Structural and functional changes in the macroinvertebrate community in Alpine stream networks fed by shrinking glaciers

Abstract

The status of glaciers is alarming globally with still unknown effects on freshwater ecosystems. Thegeneral aim of this study was to investigate the structural and functional changes in the macroinvertebrate communityin stream networks fed by shrinking glaciers in relation to environmental variables. Feeding glaciers haddifferent surface areas and retreating rates. We selected 10 study sites in the Italian Alps, spanning five kryal, twoglacio-rhithral, two krenal and one proglacial pond, sampled twice in summer 2018. Eight of these sites weresampled previously between 1996 and 2014. In all, in 2018, > 15,000 individuals (73 taxa) were collected, of which82 % were chironomids (Diptera Chironomidae) (33 taxa). Diamesa zernyi gr. (Chironomidae Diamesinae) wasthe most frequent and abundant taxon, followed by Oligochaeta and Chironomidae Orthocladiinae. Taxonomical(Shannon index) and functional (based on functional feeding groups) diversity both increased with decreasingglacial influence (estimated as glacial index, GI, based on distance from the glacier snout of each site and glacierarea), from kryal to glacio-rhithral and krenal habitats. Taxa distribution was explained mainly by GI, maximumwater temperature, substrate stability, silica, epilithic chlorophyll-a, and benthic particulate organic matter. Thesame variables explained temporal differences in the community structure for the eight sites re-sampled in the lasttwo decades. Among the taxa best associated with high GI was the chironomid Diamesa steinboecki, that in 2018was exclusive of the kryal sites with GCC (% glacier cover in the catchment, expressed in a range from 0 %–100 %)> 50 % and maximum temperature < 5 °C. This species was absent only in the kryal site C0 (GCC = 33 %), whereit was dominant in 1996 –1997. This site was still fed by ice melt in 2018, but resembled a glacio-rhithral site inhabitat features (e.g. maximum temperature > 6 °C) and biota (e.g. % Diamesa spp. < 30 %). In C0, it was evidentthat in the last 22 years, the macroinvertebrate community changed remarkably. This change was due to upstreammigration of generalist insect species to sites once exclusive for kryal species with consequent changes in food webstructure and loss of strictly kryal species, first D. steinboecki that we propose as the “flagship” species of the kryalin the Alps. The site C0 represents a “tipping point”, showing us the effects of climate change on alpine biodiversityin a relatively short period; unfortunately, there are many such sites in the Italian Alps.

Congruence between molecular and morphological systematics of Alpine non‐biting midges (Chironomidae, Diamesinae)

“…Within this scenario, Diamesa species are seriously threatened by extinction in concomitance with the disappearance of the kryal habitat, leading to the decrease of regional biodiversity (Jacobsen et al., 2012). Among the Diamesa species most sensitive to climate change and hypothesized to disappear in the Alps ( D. steinboecki , D. goetghebueri, and D. zernyi ) (Lencioni, 2018), the “glacier fly” D. steinboecki (Serra‐Tosio, 1974) is the species most likely to disappear first (Lencioni et al., 2021). These findings make D. steinboecki the best indicator of high glacial level in the Southern Alps: the “flagship” species of the Alpine kryal.…”

“…The reasons for its disappearance are yet to be fully understood. It was suggested that its strong cold stenothermy and cold hardiness could prevent it from adapting to water only 2–4 degrees warmer than its thermal optimum (2°C) (Lencioni et al., 2021). Also, competition for food and space with newly colonizing species and predator range shifts can negatively impact on D. steinboecki (Khamis et al.…”

Research advances emerging from SEFS11: The 11th Symposium for European Freshwater Sciences

“…Contributions to this Special Issue highlight the vibrancy of research activity within freshwater sciences across and beyond Europe. Much of the research presented focuses on freshwaters of conservation interest, from those within protected national parks (Buj et al 2020;Ivić et al 2020;Vurnek et al 2020) to those in vulnerable areas of the Alpine region (Carosi et al 2020;Lencioni et al 2020). As European freshwaters continue to respond to climate change and other anthropogenic pressures, such research will underpin effective monitoring and management strategies that support biodiversity within functional ecosystems (Markovic et al 2017).…”

“…Notable changes in community composition over the 22-year study period reflected the loss of strict kryal species such as the chironomid Diamesa steinboecki (Diptera: Chironomidae) and upstream migration of generalist insects, with consequent changes in food web structure. Lencioni et al (2020) thus suggest D. steinboecki as a 'flagship' species of kryal Alpine streams: a species that may be lost as sites pass 'tipping points' in response to rapid global warming.…”

“…These papers have common strengths including the analysis of long-term data to support conservation and management strategies in changing European climates (Carosi et al 2020;Maximov et al 2020;Vurnek et al 2020), and use of both traditional and genetic identification methods to characterize biodiversity -again supporting species conservation, in particular within the protected waters of the SEFS11 host nation, Croatia (Buj et al 2020;Ivić et al 2020;Piria et al 2020). Other studies bring new insight into structural and functional invertebrate responses to disturbance (Lencioni et al 2020;Šumanović et al 2020), andZandonà et al (2020) are unique in exploring the stoichiometry of nutrient excretion by consumers with contrasting diets and body elemental composition. Below we briefly summarize each of these papers, which collectively make a significant contribution to freshwater science.…”