Influence of food resources on body size of Keratella cochlearis (Gosse) in a small Andean Lake.

DIÉGUEZ, MC; MODENUTTI, BE; QUEIMALIÑOS, CP

Collegeville

Simposio; VIIIth Rotifer Symposium; 1997

Morphometry of Keratella cochlearis was analyzed in Laguna Ezquerra, a small lake of South Andes, in relation with food availability. Phytoplankton and zooplankton samples were taken every week during a spring-summer period (October 1988-March 1989). K. cochlearis was present over the entire study, but it was most important in spring (99% of total rotifer density). Phytoplankton was largely (>90%) made up of flagellates, mainly Rhodomonas lacustris and Chrysochromulina parva, except in November when Stichogloea doederleinii and in March when Asterionella formosa were observed. The biovolumen of the algal cells less than 20 um GALD was taken as a measure of the food resources. Significant relationships between temperature and the morphometric parameters: loriga width (LW), loriga length (LL) and total length (TL), were obtained. The maximum variations of the loriga parameters were observed during November-December, in coincidence with the greatest changes in the phytoplankton community. We also found a significant correlation between LL, LW and nanoplankton biovolumen. The observed variation of LL and LW was fitted to an exponential model. The obtained model parameters would indicate that nanoplankton biovolumen fluctuations would drive the rotifer´s population.