Water Wars: competition between native and exotic isoetid species

International audience

إنجليزي. Among several global changes, invasion by exotic species is often pointed out as responsible for the decline of native species. Indeed, in the competition for space and resources, fast-growing species are generally more efficient than native ones. The natural lakes along the Aquitaine coast are home to unique and protected populations of isoetid macrophytes, which are declining in the last decades. The present study aims at testing the potential competition between the native isoetid Lobelia dortmanna and the exotic isoetid Sagittaria graminea, both coexisting in Lake Cazaux-Sanguinet, France. To achieve this, we set up a multi-year monitoring program across 1x1m quadrats, with three conditions: native species only, exotic species only, and mixed condition when both species occurred. Each individual in the quadrat was spatially mapped and its photosynthetic activity was measured, as well as its leaf length and width. Sediment samples were also collected to analyze differences in organic matter content and granulometry between the quadrats. Preliminary results show that, while substrate analysis indicates similar biotopes for both species, their co-occurrence triggered significant physiological and morphological responses. Additionally, the native and exotic species appeared to follow different patterns of spatial distribution. However, these first results did not necessarily indicate a negative effect of the exotic species on the native one. Further field sampling in the coming years will help clarify the temporal spatial dynamics of the two species.