Ecology of the diatom Aulacoseira pusilla in oligotrophic mountain lakes, with implications for paleoclimate reconstructions

Abstract

Diatoms in lake sediments are used in paleoclimate reconstructions, particularly in treeless areas such as arctic and alpine regions. Some diatom species in the Aulacoseira group are often thought to bloom as lakes turnover (i.e., mix), suggesting links between these taxa and ice-out conditions. We investigated the distribution and ecology of Aulacoseira pusilla (Meister) Tuji & Houki 2004 in three high-elevation lakes of the U.S. Central Rocky Mountains. Vertical distributions of A. pusilla were quantified every three to four days shortly after the ice-out period for three weeks during July 2017. Populations from two of the lakes were incubated in situ in two experiments to assess the effects of Incubation depth × Nutrient additions and to quantify responses to light. In stratified conditions, the vertical distributions of this species varied spatially and temporally across the three lakes during the study period. There were blooms in the epilimnion of a moderately transparent lake and in deeper waters of a clear lake. Our results suggest that water transparency and its effects on light availability are important when defining relationships between this species and lake thermal conditions. Enhanced understanding of the ecology of A. pusilla will strengthen paleoclimate reconstructions using this species.

Keywords

• Aulacoseira pusilla
• light
• alpine
• lake thermal structure
• diatom autoecology