Limnologica, 2009, Vol.39(2), pp.107-114
The zooplankton of oligotrophic lakes in North Patagonia is often dominated by mixotrophic ciliates, particularly and Therefore, we tested whether spp. (i) is an important food for juvenile endemic ( , , , ) and introduced ( ) fish species, and (ii) represents a remarkable grazer of bacteria. Ingestion rates of fish estimated by disappearance of in feeding experiments ranged between 8 ( ) and 53 ( ) ciliates per fish and day, and assimilation rates measured by using radioactively labelled ranged between 3 ( ) and 52 ( ) ciliates per fish and day. However, although we detected the consumption of by fish, the daily consumption amounted to at most 0.2% of the fish biomass which can not cover the energy requirement of the fish. Furthermore, the daily consumption was equivalent to a maximum of 1.6% of the standing stock so that fish predation does not seem to be an important mortality factor for the ciliates. The clearance rate of sp. on natural bacteria was on average 3.8 μl cil h . The daily ingestion (mean 3.9 ng C cil d ) was about 3.5% of the individual biomass of sp. Therefore, bacteria ingestion might explain a ciliate growth rate of appr. 1% d , which was about 17% of the photosynthesis of endosymbiotic algae. The maximum density of sp. in the lake could ingest about 1 μg C L d bacteria which is only 3% of average bacterial production. Thus, grazing by sp. does not seem to be a main loss factor for the bacteria.
Mixotrophic Ciliates ; Stentor ; Fish Predation ; Bacteria ; North Patagonian Lakes ; Oceanography ; Ecology
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