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Glacier melting and response of Daphnia oxidative stress

We analysed the antioxidant response of Daphnia commutata in an oligotrophic North-Patagonian lake (Lake Mascardi) that receives inputs of glacial clay in one extreme, which creates a plume with a consequent gradient in underwater light intensity (including ultraviolet radiation) and suspended solid material. This gradient in light intensity also affects the light:nutrient ratio and hence the C:P ratio of the food for planktonic herbivores. In the field, along a 9 km transparency gradient, we measured the activities of glutathione S-transferase (GST) and catalase (CAT) enzymes involved in protection against UVR. Through laboratory experiments, we tested the possible role of suspended sediment particles as an additional stressor for a filter feeding zooplankter. Our results indicate that the inputs of glacial clay into the lake have antagonistic effects on Daphnia. Glacial clay was a stress mitigating factor to UVR (decrease in the antioxidant response of GST activity), but was also a source of stress that generated feeding interference, increased respiration rates and consequently increased CAT activity. This light gradient also affected the C:P ratio of food and the maximum response in GST is also modulated by food quality (C:P ratio) that limits its activity in the transparent end of the gradient.