Cyanobacterial dominance: The role of buoyancy regulation in dynamic lake environments

Murray-Darling Freshwater Research Centre

MDFRC item.

The interactions of size, shape, and density of cyanobacteria result in a 5-order of magnitude difference in flotation or sinking rates which, in turn, influence the extent of their dispersion in turbulent water masses. Active mixing through resource-replete waters of high clarity favours fast-growing, small-celled species. Where photosynthetically active radiation is severely attenuated through the wind-mixed layer, species may rely on turbulent entrainment but must be adapted toward efficient light harvesting (morphological attenuation, enhanced pigmentation). In both strongly segregated waters (light- and nutrient-rich layers separated vertically) and waters experiencing high-frequency fluctuations in vertical mixing and optical depth, emphasis is placed on the ability to make rapid, buoyancy-adjusted vertical movements, favoured by large size. The cyanobacterial 1ife-forms respectively typical of these contrasted limnological systems — unicellular coccoids (e.g., Synechococcus), solitary filaments (e.g., Oscillatoria) and colonial forms (e.g., Microcystis) — illustrate the diversity of evolutionary adaptations to be discerned among the planktonic cyanobacteria and which contributes to their reputation as a prominent and successful group of organisms.