Life cycle size dynamics in Didymosphenia geminata (Bacillariophyceae)

Area of Science:

• Aquatic Ecology
• Microbial Ecology
• Freshwater Biology

Background:

• Didymosphenia geminata (Didymo) is an invasive freshwater alga with significant ecological and economic impacts.
• Understanding its population dynamics, particularly cell size, is crucial for managing its spread.
• Limited knowledge exists on Didymo's population dynamics, size restoration, and reproductive synchronization.

Purpose of the Study:

• To investigate temporal patterns in cell size frequency of Didymosphenia geminata.
• To determine the size restoration strategy employed by Didymo populations.
• To assess the synchronization of life cycles between proximate Didymo populations.

Main Methods:

• Utilized FlowCam technology to measure over 100,000 Didymosphenia geminata cells from two sites in South Boulder Creek, Colorado.
• Applied finite mixture modeling to analyze temporal patterns in cell size distribution.
• Observed size frequency profiles and size diminution in proximate cell nodules.

Main Results:

• Didymosphenia geminata exhibited complex, multimodal size distributions, typically comprising four overlapping age cohorts.
• Conclusive evidence of cell size restoration was documented through abrupt shifts in size distribution.
• Proximate cell nodules displayed asynchronous size frequency profiles and size diminution, indicating spatial heterogeneity.

Conclusions:

• This research provides the first documentation of complex diatom cell size distribution in a lotic system.
• The study confirms cell size restoration as a key process in Didymosphenia geminata populations.
• Variability in size reduction rates at microhabitat scales is highlighted, emphasizing spatial heterogeneity in diatom dynamics.