Nemoura cinerea responses to climate change

Worldwide aquatic ecosystems are under severe pressure of climate change. Yet, studies on the effects of climate change on stream biota mainly focussed on indicator species or vulnerable species groups. The question remains, however, how more resilient species cope with elevated temperatures and drought and what the long-term consequences are for the populations of these species. The aim of the present study was therefore to determine the long-term populations responses of a common and apparently less sensitive aquatic insect to climate change-induced heat and drought and to unravel the underlying mechanisms of its persistence under such harsh conditions. To this end, the long-term population responses of the stonefly Nemoura cinerea (Plecoptera: Nemouridae) to heat and drought were assessed by linking antecedent seasonal meteorological data to 42 years of abundance data from streams in the Netherlands. The mechanisms of resilience allowing N. cinerea to cope with these stressors during the crucial transition from the juvenile to the adult stage were studied in a microcosm experiment on late-stage nymphs. Both the results of the modelling of long-term population responses to antecedent climatic variables and the observed responses in the experimental mesocosms showed that temperature, and to a lesser extent drought, had negative impacts on fitness and abundance of N. cinerea. Nonetheless, the abundance of this species still modestly increased over the last four decades. This discrepancy may be due  general improvements in water quality, an increase in intermittent sites or altered biotic interactions due to increased intermittency, reducing competition and predation of species with lower resilience. It is concluded that also species which are apparently less sensitive to the consequences of climate change do experience harmful effects, but that these appear to be outweighed by positive effects of altered biotic and abiotic conditions.