Surface avoidance by freshwater zooplankton: Field evidence on the role of ultraviolet radiation

ALONSO, CRISTINA; ROCCO, VANINA; BARRIGA, JUAN PABLO; BATTINI, MIGUEL ÁNGEL; ZAGARESE, HORACIO

LIMNOLOGY AND OCEANOGRAPHY

American Society of Limnology and Oceanography

Lugar: Alberta; Año: 2004 vol. 49 p. 225 - 232

0024-3590

The avoidance of surface waters by crustacean zooplankton is a common phenomenon both in marine and freshwaters. The contemporary paradigm interprets such behavior as an antipredator strategy. However the phenomenon has also been reported in predator-free environments, which suggests that others variables contribute to this deep-selection behavior. We investigated the possibility that ultraviolet radiation (UVR) could influence the avoidance of surface waters in three interconnected lakes differing in their transparency. Each lake was sampled 17 or 18 times. In the two most transparent lakes, the percentage of the population occurring decreased during spring and summer, but this pattern was not observed in the less transparent lake. Such differences in the patterns of surface-water avoidance were unrelated to the abundance and vertical distribution of the dominant planktivores (early stages of galaxiid fishes) as well as to the temperature and food availability. They were inversely related, however, to the average UVR levels within the surface layer. A UV avoidance strategy was predicted for the copepod Boeckella gracilipes, on account of its low UV tolerance and lack of photoprotective compounds. Our results support this prediction and strongly suggest that surface avoidance by freshwater Patagonian zooplankton is not just a byproduct benefit of an antipredator behavior but is a direct response to high UVR levels.