First Insights into Nematode Parasites in Non-native Freshwater Chelonians in Portugal

Abstract

Parasites are increasingly recognized as essential components of ecological balance, influencing host populations, trophic interactions, and ecosystem dynamics. In freshwater turtles, the diversity and distribution of parasite fauna are strongly associated with geographic distribution, invasive status, population density, and ecological traits of different species. This study aimed to identify the nematodes present in freshwater turtles captured in Portugal, in three distinct locations, Ria Formosa, Sintra-Cascais Natural Park, and the Lisbon Metropolitan Area, where native species ( Mauremys leprosa and Emys orbicularis ) coexist with several invasive species. Turtles were captured using fyke nets, hoop traps, and basking traps, with monitoring conducted for a minimum of five days per site. Captured individuals were euthanized under veterinary supervision and subjected to necropsy. A total of 88 turtles were necropsied, including 56 from Ria Formosa, 15 from the Lisbon Metropolitan Area, and 17 from the Sintra-Cascais Natural Park. Parasites were collected from the gastrointestinal tract and internal organ washings and subsequently examined under a binocular microscope. The genus Serpinema was widely identified in several non-native freshwater turtle species in Portugal. In Ria Formosa, 6 specimens of Serpinema were recorded in Trachemys scripta , 9 in Mauremys sinensis , and 1 in Graptemys pseudogeographica , all occurring in sympatry with the native species M. leprosa . In the Lisbon Metropolitan Area, Serpinema was also detected in non-native species, with 2 specimens recorded in Pseudemys concinna , 1 in T. scripta , and 15 in G. pseudogeographica . A similar pattern was observed in the Sintra-Cascais Natural Park, where Serpinema was identified in several invasive species, namely 6 specimens in Pseudemys peninsularis , 6 in M. sinensis, 12 in T. scripta , 4 in P. concinna , and 1 in Mauremys reevesii . Additionally, other parasite genera were exclusively associated with non-native hosts. In Ria Formosa, 2 specimens of the genus Telorchis were recorded in T. scripta , while 4 specimens of Spiroxys were identified in M. sinensis . In contrast, the genus Falcaustra was found exclusively in native hosts, with 19 specimens identified in M. leprosa , and was not detected in non-native turtles.To the best of our knowledge, this study represents the first record of Serpinema and Falcaustra in freshwater turtles in Portugal. These findings highlight the role of invasive turtles as potential hosts and vectors of parasites, with possible implications for native biodiversity and ecosystem functioning. This work contributes to filling the existing knowledge gap regarding the parasite fauna of freshwater turtles in Portugal and provides a basis for future studies on parasite transmission and associated ecological risks.