Assessing the ecophysiology and ecological impacts of quagga mussels (Dreissena rostriformis bugensis) in Lake Geneva – QUALAG

The quagga mussel (Dreissena rostriformis bugensis) is an invasive species recognized as particularly threatening freshwater ecosystems in Europe and North America. Its invasion contributes to the standardization of natural habitats and causes a loss of biological diversity through the decline and disappearance of local species. The settlement of this filter-feeding mollusc is also likely to impact human health because it can bring, concentrate and propagate various pathogens. Hence, the quagga disrupts important economic activities and ecosystem services provided by a lake, such as fishing, water supply or navigation. QUALAG aims to evaluate the effects of the proliferation of the quagga mussel in the largest deep natural lake in Western Europe (Lake Geneva), with many ecological, sanitary and economic stakes. The first step is to participate to the effort to quantify the quagga densities and to map them at the ecosystem scale. We predict that biomasses will increase in deep water sections due to a densification of populations and especially their aging age structure. Then, we will proceed by investigating the growth rates of the quagga mussel, as functional impacts are biomass-dependent. Subsequently, we aim to estimate its current and future functional impact through the effects of filtration and retention of key elements like phosphorus by mussels. The main objective of QUALAG is therefore to assess, at the scale of an entire ecosystem, which can serve as a model for other peri-alpine deep lakes, the importance of the quagga mussel in the food web and some biogeochemical cycles. Our goal is to develop a simplified model capable of forecasting future changes, particularly in response to the growth and ageing of mussel populations. Note that QUALAG aligns well with the goal of the 2022-2030 national action plan outlined in the National Biodiversity Strategy 2030. This plan is geared toward preventing the introduction of new species and managing existing ones.