Sensitivity of vision in high Arctic krill to light and temperature change

A consequence of climate change in Arctic waters coincident with sea ice loss is likely to be an increase in light transmitted through the water column during the polar night. This period of the year, when the sun remains below the horizon throughout the diel cycle, has long been assumed to have minimal biological activity. Yet, recent studies in the high Arctic suggest this is not the case; marine life across the food web is active during this time of the year. Furthermore, light in the polar night fr om both atmospheric (moon, aurora) and in-water (bioluminescence) sources is ecologically significant. This suggests that climate-induced alterations to the underwater light regime in the polar night may alter the winter trophic ecology of high Arctic ma rine environments. This proposal addresses this question by testing the visual performance of an important zooplankton species in high Arctic fjords during winter, the krill Thysanoessa inermis. This species grazes on lower trophic levels, is a vertical migrator, and provides food for fish, birds, and whales. Vision in T. inermis will be studied using an electroretinogram recording approach by visiting researcher Dr. Jonathan Cohen during a 6 week visit to Svalbard. Experiments will evaluate the sensi tivity and speed of the T. inermis eye under increases in light and temperature. It is predicted that the krill eye will be faster and less sensitive under both light and temperature conditions. These results would have implications for krill depth dist ributions given the role of light in diel vertical migration, as well as their ability to capture prey and respond to predators in the polar night. These experiments will allow for temperature and light effects on visual performance to be quantitatively parameterized and therefore included in ongoing modeling efforts attempting to predict ecosystem level effects of warming in the Arctic.