Pressure-Induced Shifts in Trophic Linkages in a Simplified Aquatic Food Web

Maarten Schrama,S Henrik Barmentlo,Richard S P Van Logtestijn,Martina G Vijver,Ellard R Hunting,Peter M Van Bodegom

doi:10.3389/fenvs.2017.00075

Abstract

It is essential to understand effects of existing and emerging anthropogenic stressors on the structure of aquatic food webs in more natural settings, to obtain realistic predictions on how they can affect major ecosystem properties and functioning. We therefore examined whether 1) realistic concentrations of key agricultural pesticides and nutrients induce shifts in trophic linkages 2) observed changes in trophic linkages are qualitatively different between the green (algal-based) and brown (detritus-based) part of the food web. To this end, we exposed a simplified, yet realistic freshwater invertebrate community to environmentally relevant concentrations of three anthropogenic pressures (eutrophication; the herbicide terbuthylazine; and the insecticide imidacloprid) in a full factorial mesocosm design. Trophic linkages and the changes therein were assessed measuring stable isotopes of natural carbon and nitrogen. Results show that the green and brown part of the food web react qualitatively different to interacting pressures. Whereas herbivorous species react mainly to the nutrients and herbicides and the synergistic interaction between these, species in the detritivore part of the food web were affected by insecticide applications and interactions with nutrients. These results suggest that agricultural pressures can induce shifts in trophic linkages, but that they can have contrasting effects on the different parts of the food web. Such antagonistic and synergistic interactions can provide powerful explanations for observed responses of ecosystems to interacting stressors. These findings may have important implications for our understanding on interactions of agricultural stressors and their propagation in aquatic food webs.

Highlights

Aquatic ecosystems harbor a diverse array of organisms that interact across trophic levels (Wallace et al, 1997)
We find different δ15N/ δ14N ratios between species, indicating different trophic levels (Figure 1). For both N and C stable isotopes, positive correlations were observed between a number of species (C. dipterum, D. magna, Cyclops sp., L. stagnalis, and periphyton) (Tables 2, 3), suggesting a similar reaction to changing environmental conditions or trophic interactions
By studying the single and joint effects of stressors at environmentally realistic concentrations to an aquatic food web, we show that a number of key species in the community can alter their trophic position and food source as a result of the different stressors

Summary

Introduction

Aquatic ecosystems harbor a diverse array of organisms that interact across trophic levels (Wallace et al, 1997). Aquatic animals can react to such pollutants by altering their food source, leading to changes in predation efficiency (Smith and Weis, 1997; Schulz and Dabrowski, 2001), bioturbation (Hinkle-Conn et al, 1998; Hunting et al, 2013) and nutrient cycling (Fleeger et al, 2003) Such alterations in trophic linkages can be regarded as rippling effects in food webs which may result in ecosystemwide effects and subsequently affect ecosystem functioning and the services it provides (Fleeger et al, 2003; Corvalan et al, 2005). How anthropogenic pressures propagate through trophic linkages in aquatic food webs and inherent effects on ecosystem processes remains poorly understood

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