Biological control for NICS populations, it could be viable way to contrast biodiversity loss

The introduction and establishment of non-indigenous species (NICS) are widely recognized as one of the major drivers of biodiversity loss globally, especially within freshwater ecosystems, which are highly vulnerable due to their Connection, rather than confinement, facilitates the dispersal of introduced species and highlights the strong link with human activities. Among the most impactful NIS in Europe are nonindigenous crayfish species (NICS), such as Pacifastacus leniusculus (signal crayfish), which were initially introduced for aquaculture and fishery purposes. Over time, however, these species have demonstrated highly invasive potential, leading to the displacement of native species particularly the native white-clawed crayfish Austropotamobius pallipes and contributing to the spread of the crayfish plague (Aphanomyces astaci), a deadly disease for European native crayfish. This thesis investigates the feasibility and implications of applying biological control as a management strategy for invasive crayfish populations, with a specific focus on P. leniusculus. Biological control, defined as the deliberate use of natural enemies such as predators, parasites, or pathogens to suppress invasive species, has been widely employed in terrestrial environments but remains controversial and underdeveloped in aquatic systems. I conducted a study on the spread of microsporidian parasites in populations of A. pallipes. Molecular techniques were employed to identify Astathelohania contejeani and Nosema austropotamobii in macroscopically affected white-clawed crayfish. These two microsporidia produce similar macroscopic lesions and histological features, with few distinct diagnostic traits available to reliably differentiate between them. During this study, multiple populations infected by A. contejeani were detected, whereas N. austropotamobii was found less frequently. Astathelohania appeared to be more widespread in the wild and remains present and abundant in native crayfish populations, without causing high levels of infection or mortality. Based on these findings, A. contejeani could potentially be considered as a biological control agent against non-indigenous crayfish species (NICS), such as P. leniusculus, pending being virulent for this species, without causing substantial detrimental effects on native populations, which have not exhibited high mortality rates attributable to the pathogen. Moreover, A. contejeani exhibited a wider tissue tropism, affecting organs such as the cardiac muscle more frequently than Nosema austropotamobii. This characteristic suggests that A. contejeani may be a more promising candidate for our intended application. Despite the potential advantages of biological control, before this biological control strategy can be considered viable, it is essential to experimentally assess, under controlled conditions, the transmissibility of A. contejeani from the native to the non-native crayfish species, as well as to evaluate the efficiency of oral transmission and the virulence. To assess the feasibility of this tool for biological control, I performed infection experiments under specific controlled conditionsIn fact. Previous studies on this microsporidian was conducted before the two host species, A. contejeani and N. austropotamobii, had been identified. Therefore, it is necessary to re-evaluate its transmission.