Abstract
Climate change is driving the thinning and retreat of many glaciers globally. Reductions of ice-melt inputs to mountain rivers are changing their physicochemical characteristics and, in turn, aquatic communities. Glacier-fed rivers can serve as model systems for investigations of climate-change effects on ecosystems because of their strong atmospheric–cryospheric links, high biodiversity of multiple taxonomic groups, and significant conservation interest concerning endemic species. From a synthesis of existing knowledge, we develop a new conceptual understanding of how reducing glacier cover affects organisms spanning multiple trophic groups. Although the response of macroinvertebrates to glacier retreat has been well described, we show that there remains a relative paucity of information for biofilm, microinvertebrate, and vertebrate taxa. Enhanced understanding of whole river food webs will improve the prediction of river-ecosystem responses to deglaciation while offering the potential to identify and protect a wider range of sensitive and threatened species.
Highlights
Climate change is driving the thinning and retreat of many glaciers globally
Number of papers responses of biota to shrinking glaciers as part of multitrophic river ecosystems. This new multitaxonomic response framework is used subsequently to explore the consequences for how whole-river food webs can be expected to respond to ongoing glacier retreat. Such an approach is required to inform alpine conservation strategies by providing a holistic food-web context for the multiple cold-environment endemic species that are found in glacier-fed rivers around the world (e.g., Brown et al 2009, Giersch et al 2016)
Because glacier-fed river systems will respond rapidly to climate change, any reassembly of food webs could help to identify structural and functional changes that could be monitored in running waters across other biogeographical regions (Woodward et al 2010)
Summary
Downloaded fr9o0m0htBtpiso:S/c/iaecnacdeemicO.ocutop.bceorm2/0bi1o7sc/iVeoncl.e6/a7rNtioc.l1e0-abstract/67/10/897/4201673 by University of Leeds user on 17 November 2017 https://academic.oup.com/bioscience. Despite increases in macroinvertebrate richness and biomass, glacier retreat is reducing the beta and gamma diversity of alpine rivers globally (Brown et al 2007, Jacobsen et al 2012, Finn et al 2013) This is driven by the extirpation of cold stenothermic species dependent on the physicochemical environment provided by ice-melt inputs (Giersch et al 2016). Vertebrates, for example, provide an exception to these trends, because desman species (G. pyrenaicus) and the Pyrenean brook newt (C. asper) preferentially occupy highvelocity mountain rivers in the Pyrénées, increasing their density and in turn biomass with reducing glacier influence (Comas and Ribas 2015, Biffi et al 2016) They appear first at intermediate levels of glacier catchment cover (figure 4), in contrast to ubiquitous macroinvertebrates. Periods of low or no flow could introduce trophic cascades of variable magnitude and may induce the compensatory reorganization of whole foodweb cores, influencing all species within a community both directly and indirectly (Ledger et al 2013, Lu et al 2016)
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