Daphnia distribution in Andean- Patagonian lakes: Predation vs. Resource Hypothesis

E BALSEIRO,; BEATRIZ ESTELA MODENUTTI O BEATRIZ MODENUTTI O B. MODENUTTI; CP QUEIMALIÑOS,; MARIANA REISSIG,

Figueiras da Foz

Congreso; Plankton Symposium; 2005

PS

Andean-Patagonian lakes are characterised by their ultraoligotrophic condition, and their small sized zooplankton as many of these deep glacial lakes lack of cladocerans of the genus Daphnia. The distribution of Daphnia was examined under different hypothesis, including visual predation, food resources and sestonic elemental ratio C:P. Eight Andean lakes located between 41ºS and 42º30?S were sampled in a summer season including Nahuel Huapi, Moreno, Correntoso, Espejo, Gutiérrez of Atlantic drainage, and Mascardi, Rivadavia and Futalaufquen of Pacific drainage. The cladoceran assemblage was observed to include two widespread species Bosmina chilensis, B. longirostris and Ceriodaphnia dubia; while Daphnia cf. commutata was restricted to only three lakes. Transparency, seston carbon content, Chl a concentration, particulate P, and presence of different fish species (both exotic and autochthonous) were considered as variables. A predation risk index to visual predation was developed on the basis of the visual capacity of the different fish species present in the lakes. Through a multivariate analysis we were able to explain the Daphnia distribution based on a combination of the predation risk index, water transparency and the C:P ratio.