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

Autotrophic biofilms are complex and fundamental biological compartments of many aquatic ecosystems. In particular, these biofilms represent a major resource for many invertebrate consumers and the first ecological barrier against toxic metals. To date, very few studies have investigated the indirect effects of stressors on upper trophic levels through alterations of the quality of biofilms for their consumers. In a laboratory study, we investigated the single and combined effects of phosphorus (P) availability and silver, a re-emerging contaminant, on the elemental [carbon (C):nitrogen (N):P ratios] and biochemical (fatty acid profiles) compositions of a diatom-dominated biofilm initially collected in a shallow lake. We hypothesized that (1) P and silver, through the replacement of diatoms by more tolerant primary producer species, reduce the biochemical quality of biofilms for their consumers while (2) P enhances biofilm elemental quality and (3) silver contamination of biofilm has negative effects on consumers life history traits. The quality of biofilms for consumers was assessed for a common crustacean species, Gammarus fossarum, by measuring organisms’ survival and growth rates during a 42-days feeding experiment. Results mainly showed that species replacement induced by both stressors affected biofilm fatty acid compositions, and that P immobilization permitted to achieve low C:P biofilms, whatever the level of silver contamination. Gammarids growth and survival rates were not significantly impacted by the ingestion of silver-contaminated resource. On the contrary, we found a significant positive relationship between the biofilm P-content and gammarids growth. This study underlines the large indirect consequences stressors could play on the quality of microbial biomass for consumers, and, in turn, on the whole food web

High stoichiometric food quality increases moulting organism vulnerability to pollutant impacts: An experimental test with Gammarus fossarum (Crustacea: Amphipoda)

International audienc

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

International audienceOrganisms 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. 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. 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 μg L−1) for 4 days to investigate the physiological and behavioural responses of the consumers. 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. 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

Stoichiometry of Plant Litter Decomposition in Stream Ecosystems

International audienceEcological stoichiometry is an approach of ecology aimed at understanding the causes and consequences of elemental imbalances in nature (mainly focusing carbon, nitrogen, and phosphorus), from molecular to ecosystem levels. Like most detritus in nature, plant litters are nutrient depleted, and both microbial decomposers and detritivores are exposed to large stoichiometric constraints. These nutritional constraints will ultimately control litter decomposition rates, nutrient mineralization, and affect, in turn, decomposers’ community structures. To consider such stoichiometric constraints could greatly help understanding the functioning of detritus-based ecosystems. In this chapter, focused on leaf litter, diverse examples of stoichiometric constraints at play at the detritus-decomposer interface in aquatic ecosystems are presented. The different steps involving stoichiometric processes and ultimately conducting to litter decomposition, from the production of leaf litter in the riparian zones of freshwater ecosystems to its incorporation in aquatic food webs and its potential recycling in freshwater ecosystems are discussed. Stoichiometric constraints arising between detritus and decomposers in freshwater ecosystems are then placed into the context of current global change. Finally, we highlight the limits of the stoichiometric approach as well as some complementary approaches and perspectives of work are proposed

Minor food sources can play a major role in secondary production in detritus-based ecosystems

International audienc

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

International audienc