How do UV radiation, temperature, and zooplankton influence the dynamics of alpine phytoplankton communities?

Abstract

Plankton in mountain lakes are confronted with generally higher levels of incident ultraviolet radiation (UVR), lower temperatures, and shorter growing seasons than their lower elevation counterparts. The direct inhibitory effects of high UVR and low temperatures on montane phytoplankton are widely recognized. Yet little is known about the indirect effects of these two abiotic factors on phytoplankton, and more specifically whether they alter zooplankton grazing rates which may in turn influence phytoplankton. Here, we report the results of field microcosm experiments that examine the impact of temperature and UVR on phytoplankton growth rates and zooplankton grazing rates (by adult female calanoid copepods). We also examine consequent changes in the absolute and relative abundance of the four dominant phytoplankton species present in the source lake (Asterionella formosa, Dinobryon sp., Discostella stelligera, and Fragilaria crotonensis). All four species exhibited higher growth rates at higher temperatures and three of the four species (all except Dinobryon) exhibited lower growth rates in the presence of UVR versus when shielded from UVR. The in situ grazing rates of zooplankton had significant effects on all species except Asterionella. Lower temperatures significantly reduced grazing rates on Fragilaria and Discostella, but not Dinobryon. While UVR had no effect on zooplankton grazing on any of the four species, there was a significant interaction effect of temperature and UVR on zooplankton grazing on Dinobryon. Discostella and Dinobryon increased in abundance relative to the other species in the presence of UVR. Colder temperatures, the presence of zooplankton, and UVR all had consistently negative effects on rates of increase in overall phytoplankton biomass. These results demonstrate the importance of indirect as well as direct effects of climate forcing by UVR and temperature on phytoplankton community composition in mountain lakes, and suggest that warmer climates and higher UVR levels may favor certain species over others.

No lake left behind: How well do U.S. protected areas meet lake conservation targets?

“…Disproportionate protection of western U.S. lakes suggests that protected lakes are not ecologically representative of continental U.S. lakes. Overrepresentation in the Western Mountains indicates high levels of protection for mountain lakes, which tend to be cold and unproductive (Williamson et al ). These findings are not unique to lakes.…”

Mesocosm Experiments as a Tool for Ecological Climate-Change Research

“…Very few studies have addressed other aspects of climate, such as UV radiation (Williamson et al, 2010), CO 2 enrichment (Andersen et al, 2005), precipitation or water level changes (Bucak et al, 2012;Berger et al, 2007Berger et al, , 2010, and acidification (Christensen et al, 2006), in either isolation or interacting with some of the more obvious aspects (e.g. Christensen et al, 2006;Williamson et al, 2010).…”

Phytoplankton responses to nitrogen enrichment in Pacific Northwest, USA Mountain Lakes

“…Increasing lake temperature (Bergström et al, 2013) and dissolved organic matter concentrations (Daggett et al, 2015) will also increase response magnitude. Other factors, such as light availability, ultraviolet radiation (Williamson et al, 2010), zooplankton grazing (Vinebrooke et al, 2014), or phytoplankton species composition may suppress or mediate response magnitude.…”