Resource requirements of four freshwater diatom taxa determined by in situ growth bioassays using natural populations from alpine lakes

We performed a series of in situ batch culture experiments to assess the resource requirements of common diatom taxa in alpine lakes of the central Rocky Mountains of North America. While physiological data are available on the resource requirements of some of these taxa, it is unclear whether intraspecific generalizations can be made across aquatic systems due to the potential development of ecotypes. In these experiments, we used amended lake water for a culture medium and natural diatom populations. Growth kinetics were determined for Asterionella formosa Hassall, Fragilaria crotonensis Kitton, Staurosirella pinnata (Ehr.) Williams and Round and Tetracyclus glans (Ehr.) Mills. Staurosirella pinnata, a historically abundant alpine diatom, had very low N and P requirements. Asterionella formosa and F. crotonensis, generally considered meso- or eutrophic species, exhibited low P requirements if N and Si were in moderate supply. Tetracyclus glans had the highest Si requirement. These experiments reveal that the recent changes in diatom community structure in these alpine lakes may be driven by changes in nutrient supply. We suggest that local diatom taxa and a natural culturing medium should be used to obtain more representative algal physiological data from a particular area.