Food web structure in a harsh glacier-fed river.

Leonie R Clitherow,Lee E Brown,Jonathan L Carrivick,Louis-Felix Bersier

doi:10.1371/journal.pone.0060899

Abstract

Glacier retreat is occurring across the world, and associated river ecosystems are expected to respond more rapidly than those in flowing waters in other regions. The river environment directly downstream of a glacier snout is characterised by extreme low water temperature and unstable channel sediments but these habitats may become rarer with widespread glacier retreat. In these extreme environments food web dynamics have been little studied, yet they could offer opportunities to test food web theories using highly resolved food webs owing to their low taxonomic richness. This study examined the interactions of macroinvertebrate and diatom taxa in the Ödenwinkelkees river, Austrian central Alps between 2006 and 2011. The webs were characterised by low taxon richness (13–22), highly connected individuals (directed connectance up to 0.19) and short mean food chain length (2.00–2.36). The dominant macroinvertebrates were members of the Chironomidae genus Diamesa and had an omnivorous diet rich in detritus and diatoms as well as other Chironomidae. Simuliidae (typically detritivorous filterers) had a diet rich in diatoms but also showed evidence of predation on Chironomidae larvae. Food webs showed strong species-averaged and individual size structuring but mass-abundance scaling coefficients were larger than those predicted by metabolic theory, perhaps due to a combination of spatial averaging effects of patchily distributed consumers and resources, and/or consumers deriving unquantified resources from microorganisms attached to the large amounts of ingested rock fragments. Comparison of food web structural metrics with those from 62 published river webs suggest these glacier-fed river food web properties were extreme but in line with general food web scaling predictions, a finding which could prove useful to forecast the effects of anticipated future glacier retreat on the structure of aquatic food webs.

Highlights

One of the main organisational components in an ecosystem is the food web, a description of ‘who-eats-whom’ [1,2]
The macroinvertebrate assemblage in the Odenwinkelkees river was dominated by the chironomid genus Diamesa, which is typical of cold streams in Europe [16,19,21,22,23]
Warmer water temperature is linked strongly to the turnover of glacial stream community composition, with the introduction of previously unresolved species that compete with existing species for food sources

Summary

Introduction

One of the main organisational components in an ecosystem is the food web, a description of ‘who-eats-whom’ [1,2]. Knowledge of the many feeding linkages within an ecosystem is vital to comprehend how a community of individuals can persist over time, as well as describing its stability with respect to environmental or biological perturbations [2,3] This is of particular importance in terms of climatic change which is likely to alter hydrological and thermal regimes markedly, leading to major changes in aquatic food webs [5,6,7]. Increased attention is being paid to alpine rivers as their fragility and vulnerability to climate change becomes more apparent [10,11,12,13] Glaciers in these environments are retreating and downwasting rapidly, changing river flow and thermal regimes, fluvial geomorphology and water chemistry [14]

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Conclusion