Feeding rates of amphipods in boreal lakes: is there a seasonal shift independent of temperature and photoperiod?

Abstract

In boreal lakes, temperature and photoperiod are important environmental cues affecting reproduction, growth and feeding rates of benthic invertebrates; however, how invertebrates cope with seasonal changes in the availability of their food sources has rarely been addressed. In this study, where temperature and light conditions were controlled, we aimed at assessing whether Hyalella azteca amphipods from the littoral zone of boreal lakes adjust their feeding rates in response to the dynamics of their food sources and their population structure. Using a gravimetric approach, we compared the ingestion and absorption rates of amphipods from a natural population collected periodically during the ice-free season. Amphipods were fed in the laboratory with conditioned leaf detritus. Feeding rates increased regardless of seasonal variations of temperature and photoperiod in the lake. Field data suggest this increase could be linked to seasonal changes in the population structure or in the diet of amphipods. This suggests that H. azteca amphipods adjusted their feeding rates with their energy and nutrient requirements and/or developed a compensatory feeding trade-off to cope with the dynamics of their different food sources in lakes.