Effect of discharge and habitat type on the occurrence and severity of Didymosphenia geminata mats in the Restigouche River, eastern Canada

• Published in: Ecohydrology
• Main Authors: Gillis, Carole‐Anne, Dugdale, Stephen J., Bergeron, Normand E.
• Other Authors: Restigouche River Watershed Management Council, Conseil de l'eau Gaspésie-Sud, NSERC-FRQNT BMP-Innovation, New Brunswick Wildlife Trust Fund (NBWTF), Atlantic Salmon Conservation Foundation (ASCF), Fondation de l'Université du Québec (FUQ)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2018
• Subjects: Canada; Atlantic salmon
• Online Access: http://dx.doi.org/10.1002/eco.1959; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Feco.1959; https://onlinelibrary.wiley.com/doi/pdf/10.1002/eco.1959

Abstract Since 2006, the Restigouche River watershed, eastern Canada, has been affected by nuisance growths of the mat‐forming diatom, Didymosphenia geminata . In 2010, in view of the potential impacts of this alga on the local Atlantic salmon fishery, we created a volunteer monitoring network to assess D . geminata mat severity within the watershed. Over the course of 6 monitoring summers, more than 1,200 observations of D . geminata mat severity were reported in 20 subwatersheds of the Restigouche River basin. Observations were mapped to illustrate the yearly severity of D . geminata mats throughout the watershed. Metrics were then extracted from this dataset to assess the spatial and temporal variability of mat severity. At the reach scale, D . geminata occurrence was predominantly found in riffles compared to any other river habitat type. At the watershed scale, a two‐sample Kolmogorov–Smirnov test highlighted a significant effect of maximum spring discharge on mean annual D . geminata mat severity, indicating that when maximum spring discharge is high, severity of D . geminata mats in the following months is significantly lower. Additionally, maximum spring discharge explained 71% of the variability in annual mat severity. This study contributes to the understanding of mat severity dynamics and illustrates the value of volunteer monitoring networks for studying complex ecosystem dynamics.