INTERACTIONS BETWEEN UV RADIATION AND TEMPERATURE LIMIT INFERENCES FROM SINGLE‐FACTOR EXPERIMENTS¹

Abstract

The global environment is changing. Substantial shifts in temperature, rainfall, cloud cover, and UV radiation (UVR) are all predicted as a result of anthropogenic activity. Although the actual and potential effects of changes in single environmental variables are being studied intensively, the interactive effects of multiple stressors have received little attention. Here we offer the first experimental evidence of interactive effects between UVR and temperature on germination and growth in multicellular organisms. To address the question of how temperature affects survival and growth of organisms in the presence of UVR, we exposed early life stages of two species of intertidal algae, Alaria marginata Postels et Ruprecht and Fucus gardneri Silva, to four levels of UVR at three temperatures for 56 h. PAR and day length (12:12‐h light:dark) were held constant across all treatments. UVR levels bracketed natural levels, and temperatures were within the range of ambient temperatures. Designated endpoints were germination rate and cell number, and we recorded mortality where survival was nil. Our results support the hypothesis that temperature mediates the net biological effect of UVR and vice versa. For instance, spores of A. marginata were able to survive and grow at 15° C at all UV levels and at 10° C in the absence of UVR but were unable to survive at 10° C in the presence of high levels of UVR. Our results suggest that the ability to predict the effects of global change hinges on understanding interactions among environmental variables, imposing strict limits on inferences made from single‐factor experiments.

Interactive effects of temperature and nutrient limitation on the response of alpine phytoplankton growth to ultraviolet radiation

“…A coupled effect of UVR and temperature on phytoplankton growth has been found in cyanobacteria (Roos and Vincent 1998) and in early life stages of intertidal algae (Hoffman et al 2003). While Lotze and Worm (2002) found synergistic effects of nutrient enrichment, grazing, temperature, and UVR exposure on a green macroalga, the complex interaction observed here among UVR, temperature, and nutrients has not been previously documented in phytoplankton.…”

Interactive effects of UV radiation and temperature on microstages of Laminariales (Phaeophyceae) from the Arctic and North Sea

“…from both locations (Table 2). Likewise higher detrimental UV-B effects at lower temperatures were observed in studies with unicellular propagules and sporophytes of red, brown and green algae, regarding recruitment, photosynthetic performance and DNA damage , Gómez et al 2001, Altamirano et al 2003, Hoffmann et al 2003, Rautenberger & Bischof 2006. Whilst UV-Binduced DNA damage appears to be independent of temperature, enzymatic DNA repair is more effective at higher temperatures .…”

Photosynthetic response of Arctic kelp zoospores exposed to radiation and thermal stress

“…[25][26][27][28] There are also reports showing the beneficial effects of increased temperature on the germination rate, cell number, photosynthesis (F v /F m ), and DNA damage repair rates of macroalgae. [29][30][31][32] Zoospore germination in the Arctic population of Alaria esculenta, Laminaria digitata and Saccharina latissima was optimal between 2 and 12 • C, and impaired at 18 • C. 33 Significant additional negative UV-B effect was observed at 2 and 12 • C in L. digitata and at 12 • C in S. latissima, but not in A. esculenta. 33 Whether the temperature optima for photosynthesis are the same or higher than the optimum temperatures for growth (or germination) in different Arctic kelp zoospores is yet to be studied.…”