Stable isotope analysis reveals trophic segregation between the invasive zebra mussel Dreissena polymorpha and the native duck mussel Anodonta anatina in Lake Trasimeno (Italy)

Abstract

Non-indigenous freshwater bivalves negatively affect invaded ecosystems through different mechanisms, including inter-specific competition for trophic resources. Here, we investigated in Lake Trasimeno (Central Italy) the diet of the invasive Dreissena polymorpha and the native Anodonta anatina. δ15N and δ13C stable isotopes were measured in winter and summer in bivalves, phytoplankton, and sedimentary organic matter (SOM); the relative dietary contributions of the two resources were determined using Bayesian mixing models. To elucidate the different carbon and nitrogen pools characterizing the study site, isotopic analyses were extended to zooplankton and to representatives of the benthic flora and macroinvertebrate fauna. Independently from the season, the two bivalves showed a limited trophic overlap, as mixing models indicated for D. polymorpha a diet based primarily on phytoplankton, while A. anatina relied mainly on SOM. Dietary differences were less marked in summer, when comparable isotopic values characterized phytoplankton and SOM. In winter, conversely, the trophic differentiation between the two species was more evident, and corresponded with a significant enrichment in SOM δ13C values, likely due to a substantial contribution of carbon deriving from decaying macrophytes. Whether differences in ecological and behavioral traits alone can explain the observed trophic segregation between the two species, or if they have actively shifted their diet to reduce competition for food is discussed. We conclude emphasizing the need of an advanced resolution of the influence of non-indigenous species on the flux of energy and matter in invaded lentic systems, including Lake Trasimeno.

Isotopic Overlap of Invasive and Native Consumers in the Food Web of Lake Trasimeno (Central Italy)

“…They were performed at the same location as this study and include δ 13 C and δ 15 N values of benthic invertebrates and zooplankton. The study by Ludovisi et al [ 59 ] was carried out in 2018 and coincided with the present investigation, while that of Mancini et al [ 58 ] was performed in February 2016. The isotopic characteristics of the components of the food web at the study site were assumed to have remained unchanged between the sampling years.…”

“…The isotopic data obtained in the present investigation were complemented with those published in Mancini et al [58] and Ludovisi et al [59]. They were performed at the same location as this study and include δ 13 C and δ 15 N values of benthic invertebrates and zooplankton.…”

“…Invertebrates were collected in a shallow embayment (approximate depth = 1 m) situated in front of the area where fish and crayfish were sampled. Details of the location are provided in Mancinelli et al [ 57 ], while information on the sampling procedures are included in Mancini et al [ 58 ] and Ludovisi et al [ 59 ]. In brief, the embayment has muddy bottoms and artificial rocky shores, characterized in winter by accumulations of decaying plant material, including P. australis leaf litter and mixed detritus of macrophytes belonging to the genera Myriophyllum , Potamogeton , and Vallisneria .…”

Does invasion by armored catfish shift trophic ecology of native fishes? Evidence from stable isotope analysis

“…However, trophic overlap does not necessarily indicate competition, which depends on the ratio of resource demand/supply, ecosystem productivity, and population densities (García et al, 2020). Low niche overlap is generally interpreted as evidence of resource partitioning between invasive and native species (e.g., Ludovisi et al, 2022).…”