Factors influencing the presence and relative abundance of Didymosphenia geminata: impact on the composition of diatom assemblages over a broad latitudinal gradient in Chilean rivers

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This study explored the abiotic factors influencing Didymosphenia geminata blooms and the combined effect of D. geminata and abiotic factors on local diatom assemblages in 13 Chilean watersheds across a broad latitudinal range (37°–47° S). To understand the multi-scale drivers, we used generalized linear mixed-effects models to assess the abiotic factors most influential on D. geminata presence and relative abundance. We then explored the effects of D. geminata and abiotic factors on the α- and β-diversity of diatom assemblages using generalized linear models and permutational analyses of variance, respectively. Three watersheds lacked D. geminata and another three had low relative abundance. Seasonally, the relative abundance of D. geminata was significantly higher in spring than in autumn. We found positive correlations between elevation, river order, pH and D. geminata presence and relative abundance, while water temperature was negatively correlated with D. geminata relative abundance. Diversity indices were significantly influenced by watershed and to a lower extent by the presence of D. geminata. We found significant spatial (i.e. between watersheds along a south–north latitudinal gradient) and temporal (i.e. between seasons) variations in β-diversity of diatom assemblages. Moreover, increasing relative abundance of D. geminata in the assemblage was correlated with lower diatom diversity. In addition, the compositions of diatom assemblages with D. geminata were more alike and less variable than those in non-invaded sites. This study is a first attempt to understand the multi-scale drivers of diatom assemblages in Chilean lotic ecosystems.