engleski

Stable isotopes as proxies for food sourcing in alpine streams undergoing glacial recession

Because of contemporary global warming and glacier shrinkage, alpine streams have received increased attention as sensitive indicators to climatic change. The ecological functional characteristics (e.g., food sourcing and consumption) of alpine streams are vastly influenced not only by thermal and hydrological regimes, but also by structure and activity of benthic communities (i.e., macroinvertebrate fauna), and inputs of primary food sources (i.e., autochthonous and allochthonous organic matter) within streams. In this talk, I highlight the use of carbon and nitrogen stable isotope methods in tracing food source changes and feeding plasticity of macroinvertebrates within alpine streams undergoing rapid glacial recession. Our goals were to investigate the response of macroinvertebrate assemblages to changes in food resources regarding: 1) the glacial recession, 2) differences among various alpine stream types that display contrasting riparian development along their longitudinal gradients, and 3) year-round seasonal differences in food sourcing along alpine stream gradients. The sampling was conducted seasonally from November 2013 to July 2014 within the glacial stream network at the base of Roseg and Tschierva glaciers (Bernina Massif, Switzerland), which have decreased in size rapidly with climate change (on average 40 m per year during the period 1997-2007 according to the Swiss Glacier Monitoring Network). The sampling sites were selected based on an earlier study of food webs in the same catchment in 1997. At each of the 4 sampling sites, we collected the most common macroinvertebrate taxa and their potential food sources, including primary producers (algae, biofilms, detritus) and riparian vegetation (grasses, shrubs, leaf material). The variability in isotopic signatures (i.e., carbon and nitrogen isotope ratios ; δ13C and δ15N) for macroinvertebrates and their potential food sources was then analyzed across seasons and sites. The spatial (between-site) and temporal (seasonal) differences in isotopic signatures provide information on year-round changes in macroinvertebrate feeding habits along the longitudinal alpine stream gradients, thus allowing a better understanding of functional shifts in these ecosystems. Furthermore, by showing potential shifts in macroinvertebrate food acquisition during the glacier recession, our results reveal how alpine stream macroinvertebrates could change their feeding habits in response to climate-induced environmental changes.

glacier streams; macroinvertebrates; stable isotopes; climate change; food sourcing

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