm
NCED Postdoctoral Associate
St. Anthony Falls Laboratory

ABSTRACT

Disturbance by flooding can dramatically disrupt population and community structure in stream ecosystems. If strongly interacting species are affected, energy and nutrient dynamics may be altered. In a Northern California stream we quantify the impact of the limnephilid caddisfly Dicosmoecus gilvipes on periphyton structure and ecosystem processes, quantify how Dicosmoecus vulnerability to disturbance can vary with ontogeny, and investigate how their case design influences fluid flow resistance.

Dicosmoecus larvae reduced periphyton accrual, gross primary productivity, and ammonium uptake, and their impact persisted 46 days after the larvae were removed. Critical fluid flow threshold (sufficient to dislodge larvae from substrates) increased with larval size, as did larval flow velocity preference. The lateral extensions Dicosmoecus build on their case provided stability against overturning in fast flow and may improve their ability to forage efficiently in turbulent flow conditions. Our results suggest any change in flood timing, frequency, and/or magnitude due to river regulation or climate conditions may impact Dicosmoecus populations and alter ecosystem processes in Northern California streams.