Stoichiometric constraints modulate impacts of silver contamination on stream detritivores: an experimental test with Gammarus fossarum

Abstract

SUMMARY1. Organisms commonly face multiple stresses in ecosystems, among which are toxic substances that add to natural ecological constraints such as insufficient resource quality. The combined effects of these stressors on species and ecosystems remain poorly investigated. 2. We hypothesised that feeding on high-quality resources in terms of phosphorus (P) content will improve the physiological state of consumers and thus increase tolerance to episodic metal stress by silver (Ag). We used a detritivorous crustacean from streams, Gammarus fossarum, to test this hypothesis. 3. The experimental design involved two phases. In the first phase, gammarids were fed ad libitum for 15 days to evaluate the effect of food quality on their energetic status. Gammarids were placed in laboratory microcosms and allowed to feed on two leaf species, alder and sycamore, that were colonised by aquatic fungi and experimentally enriched with P. At the end of this feeding period, we determined (i) food consumption, (ii) energetic reserves and (iii) physiological and behavioural states. In the second phase, gammarids previously consuming food of different quality were exposed to dissolved Ag (0, 0.5 and 1 lg L À1) for 4 days to investigate the physiological and behavioural responses of the consumers. 4. Elevated P concentrations in leaf litter increased the energetic reserves and locomotor activity of G. fossarum. Gammarids exposed to Ag had a low glycogen content, regardless of the Ag concentration and leaf P concentration, suggesting significant energy allocation to several aspects of organism maintenance (e.g. detoxification or compensatory mechanisms). In most cases, this investment appeared to prevent gammarids from carrying out lipid peroxidation (indicating cell membrane damage), except for those gammarids feeding on leaves with the highest P concentration. 5. Higher energetic storage (measured as glycogen content), related to higher elemental food quality, did not lead to a systematic increase in consumer tolerance to Ag, gammarids being unable to compensate for negative effects of Ag at the concentrations tested.

Nutrient–insecticide interactions decouple density‐dependent predation pressure in aquatic insects

“…Increased feeding is generally thought to offset the energetic burden associated with the physiological elimination of toxic substances (e.g. Biggs, 1996;De Haas et al, 2002;Goedkoop, Spann & Akerblom, 2010;Arce-Funck et al, 2016). However, the likely surplus productivity was channelled to the top predator in the community, A. capitata, which responded by increased body size.…”

Fostering integration of freshwater ecology with ecotoxicology

“…This led Arce‐Funck et al . () to hypothesise that the consumption of leaf litter enriched with phosphorus (P) can mitigate metal stress on litter‐consuming detritivores. Consumption of leaves rich in P did indeed increase the energy reserves and activity of the tested detritivore, the amphipod Gammarus fossarum .…”

“…Nutrient content of organic matter is assumed to be an important factor determining food quality for detritivorous consumers (Danger, Gessner & B€ arlocher, 2016). This led Arce-Funck et al (2016) to hypothesise that the consumption of leaf litter enriched with phosphorus (P) can mitigate metal stress on litter-consuming detritivores. Consumption of leaves rich in P did indeed increase the energy reserves and activity of the tested detritivore, the amphipod Gammarus fossarum.…”

“…Rather, both studies (i.e. Alexander et al ., ; Arce‐Funck et al ., ) indicate that in addition to indirect nutrient effects, characteristics of populations and communities can cause unexpected responses to contaminant exposure (see Fig. ), and thus require consideration in ecotoxicological assessments and environmental risk management of chemicals.…”

Interactive Impacts of Silver and Phosphorus on Autotrophic Biofilm Elemental and Biochemical Quality for a Macroinvertebrate Consumer

“…However, the interactive effects of these stressors on ecosystem functioning remain poorly understood. By alleviating organisms’ nutrient limitation, increases in nutrient concentrations might potentially increase organisms’ tolerance to contaminants (Arce-Funck et al, 2016). In contrast, by altering water quality parameters, such as dissolved oxygen concentrations, one could expect changes in contaminant bioavailability (Skei et al, 2000) and/or intensification of the damages caused by the contaminants on already stressed organisms (Rattner and Heath, 2003).…”