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

Abstract

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 other variables may contribute to this depth-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 in the surface layer 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 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.

Bacterial diversity and morphology in deep ultraoligotrophic Andean lakes: The role of UVR on vertical distribution

“…Andean lakes have extremely transparent waters to UVR, and this factor has been mentioned as responsible for decreases in photosynthetic efficiencies (Modenutti et al 2004), strong photoinhibition (Callieri et al 2007), zooplankton surface avoidance (Alonso et al 2004), and the presence and dominance of species heavily pigmented and UVR resistant (Modenutti et al 2005. In these systems, bacteria would also show consequences of these high irradiances.…”

“…We studied nine Andean lakes characterized by high transparency and high UVR penetration (Morris et al 1995;Balseiro et al 2007) where planktonic organisms, living in the epilimnetic levels of the euphotic zone, are exposed to damaging ultraviolet wavelengths (UVA and UVB) (Alonso et al 2004;Modenutti et al 2004Modenutti et al , 2005. In these lakes, mixotrophic flagellates and ciliates dominate the bacterivorous fraction though in low abundance (Modenutti and Balseiro 2002;Modenutti et al 2005Modenutti et al , 2008.…”

Native and exotic fishes in a Patagonian reservoir with rainbow trout cage culture: spatial and trophic resource use

“…Daphnia, characterized by diel vertical migrations (Alonso et al, 2004;Reissig et al, 2004), was the most evenly consumed item (except for S. trutta), representing the main driver of diet overlap between species. Terrestrial insects were important for littoral dwellers (i.e.…”

UV‐enhanced fish predation and the differential migration of zooplankton to UV radiation and fish

“…In addition, deeper distributions are often more pronounced with increased water clarity (Taylor et al 2000;Mous et al 2004). This could potentially influence predator-prey overlap, as seen by Alonso et al (2004) in UV-transparent lakes in Patagonia, where both the dominant planktivore (i.e., early stages of coldwater galaxiid fishes) and zooplankton prey occupied the deeper pelagic waters during the day. Although they did not quantify it, the authors postulated an increase in predation pressures during periods of increased UV intensity.…”

“…Increased exposure to UVR, particularly UV-B, can lead to deleterious effects on growth, reproduction, and survival of many aquatic organisms, including young-ofthe-year (YOY) fish and their zooplankton prey (Leech and Williamson 2000;Olson et al 2006). Negative phototactic migrations in response to ambient UVR levels have been observed in both zooplankton (Leech and Williamson 2001;Alonso et al 2004;Boeing et al 2004) and fish (Kelly and Bothwell 2002;Ylö nen et al 2005;Holtby and Bothwell 2008), suggesting that behavioral avoidance of UVR has the potential to influence interactions between predator and prey in time and space.…”