UV photoprotectants in arctic zooplankton

Abstract

High latitude zooplankton must contend with continuous ultraviolet (UV) exposure in summer, increased UVB fluxes as a result of stratospheric ozone depletion and little UV pro- tection from their transparent waters. In the present study, we evaluated the presence and concen- tration of 4 types of UV-protectants in arctic zooplankton: carotenoids, melanins, scytonemin and mycosporine-like amino acids (MAAs). We analysed 12 commonly occurring crustacean species from 27 freshwater bodies in northern Canada and Alaska. Pigments were detected in all species, and most populations had multiple pigments, suggesting a combination of photoprotection strategies, including broadband screening of UV radiation and carotenoid quenching of reactive oxygen species. Scytonemin, a UVA-screening pigment of cyanobacterial origin that has not been previously detected in zooplankton, was found in 2 crustacean species: the cladoceran Daphnia midden- dorffiana and the fairy shrimp Branchinecta paludosa. MAAs were detected in all populations, pro- viding the first records of high concentrations of these compounds in the genus Daphnia (1 µg mg -1 ) and in the fairy shrimp Artemiopsis stefanssoni (up to 37 µg mg -1 ). Concurrent analyses of food sources showed that scytonemin, carotenoids and MAAs in zooplankton originated in phytoplankton or benthic algal mats. Thus, in addition to providing a measure of UV protection, the pigments also indicate zooplankton food sources and potential benthic-pelagic coupling.