Cyanobacterial picoplankton and its colonial formations in two eutrophic canyon reservoirs (Czech Republic)

Abstract

Autotrophic picoplankton (APP) was studied in a one year cycle in two canyon-type reservoirs in the Czech Republic. APP was present in both reservoirs during the whole year, although in low numbers: In general, picoplankton formed only 0.05-10 % of the total biomass (biovolume, fresh mass). The main proportion was formed by Cyanobacteria (CPP), eucaryotic species played a negligible role. Several morphotypes of CPP were distinguished during the year (April 1998-May 1999): Two rod-shaped Synechococcus species, one spherical type (2 μm diam.) dividing in one plane (Cyanobium), and another spherical type (0.7 μm diam.) dividing in two planes (Synechocystis). During the summer, a proportion of the CPP formed small groups at the beginning, while later the same cell shapes occurred in groups inside of mucilage that corresponded to colonial genera Aphanothece, Cyanodictyon and Aphanocapsa, respectively. Such a life cycle occurred in all the morphotypes except for one (Synechococcus cf. capitatus BAILY-WATTS et KOMAREK). Its appearance and spring maximum in the Slapy reservoir in 1998 was the only evident difference between both reservoirs as far as diversity of CPP morphotypes is concerned. In the year studied, unicellular picoplankton was about two times more abundant in the Slapy reservoir, while the abundance of total picoplankton (unicellular and in colonies) was almost the same in both reservoirs, i.e. about 0.4 million cells maximum and 70-80 10 3 cells/ml average. The fresh mass of the total picoplankton (unicellular + colonial) was larger in the R˙imov reservoir.