Coexistence of two Cyclotella diatom species in the plankton of Lake Baikal

• Published in: Freshwater biology 2015-10, Vol.60 (10), p.2113-2126
• Main Authors: Jewson, David H, Granin, Nick G, Gnatovsky, Ruslan Yu, Lowry, Steve F, Teubner, Katrin
• Format: Article
• Language: English
• Subjects: autumn; Bacillariophyceae; coexistence; Cyclotella; Cyclotella baicalensis; Cyclotella minuta; diatom ecology; environmental factors; field experimentation; Freshwater; ice; interspecific competition; Lake Baikal; phytoplankton; summer; surface temperature
• ISSN: 0046-5070; 1365-2427
• DOI: 10.1111/fwb.12636

In a combined laboratory and field study over 10 years, we investigated how two centric diatom species, Cyclotella baicalensis and Cyclotella minuta, have coexisted in the plankton of Lake Baikal in Siberia for over 100,000 years. The species differ substantially in cell size: C. baicalensis has some of the largest cells found in freshwater phytoplankton at up to 135 μm diameter, but C. minuta can be as small as 10 μm. They illustrate the advantages and disadvantages of small versus large size in a planktonic environment. Other differences included a faster division rate of C. minuta but a faster rate of biovolume increase in C. baicalensis. Timing of their life cycles and peak cell abundances differed. C. baicalensis peaked in June or July after ice break‐up, but C. minuta usually peaked in autumn, because it was able to tolerate higher temperatures and survive higher in the water column during summer stratification, allowing growth to begin earlier than other species. Satellite‐derived surface temperature data combined with temperature tolerances of each species revealed how variation in upwelling affected population development. Speciation may have occurred after a change in environmental conditions allowed larger cells to remain in suspension throughout the year. Long‐term co‐existence became possible because ecological differences reduced interspecific competition.