Écosystèmes

Warming seas are expected to drive marine life poleward. However, few systematic observations confirm movement among entire communities at both warm and cool range edges. We analysed two continent-scale reef monitoring datasets to quantify changes in latitudinal range edges of 662 Australian shallow-water reef fishes and invertebrates over a decade punctuated by climate extremes. Temperate and tropical species both showed little net movement overall, with retreat often balancing expansion across the continent. Within regions, however, range edges shifted ~100 km per decade, on average, in the poleward or equatorward directions expected from warming or cooling. Although some species responded rapidly to temperature change, we found little evidence for mass poleward migration over the decade. Previous studies based on extreme species observations, rather than tracking all species through time, may have overestimated the prevalence, magnitude and longevity of range shifts amongst marine taxa.

A long-running coevolution experiment on bacteria and yeasts shows that adaptive evolution can shift the tipping points that trigger critical transitions in a community.

Ongoing global climate change will shift nature towards Anthropocene's unprecedented conditions by increasing average temperatures and the frequency and severity of extreme events, such as heatwaves. While such climatic changes pose an increased threat for freshwater ecosystems, other stressors like pesticides may interact with warming and lead to unpredictable effects. Studies that examine the underpinned mechanisms of multiple stressor effects are scarce and often lack environmental realism. Here, we conducted a multiple stressors experiment using outdoor freshwater mesocosms with natural assemblages of macroinvertebrates, zooplankton, phytoplankton, macrophytes, and microbes. The effects of the neonicotinoid insecticide imidacloprid (1 µg/L) were investigated in combination with three temperature scenarios representing ambient, elevated temperatures (+4 °C), and heatwaves (+0 to 8 °C), the latter two having similar energy input. We found similar imidacloprid dissipation patterns for all temperature treatments with lowest average dissipation half-lives under both warming scenarios (DT₅₀: 3 days) and highest under ambient temperatures (DT₅₀: 4 days) throughout the experiment. Amongst all communities, only the zooplankton community was significantly affected by the combined treatments. This community demonstrated low chemical sensitivity with lagged and significant negative imidacloprid effects only for cyclopoids. Heatwaves caused early and long-lasting significant effects on the zooplankton community as compared to elevated temperatures, with Polyarthra, Daphnia longispina, Lecanidae, and cyclopoids being the most negatively affected taxa, whereas Ceriodaphnia and nauplii showed positive responses to temperature. Community recovery from imidacloprid stress was slower under heatwaves, suggesting temperature-enhanced toxicity. Finally, microbial and macrofauna litter degradation were significantly enhanced by temperature, whereas the latter was also negatively affected by imidacloprid. A structural equation model depicted cascading food web effects of both stressors with stronger relationships and significant negative stressor effects at higher than at lower trophic levels. Our study highlights the threat of a series of heatwaves compared to elevated temperatures for imidacloprid-stressed freshwaters.