Original paper

Unicellular and colonial formations of picoplanktonic cyanobacteria under variable environmental conditions and predation pressure

Komárková, Jaroslava; Šimek, Karel

Abstract

Cyanobacterial picoplankton (CPP) and its colonial formations were studied in experiments with assemblages from two ecologically widely different biotopes: eutrophic deep reservoirs in Czech Republic and shallow saline agricultural drainage evaporation pools in San Joaquin Valley, California, USA. Simple experiments with water from both environments were carried out to demonstrate the role of consumers and turbulence in formation and destruction of the CPP many-celled formations.In a picoplankton assemblage submitted to the predation pressure of heterotrophic nanoflagellates (HNF) and of the whole zooplankton assemblage in the experiments with dialysis bags (Rímov Reservoir), spherical solitary living cells were consumed by all predators. Rod-like cells of Synechococcus were not consumed by HNF but by other zooplankton predators. After 4 days of cultivation, solitary cells grouped into secondary "colonies". On the contrary, predation and bioturbation due to the life activity of brine shrimp Artemia franciscana Kellog in the experiments with an assemblage from saline shallow pools (San Joaquin Valley, California) changed the morphospecies composition of picoplankton. All the colonies and simple filaments were either consumed or destroyed rapidly. In these experiments, the rod-like morphotypes (Synechococcus) were most resistant to the predation pressure or bioturbation.The experiments indicated that occurrence of groups and colonies or minute filaments composed of the cells of picocyanobacteria can be conditioned by grazing and/or activity (bioturbation) of predators of different size and consumption capacity. From taxonomical point of view, the experiments have shown that the cyanobacterial genera composed of the cells of picoplanktonic size that are characterized by the formation of colonies, groups and short filaments (e.g. Aphanothece, Aphanocapsa, Cyanodictyon, Pannus, Romeria etc.) have unicellular stages in their life cycle, and on the contrary, that solitary CPP can gather into the groups. The appearance of conglomerates depends on the conditions of the environment such as presence and the type of the predation pressure or bioturbation.

Keywords

picoplanktoncyanobacterialife cyclespredation experiementsmeso-eutrophic reservoirsaline poolsimage analysis