Changes in the macrobenthic community structure following the introduction of the invasive algae Didymosphenia geminata in the Matapedia River (Qu,bec, Canada)

In July 2006, blooms of Didymosphenia geminata (didymo) were, for the first time, officially observed and identified in the Matapedia River, an Atlantic salmon river of the Gaspesie peninsula (Qu,bec, Canada). This invasive diatom can form thick and extensive benthic layers in stable flow and oligotrophic rivers. This study aimed to evaluate the potential effect of didymo on the macrobenthic community structure of the Matapedia River. Macrobenthic samples were obtained in 2006, upstream of the blooms and, at the same sampling sites a year later, when they were affected by didymo. The Causapscal River remained free of didymo blooms for both years; therefore, this tributary is considered as a control site. Results show a significant difference (P < 0.001) in the community distribution before and after didymo presence in two of the three sites. Significant data show an increase Chironomidae proportions in all the sites (P = 0.011). Significantly higher benthic macroinvertebrate (BMI) densities were also observed in 2007 (P < 0.001). Simpson's Evenness Index and total family richness was not significantly different when comparing pre- and post-incursion data (P = 0.90 and P = 0.83, respectively). Nevertheless, it is concluded that the presence of didymo has an effect on the base of the aquatic food web of the Matapedia River. This study is the first to assess the effect of this invasive alga on BMIs in Eastern Canada.