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

This study explored the abiotic factors influencing <i>Didymosphenia geminata</i> blooms and the combined effect of <i>D. geminata</i> 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 <i>D. geminata</i> presence and relative abundance. We then explored the effects of <i>D. geminata</i> 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 <i>D. geminata</i> and another three had low relative abundance. Seasonally, the relative abundance of <i>D. geminata</i> was significantly higher in spring than in autumn. We found positive correlations between elevation, river order, pH and <i>D. geminata</i> presence and relative abundance, while water temperature was negatively correlated with <i>D. geminata</i> relative abundance. Diversity indices were significantly influenced by watershed and to a lower extent by the presence of <i>D. geminata</i>. 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 <i>D. geminata</i> in the assemblage was correlated with lower diatom diversity. In addition, the compositions of diatom assemblages with <i>D. geminata</i> 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.