Role of Pigmentation in Zooplankton of Alpine Lakes

Wyoming is unique, with short summers, long cold winters, strong winds and high UV radiation at high elevation. Zooplankton are small animals persisting in the water column of alpine lakes and play an important role in aquatic food webs. To cope with high UV stress zooplankton concentrate large amounts of photoprotective pigments that act as antioxidants, neutralizing dangerous free radicals within body tissues. Zooplankton in alpine lakes display aesthetic colors from almost clear to pink and light orange to deep red depending on pigment type and concentration. Pigmentation is plastic, meaning it varies in response to the environment. Amount of pigments incorporated varies with the presence of visual predators such as fish because pigmentation makes zooplankton more visible prey items. Therefore, zooplankton face a critical trade off: to be pigmented and thus protected from UV, increases the risk of predation yet to be transparent reduces the risk of predation but increases exposure to UV radiation. This tradeoff was thought to be the main driver of pigmentation in alpine zooplankton until 2016 when researchers found vibrant pigmentation under the ice where UV rays cannot penetrate, and visual acuity of predator’s is dampened. They hypothesized that the carotenoid astaxanthin may be used for purposes other than photoprotection such as an antioxidant to prevent fatty acid oxidation when accumulating lipid reserves for winter. For my thesis, I review the literature related to drivers of zooplankton pigmentation and discuss my involvement in field work in a graduate student’s project on pigmentation in alpine zooplankton.