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

BALSEIRO, E., B. MODENUTTI, C. QUEIMALIÑOS Y M. REISSIG

Figueira da Foz, Portugal

Congreso; Plankton Symposium III; 2005

Food quality in terms of C:P ratio can constrain the success of highly demanding P herbivores as Daphnia. North Andean Patagonian lakes are characterised by their ultraoligotrophic condition, low nutrient concentration and very wide euphotic zones. In these lakes, the distribution of the large Daphnia commutata was analysed in relation with food quality (sestonic C:P ratio) and predation risk. The predation risk was estimated based on the fish species present, relative eye diameter and transparency of the lake. Studied lakes showed high C:P ratios from 350 to >1200. We found that lakes with D. commutata had significantly lower C:P ratio than those without. On the other hand, those lakes where Daphnia is present have the lowest predation risk. In addition, growth experiments with neonates and natural seston of three lakes with different C:P ratio, showed that growth rates were inversely related with C:P of the food. Food quality and Predation Risk combined determine the success or failure of large Daphnia populations in clear ultraoligotrophic lakes.