Impact of food type on respiration, fractionation and turnover of carbon and nitrogen stable isotopes in the marine amphipod Gammarus aequicauda (Martynov, 1931)

Abstract

This study experimentally determined the impact of food source type on turnover rate and trophic enrichment factors (TEFs or Δ) of δ 13 C and δ 15 N, as well as on respiration rate, in captive populations of the marine amphipod Gammarus aequicauda. Gammarus aequicauda (318 individuals) were fed ad libitum with three food sources animal, algae, and dead Posidonia oceanica leaves (also called "litter"), varying in palatability, digestibility, nutritional qualities and isotopic compositions, for between four and six weeks in a controlled feeding experiment. The resulting death rate was lower for the amphipods fed with animal treatment (30.9%) than for individuals fed with algal (65.9%) or litter treatment (64.4%), indicating a better fitness of the individuals fed with the animal food source. Respiration rates also differed highly among the treatments. Animal treatment showed higher respiration rates than algal and litter treatments, potentially due to the toxicity of the algae and the very low nutritional quality of the litter. Amphipods fed with these treatments might have entered in a "low activity state" to cope with these unsuitable food sources, inducing low respiration rates. Due to the very low assimilation and toxicity of the algae source, turnover rate for δ 13 C was impossible to determine. Turnover rate for δ 13 C was much faster (half-life = 12.55 days) for amphipods fed with the animal food source than for amphipods fed with litter (half-life = 51.62 days), showing the faster assimilation of the most nutritionally optimal food sources by G. aequicauda. Turnover for δ 15 N was impossible to determine because the amphipods were already at isotopic equilibrium at the beginning of the experiment. Despite the detritus feeder status of Gammarus aequicauda, TEFs for the animal treatments were in accordance with values generally found for carnivorous organisms (Δ 13 C = 0.9 ± 0.7‰; Δ 15 N = 2.9 ± 0.6‰). TEFs for the litter treatment were in accordance with values generally corresponding to detritivorous organisms (Δ 13 C = 1.2‰; Δ 15 N = 1.0 ± 0.4‰). SIAR mixing model outputs obtained with these new TEF values were more constrained and coherent than outputs obtained with general literature TEFs. This study thus demonstrated the non-negligible impact of the food source on Gammarus aequicauda physiological status, fitness and turnover rates, but also on TEFs-highlighting the importance of TEF experimental calculations for every potential food source of a given organism to ensure more robust isotopic data interpretation.

Behavior of Gammarus aequicauda (Crustacea, Amphipoda) during predation on Artemia (Crustacea, Anostraca): New experimental results

“…New and previously published data showed that G. aequicauda, which is often described as a herbivore and detritivore (Cummins & Klug, 1979;Graca et al, 2001), intensively consumes different animals, which are an essential part of its diet (Remy, Darchambeau, Melchior, & Lepoint, 2017;Shadrin et al, 2019). Vladimir Yakovenko http://orcid.org/0000-0001-8926-0180 Elena Anufriieva http://orcid.org/0000-0002-6237-7941…”

Components of standard metabolic rate variability in three species of gammarids

“…The key results presented in the present paper do not seem to depend on methodological bias. The individual metabolic rates of aquatic organisms are assessed in the literature by various methods including flow through (Vignes et al, 2012), closed system (Toman and Dall, 1998;Remy et al, 2017) and intermittent flow (Svendsen et al, 2016). The latter two methods have been shown to be more sensitive than the former to oxygen stress and accumulation of individual excretion products (Franke, 1977;Gnaiger, 1983;Lampert, 1984).…”

“…Lekanesphaera monodi (Vignes et al, 2012); and (v) resource quality, with a direct response of standard metabolic rates to increasing resource quality, e.g. Gammarus aequicauda fed on live prey or Flabellia petiolata or P. oceanica leaves (Remy et al, 2017).…”

Importance of suspended particulate organic matter in the diet of Nephrops norvegicus (Linnaeus, 1758)

“…These values contrast with widely-used values from previous meta-analysis 56 that present averages from 61 different species of aquatic and terrestrial vertebrates and invertebrates in a variety of taxa: arthropods, molluscs, nematodes, birds, fish and mammals (for information, values in 56 were 0.5 ± 0.13‰ for δ 13 C and 2.3 ± 0.18‰ for δ 15 N). Nevertheless, we chose the mantis shrimp values 54 , firstly, on the basis that these fractionation values were calculated from a decapod crustacean: taxonomic relatedness is important due to evidence that TEFs are taxon-specific due to shared physiological processes at taxon level [57][58][59][60][61] . Secondly, the values in 54 represented lipid-corrected stable isotope ratios for consumers and prey, as also used in our study, and were from a diet shift controlled laboratory experiment.…”