Poikilothermic organisms accumulate highly unsaturated FA (HUFA) in their lipids at reduced temperatures to maintain cell membrane fluidity. In this study we investigated the effect of temperature on temporal trajectories of FA of fasting Daphnia pulex cultured on a HUFA-free diet. Daphnia pulex populations were maintained for 1 mon at 22 and 11 degrees C and were fed the chlorophyte Ankistrodesmus falcatus. We observed conversion of C18 FA precursors to EPA (20:5n3) and arachidonic acid (ARA; 20:4n6) in D. pulex. We showed that long-term exposure to cold temperature causes a significant increase in EPA. HUFA such as ARA and EPA are highly conserved during starvation. Therefore, D. pulex has the biosynthetic capacity to adjust and to maintain the content of HUFA required to survive at low temperatures.

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UVB (290 nm) tolerance of Daphnia pulex, conditioned to four different food levels (Chlorophyta), was tested under standardized conditions with an artificial radiation source . Parameters measured were survival, percentage of egg bearing Daphnia and the number of juveniles produced after irradiation . LTV-B tolerance of Daphnia pulex was found to be significantly improved with increasing food concentrations at all three parameters . The impact of the four different food concentrations on the photoreactivation system was tested with simultanous UVB and white-light irradiation of Daphnia . Survival rate improved significantly with increasing food levels compared to solely UVB irradiation . Photoreactivation had no effect on the reproductive parameters .

The effects of grazing by captive goslings of the Lesser Snow Goose on coastal vegetation at La Pérouse By. Manitoba were investigated. Swards of Carex subspathacea, Festuca rubra and Calamagrostis deschampsioides were grazed once for different periods (0-180 min) and regrowth of vegetation determined, based on measurements of standing crop, net above-ground primary production (NAPP) and forage quality (leaf nitrogen content). The amounts of foliage removed from swards of Carex subspathacea increased with the length of the grazing period, but after 44 days of regrowth there were no significant differences in above-ground biomass between control and grazed plots. While the amount of foliage removed by goslings from swards of Festuca rubra increased with the length of the grazing period (except after 150 min of grazing), the increase in biomass following defoliation was similar among treatments. Goslings removed little biomass from swards of Calamagrostis deschampsioides, even when the opportunity for grazing was 180 min. No significant differences in standing-crop or NAPP between grazed and ungrazed plots were detected by the end of summer. Grazing had no significant effect on amounts of nitrogen in leaf tissue of all species, suggesting that faecal nitrogen was not rapidly incorporated into plant biomass within the growing season. Patterns of regrowth of these species are compared to that of Puccinellia phryganodes. An increase in goose numbers in recent years has led to birds foraging on less preferred species, such as Calamagrostis deschampsiodes and Festuca rubra. Their poor nutritional quality and a lack of a rapid growth response following defoliation may explain, in part, the decline in the weight of wild goslings recorded over the last decade.

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Survival of transparent and pigmented Daphnia from alpine as well as arctic habitats, exposed to solar radiation with total or reduced UV-B, was measured . In the alpine pond, survivorship and reproduction of transparent juvenile as well as adult Daphnia were significantly reduced due to LTV-B . Transparent adult arctic Daphnia also showed significant reduction in survivorship when exposed to total, when compared with controlled solar radiation . In contrast, heavily melanized adult arctic Daphnia showed no increase in mortality when exposed to natural solar radiation . There appeared to be differences both in tolerance and behavior in the two arctic forms when exposed to solar radiation .

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.