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

Abstract

The intensity and spectral composition of visible light are known to influence fish predation on zooplankton. However, in clear-water systems, ultraviolet (UV) radiation (UVR) may also influence fish predation, directly through UV-enhanced foraging, indirectly through alterations in predator-prey overlap, or in a combination of the two. Here we test the hypothesis that UVR facilitates fish predation on zooplankton in an oligotrophic lake. Experiments were conducted in 2.2-m-long UV-transparent or UV-blocking columns suspended in the epilimnion. Zooplankton consumption by young-of-the-year (YOY) largemouth bass (Micropterus salmoides) was compared in the presence and absence of UVR, and the vertical distributions of prey were quantified across light and fish treatments. In addition, a separate experiment was conducted to examine zooplankton vertical responses to UV exposure vs. fish kairomones. Overall, YOY predation on zooplankton was higher in the presence than in the absence of UVR, particularly on diaptomid copepods. This result was only partially explained by zooplankton migratory behaviors, suggesting UV-enhanced searching capabilities in YOY bass. Furthermore, diaptomids displayed a stronger vertical behavioral response to fish kairomones than to UVR whereas Daphnia exhibited a stronger response to UVR.

Toward a more comprehensive theory of zooplankton diel vertical migration: Integrating ultraviolet radiation and water transparency into the biotic paradigm

“…This is warranted to some extent by the importance of Daphnia in pelagic ecosystems in inland waters (Pace 1984;Carpenter et al 1998;Sarnelle 2005), yet other species are likely to be responsive to different selective pressures. For example, in a series of in situ experimental studies in a lake in Pennsylvania, D. catawba responded more strongly to UV than to fish kairomones, while the reverse was true for L. minutus (Leech et al 2009). Smaller species, such as rotifers, will also tend to be less susceptible to visual predators because of their small size.…”

“…In addition, there can also be strong seasonal variation in visual predation pressures due to changes in temperature or production of YOY fish in both marine (Bollens and Frost 1989b;) and freshwater (van Gool and Ringelberg 2002) systems. This is particularly important given that UV may enhance the feeding ability of YOY fish (Leech et al 2009). These seasonal shifts in predation pressure across seasonal transparency gradients may or may not parallel those observed across water bodies of differing transparency.…”

“…For example, the first in situ DVM experiments manipulating solar UV were carried out with Daphnia catawba in 1.5-m-long vertical columns in a lake and showed that D. catawba migrated deeper in the presence of UV than in the absence of UV (Leech and Williamson 2001). In subsequent in situ experiments of a similar design in two lakes of differing transparency, UV stimulated a stronger downward migration in D. catawba than in diaptomid copepods or the cyclopoid copepod Cyclops scutifer in the more transparent lake, while no response to UV was observed in any of the zooplankton in the less transparent lake (Leech et al 2005a). In longerterm field experiments in 8-m-deep mesocosms that were either exposed to or shielded from UV, D. catawba showed a significant downward migration in response to UV, while the copepod L. minutus was more deeply distributed during day than at night but did not show a significant response to UV (Fischer et al 2006).…”

UV wavelengths experienced during development affect larval newt visual sensitivity and predation efficiency

“…By contrast, we found additive, not interactive, effects of the immediate and developmental lighting environment on predation efficiency in newts. Regardless of developmental group, prey survival was higher in the UV2 testing environment, meaning that, as in fishes [2][3][4], the use of UV cues enhances predation efficiency in newt larvae. We also found that UV-deprived larvae foraged less efficiently than larvae reared with UV light.…”

“…When UV cues are not accessible, animals' foraging efficiency is directly negatively affected [2,3]. A recent study demonstrated that, at least in zooplankton predators, UV vision allows location of UV-absorbing food items at greater distances and angles [4].…”