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Revista chilena de historia natural

Print version ISSN 0716-078X


BALSEIRO, ESTEBAN G.; QUEIMALINOS, CLAUDIA P.  and  MODENUTTI, BEATRIZ E.. Grazing impact on autotrophic picoplankton in two south Andean lakes (Patagonia, Argentina) with different light:nutrient ratios. Rev. chil. hist. nat. [online]. 2004, vol.77, n.1, pp.73-85. ISSN 0716-078X.

Andean ultraoligotrophic lakes are environments with high light:nutrient ratios. In these lakes a particular planktonic food web has been noticed, constituted by large mixotrophic ciliates which share and compete for food resources with nanoflagellates and cladocerans. Clearance rates on autotrophic picoplankton of nanoflagellates, the ciliate Ophrydium naumanni and cladocerans were compared through grazing experiments in lakes Moreno Oeste and Rivadavia. The lakes exhibited significant differences in the light:nutrient ratio and had different crustacean and zooplankton compositions. In lake Moreno Oeste the metalimnion was included in the euphotic zone resulting in an illuminated layer where deep chlorophyll maxima developed. On the contrary, in lake Rivadavia the illuminated layers were restricted to the epilimnion and no deep chlorophyll maxima were observed. In lake Moreno Oeste, the contribution to total bacterivory of the ciliate O. naumanni and the cladoceran Ceriodaphnia dubia was observed to increase at 30 m depth, due mainly to the vertical distribution of both species. On the contrary, the grazing rates of the nanoflagellate assemblage, dominated by the mixotrophic Chrysochromulina parva, did not change along the water column and were considerably high (one order of magnitude higher than those obtained for O. naumanni and C. dubia). In lake Rivadavia, nanoflagellate grazing rates were lower and the relative impact of the nanoflagellate assemblage was comparable to those of O. naumanni and Daphnia cf .commutata. The observed difference in clearance rates of the nanoflagellate assemblage probably would reflect an increase in the phagotrophy where light energy is higher relative to phosphorus. In lake Moreno Oeste where light is not limiting, the observed increase of the phagotrophy by protists may be due to a higher requirement of limiting elements

Keywords : planktonic bacterivory; ultraoligotrophic lakes; mixotrophy; light:nutrient ratio; Ophrydium naumanni; nanoflagellates.

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