Long-term changes in pigmentation of arctic Daphnia provide potential for reconstructing aquatic UV exposure Liisa Nevalainen a, b, * , Marttiina V. Rantala c , Tomi P. Luoto a, c , Antti E.K. Ojala d , Milla Rautio e a University of Jyv€ askyl€ a, Department of Biological and Environmental Science, P.O. Box 35, 40014 Jyv€ askyl€ a, Finland b University of Helsinki, Department of Environmental Sciences, Niemenkatu 73, 15140 Lahti, Finland c University of Helsinki, Department of Geosciences and Geography, P.O. Box 64, 00014 Helsinki, Finland d Geological Survey of Finland, Betonimiehenkuja 4, 02150 Espoo, Finland e Universit e du Qu ebec  a Chicoutimi, D epartement des Sciences Fondamentales, Centre for Northern Studies (CEN) and Groupe de Recherche Interuniversitaire en Limnologie (GRIL), 555 boulevard de l’Universit e, Chicoutimi, Qu ebec G7H 2B1, Canada article info Article history: Received 23 March 2016 Received in revised form 17 May 2016 Accepted 17 May 2016 Keywords: Arctic lakes Fossil pigments Paleolimnology UV radiation Zooplankton abstract Despite the biologically damaging impacts of solar ultraviolet radiation (UV) in nature, little is known about its natural variability, forcing mechanisms, and long-term effects on ecosystems and organisms. Arctic zooplankton, for example the aquatic keystone genus Daphnia (Crustacea, Cladocera) responds to biologically damaging UV by utilizing photoprotective strategies, including pigmentation. We examined the preservation and content of UV-screening pigments in fossil Daphnia remains (ephippia) in two arctic lake sediment cores from Cornwallis Island (Lake R1), Canada, and Spitsbergen (Lake Fugledammen), Svalbard. The aims were to document changes in the degree of UV-protective pigmentation throughout the past centuries, elucidate the adaptive responses of zooplankton to long-term variations in UV exposure, and estimate the potential of fossil zooplankton pigments in reconstructing aquatic UV re- gimes. The spectroscopic absorbance measurements of fossil Daphnia ephippia under UV (280e400 nm) and visible light (400e700 nm) spectral ranges indicated that melanin (absorbance maxima at UV wavebands 280e350 nm) and carotenoids (absorbance maxima at 400e450 nm) pigments were pre- served in the ephippia in both sediment cores. Downcore measurements of the most important UV- protective pigment melanin (absorbance measured at 305 and 340 nm) showed marked long-term variations in the degree of melanisation. These variations likely represented long-term trends in aquatic UV exposure and were positively related with solar radiation intensity. The corresponding trends in melanisation and solar activity were disrupted at the turn of the 20th century in R1, but remained as strong in Fugledammen. The reversed trends in the R1 core were simultaneous with a significant aquatic community reorganization taking place in the lake, suggesting that recent environmental changes, likely related to climate warming had a local effect on pigmentation strategies. This time horizon is also concurrent with previously recorded major ecological shifts in circumpolar lakes when human induced changes in ecological processes of sensitive arctic ecosystems started to occur. The current centennial record of UV-induced melanisation of sedimentary Daphnia ephippia presents unique reference material for assessing UV impacts in arctic aquatic ecosystems before human influence and during the 20th century climate change and provides potential for assessing past aquatic UV regimes. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction UV radiation (UV), the highly energetic waveband (280e400 nm) of solar irradiance, poses a significant threats to sensitive high latitude aquatic ecosystems, since it has many bio- logically deleterious effects. High underwater UV results in changes in productivity and species composition, and it ultimately alters * Corresponding author. University of Jyv€ askyl€ a, Department of Biological and Environmental Science, P.O. Box 35, 40014, Jyv€ askyl€ a, Finland. E-mail addresses: liisa.e.nevalainen@jyu.fi (L. Nevalainen), marttiina.rantala@ helsinki.fi (M.V. Rantala), tomi.luoto@helsinki.fi (T.P. Luoto), antti.ojala@gtk.fi (A.E.K. Ojala), milla.rautio@uqac.ca (M. Rautio). Contents lists available at ScienceDirect Quaternary Science Reviews journal homepage: www.elsevier.com/locate/quascirev http://dx.doi.org/10.1016/j.quascirev.2016.05.022 0277-3791/© 2016 Elsevier Ltd. All rights reserved. Quaternary Science Reviews 144 (2016) 44e50