A microbial perspective on biological invasions in aquatic ecosystems

Microorganisms are essential components of all aquatic ecosystems and are primarily responsible for biogeochemical cycles and key environmental processes. Despite their potential to influence the ecological functioning of biological communities and ecosystems at a global scale, the mechanisms of microbial invasions still lack specific and generalizable theories. Here, we review some of the ecological mechanisms, among those relevant under the global change scenario, which may facilitate the spread of microbial invaders, with a specific focus on aquatic prokaryotes (i.e. Bacteria). We summarize a selection of ecological features of vulnerable microbial communities (functional and structural stability, diversity, invasibility, and invasiveness) and environmental stressors for invasions (temperature increase, pollution, nutrients and resources fluctuations, and food web alterations). Owing to the rapid microbial adaptation to laboratory conditions, straightforward experimental approaches appear as suitable and informative tools to explore the invasion mechanisms in artificially assembled communities. We conclude by delineating future research steps required for a better understanding of the potential consequences of microbial invasions in the aquatic environment.