Abstract:
Seasonal changes in abundance of the heterotrophic flagellates
Polytomella sp., rotifers Cephalodella sp., Brachionus caliciflorous and
the testate amoeba Penardochlamys sp. as grazers, cyanophages and
algicidal bacteria as infectious agents on mortality of cyanobacterium,
Microcysis aeruginosa was intensively studied in a hypereutrophic pond
from September to November 2000. Abundance of the rotifers
Cephalodella sp., B. caliciflorous and the Penardochlamys sp. were
relatively high with large fluctuations. The cell density of M. aeruginosa
ranged between 3.0 x 105 to 1.9 X 107 cells ml', where those of algicidal
bacteria were between 0.3 x 12 to 3.7 x 102 PFU ml' and cyanohages were
between 0.9 x 103 to 7.1 X 103 PFU ml". Algicidal bacteria were relatively
high with fluctuation between 0.3 x 104 to 3.7 X 104 PFU mr' and bacterial
peaks were followed with M. aeruginosa peaks. Occasional cyanophages
peaks on 2 and 20 October were followed by sudden collapse of M.
aeruginosa bloom. Percentages of M. aeruginosa cells in food vacuole of
Penardochlamys sp. was high (>77%) during September following
increase of the M. aeruginosa cell density. The flagellate Polytomella sp.
was increased to a peak (2.5 x 105 indi. m') from 10 to 17 November with
decrease of M. aeruginosa cell density. The percentage of B. caluciflorous
individuals ingesting colonies of M. aeruginosa during the bloom period
Mal/age
was significantly high CHest, P<O.Ol). Percentage of testate amoebae
Penardichlamys sp. ingested M. aeruginosa cells was very high (>77%)
during the bloom period. The food vacuoles of Penardichlamys sp.
contained only Microcystis indicating it's specific preference of
Microcystis. The overall results of the study suggest the grazers' protozoa;
Polytomella sp., and the testate amoeba Penardochlamys sp., zooplankton;
Cephalodella sp. and Brachionus caliciflorous, cyanophages and algicidal
bacteria successively involved in suppressing M. aeruginosa bloom in a
freshwater environment.
