Climate change modifies the size structure of assemblages of emerging aquatic insects

Abstract

Summary Climate change is expected to not only raise water temperatures, but also to cause brownification of aquatic ecosystems via increased inputs of terrestrial dissolved organic matter. While efforts have been made to understand how increased temperature and brownification separately influence aquatic food webs, their interactive effects have been less investigated. Further, although climate change effects on aquatic ecosystems likely will propagate to terrestrial consumers via changes in aquatic insect emergence, this has rarely been studied. We investigated the effect of climate change on aquatic insect emergence, in a large‐scale outdoor pond facility where 16 sections – each containing natural food webs including a fish top‐consumer population – were subjected to warming (3 °C above ambient temperatures) and/or brownification (by adding naturally humic stream water). Aquatic insect emergence was measured biweekly over 18 weeks. We found no effect of warming or brownification on total emergent insect dry mass. However, warming significantly reduced the number of emergent Chironomidae, while numbers of larger taxa, Trichoptera and Ephemeroptera, remained unchanged. On average, 57% and 58% fewer Chironomidae emerged from the warmed clear and humic pond sections, respectively. This substantial decrease in emergent Chironomidae resulted in a changed community structure and on average larger individuals emerging from warm sections as well as from humic sections under ambient conditions. There was also a weak influence of fish biomass on the size structure of emergent aquatic insects, with a positive relationship between individual insect size and total fish biomass, but effects of fish were clearly subordinate to those of warming. Climate change impacts on aquatic systems can have widespread consequences also for terrestrial systems, as aquatic insects are ubiquitous and their emergence represents an important resource flow from aquatic to terrestrial environments. While we found that neither warming nor brownification quantitatively changed total aquatic insect emergence biomass, the warming‐induced decrease in number of emergent Chironomidae and the subsequent increase in average body size will likely impact terrestrial consumers relying on emergent aquatic insect as prey.

Food web structure shaped by habitat size and climate across a latitudinal gradient

“…, Jonsson et al. , Lefort et al. ), our results slightly differ from those manipulating temperature.…”

“…Moreover, climatic instability and extremes can decrease insect population sizes and delay insect development and survivorship (Jonsson et al. ), thus decreasing biomass turnovers in these harsh ecosystems.…”

“…, Jonsson et al. ). Indeed, it is known that top predators require more stable climatic conditions than their prey (e.g., Daufresne et al.…”

Importance of Riparian Zone: Effects of Resource Availability at Land-water Interface

“…terrestrial insects, leaf litters, aquatic emerging insects, salmon carcasses), and they are usually beneficial to both sides, with elevated population size, higher growth rate, and larger body size. However, ecosystems around the world are increasingly impacted by human landscape disturbances, such as land use, climate change and invasive species, so that cross-ecosystem subsidies should be impacted by these changes [119,127]. Understanding how ecological and physical processes of resource subsidies respond to these changes needs interdisciplinary research approaches, including ecohydrology and ecogeomorphlogy [185], as well as ecological stoichiometry [186] and community and ecosystem genetics [187,188].…”

“…an increase of 3°C above ambient temperature caused an average of 57-58% fewer emerging Chironomidae. However, total aquatic insect emergence biomass was not influenced by warming, and thus caused an average larger individuals emerging from warm waterbodies [127]. Conversely, another study showed that only the emerging Chironomidae adults were larger with raised temperature, while the emergence of both medium and large-sized insects were decreased, moreover, rising temperature decreased time to emergence [128].…”