Impact of fish introduction on planktonic food webs in lakes of the Patagonian Plateau

REISSIG MARIANA, TROCHINE CAROLINA, QUEIMALIÑOS CLAUDIA, BALSEIRO ESTEBAN & MODENUTTI BEATRIZ

BIOLOGICAL CONSERVATION

Elsevier

Año: 2006 vol. 132 p. 437 - 447

0006-3207

Patagonia fishless ponds have been stocked with fishes for recreational purposes sinceearly in the 20th century. We carried out a summer plankton sampling in 18 Patagonianlakes; 12 fishless, 5 with introduced fishes and 1 with endemic fish fauna. The lakes are situatedon a latitudinal gradient from 39 to 49S. Zooplankton and phytoplankton composition,phytoplankton relative abundance, and zooplankton body size and mouthpartmorphology were analyzed. Results showed differences between lakes with and withoutfishes; in the presence of fish zooplankton size spectrum tended to be narrower becauseof the disappearance of Daphnia and large centropagid copepods. Zooplankton compositionchanged: centropagid species richness decreased and rotifers dominated. Contrarily, infishless lakes 3 or 4 centropagid species, differing markedly in body size and exploiting differentfood niches, were observed co-occurring. These changes in zooplankton seemed tocascade down to phytoplankton. Fish introduction increased the phytoplankton similarityin lakes even belonging to different basins in a latitudinal gradient. Indeed, cyanobacteriadominated only in lakes with introduced fishes. Probably the elimination of Daphniafavored cyanobacteria proliferation due to nutrient rebalance. As a consequence, waterquality decreases and the value of sport fisheries is reduced. Fish introduction in Patagoniais a practice that should be re-evaluated by governments and NGOs due to its potentiallynegative impact on lakes and local economies.