Ciliate community structure in two South Andes lakes: The effect of lake water on Ophrydium naumanni distribution.

BEATRIZ ESTELA MODENUTTI; E BALSEIRO,; CLAUDIA QUEIMALIÑOS,

AQUATIC MICROBIAL ECOLOGY

INTER-RESEARCH

Año: 2000 vol. 21 p. 299 - 307

0948-3055

ABSTRACT: Planktonic ciliates were examined during a spring-summer period (November 1998 toApril 1999) in 2 South Andean lakes in Argentina, with different dissolved organic carbon (DOC) andnutrient concentrations. Lake Moreno Oeste is a deep warm monomictic lake (Zmax9=0 m), while LakeMorenito is shallower (Zmax= 12 m) and polymictic. Sampling was performed in a mid-lake station,where vertical profiles of temperature, light, and chlorophyll a concentration were measured in situ. Inaddition, DOC and phosphorus concentrations were determined, and samples for bacteria, phytoplanktonand ciliate enumeration were taken along the water columns. Lake Morenito presented DOCand phosphorus concentrations 3-fold higher than those of Lake Moreno Oeste. Two different ciliateassemblages were present. Lake Moreno Oeste was dominated by the large mixotrophic ciliate Ophrydiumnaumanni, which was absent in Lake Morenito. In order to test 0. naumanni water dependence,a series of laboratory experiments were performed during the sampling season. The experiments consistedof the incubation of the ciliate in filtered water from both lakes and the subsequent analysis ofgrowth rates in each treatment. In addition, experiments with Moreno Oeste lake water with a 4-foldincreased phosphorus concentration (addition of MBL culture medium) were conducted. The incubationof 0. naumanni in Lake Morenito water led to highly negative growth rates of the ciliate. Resultsshowed that the addition of nutrients did not cause significant differences in the growth rates.