Ontogenetic shift in the trophic role of the invasive killer shrimp Dikerogammarus villosus: a stable isotope study

Abstract

The introduction of the amphipod Dikerogammarus villosus in European fresh waters is to date recognized as a threat to the integrity of invaded communities. Predation by D. villosus on native benthic invertebrates is assumed as the key determinant of its ecological impact, yet available information describe the species as a primary consumer as well as a carnivore depending on local conditions. Here, we assessed the trophic position (TP) of D. villosus in Lake Trasimeno, a recently invaded lentic system in central Italy, using the CN isotopic signatures of individuals captured in winter spanning two orders of magnitude in body size. TP estimations were compared with those characterizing the native amphipod Echinogammarus veneris and other representative invertebrate predators. On average, D. villosus showed a trophic position higher than E. veneris, and comparable with that of odonate nymphs. An in-depth analysis revealed that large-sized individuals had a trophic position of 3.07, higher than odonates and close to that of the hirudinean predator Erpobdella octoculata, while small-sized specimens had a trophic position of 2.57, similar to that of E. veneris (2.41). These findings indicate that size-related ontogenetic shifts in dietary habits may per se vary the nature of the interaction between Dikerogammarus villosus and native invertebrates from competition to predation. Information collated from published isotopic studies corroborated the generality of our results. We conclude that intra-specific trophic flexibility may potentially amplify and make more multifaceted the impact of the species on other invertebrate species in invaded food webs.

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.…”

“…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 .…”

Biological Invasions Affect Resource Processing in Aquatic Ecosystems: The Invasive Amphipod Dikerogammarus villosus Impacts Detritus Processing through High Abundance Rather than Differential Response to Temperature

“…However, the high density of invaders compared with natives may lead to the exhaustion of the resource in sites with relatively low leaf detritus levels. In addition, the flexible feeding habits of D. villosus could affect the community structure as competition for resources may lead to the increased predation of macroinvertebrates and fish eggs as the detrital resource reduces, the D. villosus population matures and its trophic level increases [ 104 , 105 ]. The high density of invasive shredders may also increase the nutrient load of affected water courses, with an increase in FPOM leading to possible eutrophication in freshwater systems with high seasonal allochthonous inputs [ 106 ].…”

The validation case on invasive crustaceans of the LifeWatch ERIC Internal Joint Initiative: State of the art and next steps forward

“…Stable isotopic data were collated from the literature to provide extensive, standardized, and spatially-explicit information on the trophic habits of the study species at different spatial scales. Stable isotopes analysis has gained huge popularity for the study of aquatic food webs in the last decades, allowing for robust comparisons of species dietary habits at a local as well as regional and global scale (e.g., Mancinelli, 2012;Annabi et al, 2018;Pethybridge et al, 2018;Mancini et al, 2021;Mancini et al, 2022). This methodology is currently recognized as a key tool to deepen the understanding of ecosystem processes and functioning and to evaluate the response of aquatic ecosystems to anthropogenic impacts, including global climate change (Mancinelli and Vizzini, 2015;Gautam and Lee, 2016).…”