Effects of temperature on the performance of a freshwater amphipod

Temperature drives the metabolism of ectothermic organisms and impacts ecosystem functioning. Anthropogenic activities have been changing historical temperatures of freshwater ecosystems with a wide range of consequences for ecosystem processes such as leaf litter decomposition. Here we explored temperature effects on the performance of the amphipod Gammarus pseudolimnaeus, a dominant detritivore in its range. We first measured oxygen consumption under six temperatures and fitted a thermal performance curve which yielded an optimal range between 24 and 26°C. We then measured several organismal traits at four temperatures leading up to the determined optimal range. We quantified leaf litter mass loss (through feeding), somatic growth and survival under starvation at 7, 11, 17 and 23°C. Leaf litter loss was significantly lower only at the lowest temperature, with no detected differences among other treatments. Somatic growth rates increased with increasing temperature within the tested range. Organisms at warmer temperatures tended to die of starvation faster in comparison to those at colder temperatures. Our results suggest that warming may enhance leaf litter loss in certain parts of the year, but that warming could intensify organism mortality under starvation and compromise local population persistence.