Population dynamics and expansion of Crangonyx pseudogracilis, a potentially invasive amphipod

One of the main drivers of biodiversity loss is the introduction of exotic invasive species. In 2011, an abundant population of Crangonyx pseudogracilis, a freshwater amphipod native to North America, was detected in Portugal. This study allowed us to better understand its biology, analysing the population dynamics in a temporary river and a small lake for one year, and to follow its expansion. Our results showed that this species reproduces in the temporary river during most of the year, but in the lake only from March to July. Amphipod density decreases from May to October and increases from November to April. As usual, females were larger than males, but the proportion of females was higher than males at both sampling locations. Finally, we noticed a great increase in C. pseudogracilis distribution area in relation to what was observed in 2014, with a diffusion coefficient of 2495.27 km2/year and a spread rate of 26 km/year. However, no overlap was yet detected between native and exotic amphipod species.