Resilience and vulnerability of the stonefly Nemoura cinerea to increased temperature and drought

Aquatic ecosystems worldwide are under severe pressure from climate change. However, studies on climate change effects on stream biota mainly focus on indicator or vulnerable species, leaving unanswered how more resilient species cope with elevated temperatures and drought, and the long-term consequences for these populations. This study therefore aims to determine the long-term population responses of a common, apparently less sensitive, aquatic insect to climate change-induced heat and drought and to unravel the mechanisms underlying its persistence under such harsh conditions. The long-term population responses of the stonefly Nemoura cinerea (Plecoptera: Nemouridae) to heat and drought are assessed by linking antecedent seasonal meteorological data to 42 years of abundance data from streams in the Netherlands. The mechanisms of resilience that enable N. cinerea to withstand these stressors during its transition from juvenile to adult stages are studied in a microcosm experiment on late-stage nymphs. Results from modelling long-term population responses to antecedent climate variables and observed responses in experimental microcosms show that temperature, and to a lesser extent drought, have negative impacts on N. cinerea fitness and abundance. Nonetheless, the species’ abundance has still modestly increased over the last four decades. This discrepancy may result from general water quality improvements, an increase in intermittent sites or altered biotic interactions due to increased intermittency, reducing competition and predation by less resilient species. Thus, even species apparently less sensitive to climate change experience harmful effects, though these appear to be offset by altered biotic and abiotic conditions.