Food chain effects of sublethal ultraviolet radiation on subarctic Daphnia pulex – a field and laboratory study

Abstract

In shallow subarctic ponds Daphnia and their algal food are often exposed to solar ultraviolet radiation (UVR). It was previously demonstrated that direct exposure of Daphnia to UVR may result in sublethal damage to Daphnia's intestinal system. This led to the hypothesis that, as consequences of such exposures, Daphnia may be experiencing a situation similar to starvation. We examined, in controlled experiments, the indirect effect of UVR-treated food algae on Daphnia pulex which, themselves, were also exposed to UVR. We specifically tested whether exposure of D. pulex to solar UVR affects food transport and enzymatic digestion. As expected, the UVR-exposed food and UVR-treated Daphnia combination produced the strongest effects on intestinal damage, and mortality. Some of these effects, as well as the grazerrelated effects, were similar to those observed during starvation. The total activities of digestive enzymes (amylase and cellulase) were somewhat reduced in UVR treated D. pulex, but the function of enzymes is not seriously damaged as is clear from the increasing trend of protein-specific activities. We conclude that, in some ways, Daphnia undergoing sublethal UVR exposures may be experiencing a condition similar to what they would experience under very low food or even fasting conditions.

Effects of UVB radiation on grazing of two cladocerans from high-altitude Andean lakes

“…Some metabolic and physiological effects of sub-lethal UV doses on cladoceran species have also been noted, such as decreased/increased respiration rates [73], reduced activities of digestive enzymes, and reduced residence time of algae in the gut [41]. Our study is the first to demonstrate a negative effect of sub-lethal UVB doses on the filtration rate of cladocerans.…”

“…Therefore, it is unlikely that increased UVB doses will affect zooplankton mortality rates dramatically in nature. Sub-lethal damages, on the other hand, are likely more important than lethal effects, and may affect zooplankton in more subtle ways reducing their fitness [24, 25, 41]. …”

UVB Radiation Affects Growth, Reproduction and Tissue Structure of Daphnia magna Across Several Temperatures

“…Zellmer et al. (15) have shown that in D. pulex , UVR exposure can delay the onset of feeding, slow movement of algae through the gut and cause damage to the gut itself. Zellmer et al.…”

“…Despite these protective mechanisms, elevated UVR has been shown to have deleterious effects on survival and reproduction in zooplankters such as Daphnia (10–13). These include direct effects due to DNA disruption (14), organ damage (15,16) and changes in physiology (17), as well as indirect effects such as reduced nutrition and extended exposure to suboptimal temperatures due to longer periods deeper in the water column (18,19).…”

The Effect of Chronic Exposure to Artificial UVB Radiation on the Survival and Reproduction of Daphnia magna Across Two Generations

“…Results from Zellmer et al. (22) showed that UV irradiation damages the gut of Daphnia pulex impeding their ability to assimilate nutrients. The resulting malnourished animals had poorer survival, and although not examined in their study, may have had reduced reproductive output and offspring of lower fitness.…”