Introducing the Meal Unit for Gammarid (MUG®) as a standardized food substrate for in situ bioassays with the amphipod Gammarus fossarum
摘要
In situ feeding bioassays are recognized as relevant tools for assessing freshwater quality in biomonitoring programs. However, commonly used food substrates are sometimes more difficult to procure than substrates based on reference products. Using Gammarus fossarum as a model European freshwater amphipod species, the present study introduces MUG® (Meal Unit for Gammarid) as a standardized food substrate produced with reference ingredients for in situ feeding bioassays. Here, we investigated the suitability of MUG® for evaluating the impact of water chemical contamination on the feeding response of amphipods. To improve the interpretability of the field feeding assays for G. fossarum, we first modelled the influence of temperature on MUG® consumption rates via a laboratory-controlled conditions experiment. We then assessed the reliability and sensitivity of feeding assays using MUG® by performing in situ deployments at 20 stations monitored by French water agencies. We found in the field that MUG® in the absence of gammarids lost 17% (median; min. = 1%; max. = 23%) of their initial dry mass and that the total MUG® mass loss in the presence of gammarids was always significantly greater (median = + 48%; min. = + 10%; max. = + 82%) than that in the controls. Moreover, we highlighted the variation in observed feeding rate values (adjusted for water temperature) between sites, that is, significant induction (n = 7 sites) or inhibition (n = 4 sites) of MUG® consumption by gammarids compared with the median adjusted feeding rate observed at all sites. Our study revealed that the use of MUG® as a standardized food substrate during in situ feeding bioassays is a promising tool for the diagnostic assessment of water quality.