Same Habitat, Different Responses: Population Dynamics of Two Sympatric Invader Corbicula Species

Invasive species require long-term characterization of their shifting population dynamics to understand their environmental impacts and socio-economic effects. The dynamics of freshwater bivalves depend on their biology, which is influenced by the vulnerability of the ecosystems. This study evaluates the coexistence of Corbicula fluminea and C. largillierti in a stream in the Argentine Pampa, integrating density, size, and reproduction. In this stream, characterized by a temperate climate and hydrological fluctuations, live specimens of both species were sampled monthly using a 0.07 m2 cylinder. The anteroposterior length of each specimen was measured, and size distributions were analyzed by decomposing normal modes using the least-squares method. Gonadal cycles were compared with data from the previous literature. Since 2004, C. fluminea has dominated the system with significantly higher densities. Both species exhibited contrasting reproductive cycles. Hydrological instability in the stream limited both species. C. fluminea dominated due to its greater resilience and longevity under stress. In contrast, C. largillierti prioritized initial rapid growth, making it more sensitive to fluctuations. These results highlight that environmental instability conditions invasive success and interspecific competition in freshwater systems.