Dynamics of Cladocera and Rotifera species in a polymictic lake (lake 3rd order) in Southern South America

GONZALEZ SAGRARIO, M. A. AND A. H. ESCALANTE

Santa Fe, USA

Congreso; ASLO, 1999 Aquatic Sciences Meeting; 1999

American Society of Limnology and Oceanography

Qualitative and quantitative analysis of zooplankton structure was surveyed in “Los Padres “ pond, Argentina, during June 1997-June 1998. Three sampling stations were selected. St. 1: open waters in mid-pond (1.24 mean depth); St.2: at “Los Padres” creek incoming and St.3: in front of a small dam. Monthly subsuperficial samples were taken in each station, filtering one hundred liters thorough a 35 um mesh net. To determine densities, 1 ml aliquots in Sedgwick-Rafter chambers were counted. Nineteen species of Cladocera and thirty two of Rotifera were registered. Bosmina (Neobosmina) huaronensis and Ceriodaphnia dubia occurred during the whole annual cycle in high densities at St.1 and St. 3. However, different rotifer species were dominant throughout the period at St. 2. Peaks of 1158.7 and 2902.5 ind/l at St.1 and St3, respectively, were due to Bosmina (N.)  huaronensis during spring. As rotifers concerns, Brachionus calyciflorus predominated in winter (up to 206 ind./l) whereas Filinia longiseta and Trichocerca sp. reached values of 187 and 278 ind/l in summer, respectively. Zooplankton structure at St. 1 and St. 3 suggest similar lenitic conditions. St.2, instead, is hardly influences by “Los Padres” Creek, showing a fluctuating community structure.