Ecology of the stalked diatom, Didymosphenia geminata, in Sierra Nevada streams

Demographic patterns of the freshwater stalked diatom, Didymosphenia geminata, have changed in the past twenty five years resulting in an increase in its spatial and temporal coverage in new and native streams. This proliferation has raised concerns because the causes and ecological consequences of extensive growth remain largely unknown. Three research projects were conducted in Sierra Nevada streams to gain insight into its ecophysiology and to determine if D. geminata forms ecologically disruptive blooms.;The first study establishes D. geminata distribution patterns in Sierra Nevada streams as it relates to ion chemistry and bedrock geology. In this study, it was shown that distribution patterns were positively correlated with a high percentage of Ca2+ and SO4 2-, and meta-sedimentary bedrock and negatively correlated with Mg 2+ concentrations and volcanic bedrock.;The second study presents results from nutrient limitation experiments using nutrient diffusing substrate and the following set of nutrient amendments including NO3- and PO4-, as well as Ca2+, SiO3-, HCO 3-, SO42-. Results show that N most often limits benthic algae growth in study streams (3/7) while SiO 3-, HCO3-, and SO4 2- limited growth in one study stream each. Results provide some insight into possible unique nutrient requirements for bloom development.;The third study addresses the extent to which nuisance growth is ecologically disruptive. Results show that nuisance growth can create ecologically disruptive blooms by reducing benthic macroinvertebrate grazer populations, reduce relative contributions of autochthonous carbon to higher trophic levels, and possibly reduce food quality at the trophic base of impacted stream. Additionally, this study also shows that ecologically disruptive conditions quickly diminish with the influence of an unaffected tributary stream.;These studies add to the growing body of knowledge pertaining to D. geminata ecophysiology and provide important insights into the magnitude and possible mechanisms of ecological disruptions.