Unexpected patterns of chironomid larval size in an extreme environment: a highly glaciated, alpine stream (pdf)

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Unexpected patterns of chironomid larval size in an extreme environment: a highly glaciated, alpine stream

Hydrobiologia https://doi.org/10.1007/s10750-018-3579-y PRIMARY RESEARCH PAPER Unexpected patterns of chironomid larval size in an extreme environment: a highly glaciated, alpine stream Stefan Andreas Schütz . Leopold Füreder Received: 5 October 2017 / Revised: 22 February 2018 / Accepted: 3 March 2018 Ó The Author(s) 2018 Abstract In this article, we report on the development and growth of alpine chironomid species in a highly glaciated headwater, using biometrical analyses. Glacially influenced alpine streams are characterized by year-round harsh environmental conditions. Only a few, highly adapted benthic insects, mainly chironomid larvae (genus Diamesa) live in these extreme conditions. Although several studies have shown patterns in ecosystem structure and function in alpine streams, cause–effect relationships of abiotic components on aquatic insects’ life strategies are still unknown. Sampling was performed at Schlatenbach, a river draining the Schlatenkees (Hohe Tauern NP, Austria), at three sites and on six occasions from August to October 2015. Semi-quantitatively sampled Diamesa cinerella (Meigen 1835) and Diamesa steinboecki (Goetghebuer 1933) larvae were biometrically analysed, and they showed differences in larval size and biovolume with higher values close to the glacier. Handling editor: Eric Larson Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10750-018-3579-y) contains supplementary material, which is available to authorized users. S. A. Schütz (&) L. Füreder River and Conservation Research, Institute of Ecology, Leopold-Franzens University of Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria e-mail: Considering the decreasing water temperatures but increasing benthic organic matter towards the glacier, food availability seems to play a crucial role for larval size in highly glaciated alpine headwaters. This is the first study to show that harsh conditions in these environments (low temperatures, high turbidity and flow dynamics) may exclude many taxa, but favour other, highly adapted species, when their essential needs (food quality and quantity) are guaranteed. Keywords Life cycle Diamesa Biometric analyses Glacier retreat Chironomidae Introduction Habitats with harsh environmental conditions are spread all over the world ranging from hot springs, dry desserts to high altitude mountaintops (Füreder, 1999; Jacobsen & Dangles, 2012). Streams in the alpine zone are among the most extreme freshwater ecosystems, characterized by harsh environmental conditions like high solar radiation, year-round low air and water temperatures, scarce vegetation, short snow free season and often draining glaciers in the catchments (Milner & Petts, 1994; Ward, 1994; LodsCrozet et al., 2001; Füreder et al., 2005; Brown et al., 2015). In the future, climate change effects intensify the already rough abiotic conditions by accelerated 123 Hydrobiologia glacier melt, leading to enhanced discharge with lower water temperatures, increased turbidity, higher abrasion, lower habitat stability, little algal growth, and hence decreased nutrient retention compared to the current situation (Brown et al., 2007, 2010; Finn et al., 2010; Robinson et al., 2014). Glacier recession will also create new ice-free habitats in glacier-fed (kryal, sensu Steffan, 1971) streams (Robinson et al., 2014), representing a refuge for alpine benthic invertebrates in times of climate change (Brittain & Milner, 2001; Finn et al., 2010). The larval community of these aquatic insects, dominated by chironomids (Steffan, 1971), has to face and master the stressful living conditions in order to successfully colonize and inhabit the uppermost stream reaches of alpine rivers. Former studies pointed out that highly adapted species, mainly from the chironomid genus Diamesa (Milner & Petts, 1994; Brittain et al., 2001; Robinson et al., 2001) withstand the tough abiotic conditions and inhabit kryal streams directly from the glacier snout, partially reaching high individual numbers at suited microhabitats (Finn et al., 2010; Robinson et al., 2014; Rossaro et al., 2016). Recently, significant knowledge concerning species habitat preferences and harshness resistance has been gained (e.g., Niedrist & Füreder, 2016), identifying water temperature and nutrient availability as the major driving forces for species appearance and benthic community composition (e.g., Milner & Petts, 1994; Brittain et al., 2001; Finn et al., 2010; Marziali & Rossaro, 2013). Chironomids are holometabolic insects following a defined life cycle pattern. The larva is hatching from the egg, goes through four larval instars (L1, L2, L3 and L4) to a pupa stage, and finally emerges as an adult, terrestrial insect (Walker, 1987). Despite this relatively simple development, chironomid growth and life cycles in the colder climatic zones have hardly been investigated (but see Nolte & Hoffmann, 1992; Hannesdottir et al., 2012). This is particularly true for high alpine species. Most studies so far concentrated on the benthic larval life of Ephemeroptera, Plecoptera and Trichoptera (e.g., Brittain, 1983; Dobrin & Gibberson, 2003; Finn & Poff, 2008; Resh & Rosenberg, 2010; Beracko et al., 2016; Carlos & Puliafico, 2016). Some of these former studies revealed correlations of changing environmental conditions and the benthic larval growth in temperate streams below the tree line. 123 In other studies, water temperature and/or nutrient availability seemed to be the main driving forces shifting benthic larval life (Erba et al., 2003; Reynolds & Benke, 2005; Sand & Brittain, 2009). Quite a number of surveys in the past were set up as laboratory experiments to manipulate the most important abiotic factors and strictly follow the nymphal reactions on the altered environmental conditions (e.g., Mackey, 1977; Sweeney et al., 1986; Corkum & Hanes, 1991; Stanko-Mishic et al., 1999; Hooper et al., 2003). Thereby, increased water temperature or nutrient availability, compared to the control conditions, partially led to improved larval growth and increased biovolume (e.g., Sweeney et al., 1986; Reynolds & Benke, 2005; Wagner, 2005). These laboratory experiments were a crucial step to understand the principal mechanisms of benthic larval growth and development in temperate and low alpine streams. By simulating changing environmental conditions on the benthic larval life, relevant interactions of the naturally predominant abiotic conditions might be missed, leading to misinterpretations of current processes, future changes and adaptions of benthic species to changing environmental conditions (Sweeney et al., 1986). Moreover, the complex and harsh abiotic characteristics of a highly glaciated stream are hardly reproducible in laboratory experiments. Therefore, knowledge about the larval growth dynamics, development histories, age structure, retention time and colonization patterns of the ben (...truncated)