An invasive mussel is in trouble: How do glyphosate, 2,4-D and its mixture affect Limnoperna fortuneiʹs survival?

•Mussel metabolism and herbicides induce fluctuations in dissolved oxygen in water.•L fortunei mortality increases when glyphosate is present alone or mixed with 2,4-D.•The mixture of glyphosate and 2,4-D acts additively on L. fortunei survival. Contamination and biological invasions are important factors that alter the functioning of freshwater systems. We carried out two experiments involving daily measurements of dissolved oxygen (DO) and Limnoperna fortunei mortality: 1) the impact of DO on mussel survival mediated by glyphosate, 2,4-D and their mixture was analysed in a 22-day indoor experiment (IE) under controlled conditions using microcosms with L. fortunei, with and without air supply; and 2) the effect of each herbicide and their mixture on mussel accumulated mortality was compared in a 18-day outdoor experiment (OE) using mesocosms without air supply, with and without L. fortunei. Results showed that glyphosate, alone or mixed affected L. fortunei survival both directly and indirectly. In IE we observed direct toxicity of glyphosate in treatments with air supply, with accumulated mortality of 20.0% for glyphosate and 10.0% for the mixture. In OE, L. fortunei deepened the changes in the patterns of DO fluctuations driven by the herbicides, which led to hypoxia in the system. The accumulated mortality was 46.7, 8.6 and 48.2% for glyphosate, 2,4-D and the mixture, respectively. This study contributes to the understanding of the mechanisms that control the invasion of L. fortunei in freshwater systems influenced by agrochemicals. [Display omitted]