LIGHT SPECTRUM IS AN IMPORTANT DETERMINANT OF DIVERSITY AND TROPHIC TRANSFER IN FRESHWATER COMMUNITIES

More than a century of work has shown how light availability influences differences among aquatic communities and drives the dynamics of populations they contain. But even when available, light is not uniform. Light attenuation depends on wavelength, creating wide differences in the spectrum of available light within and among waterbodies. The consequences of this spectral variation has received much less investigation than those of light availability. We sought to experimentally evaluate the potential for light spectrum to influence freshwater communities. In particular, we were interested in how light spectrum altered algal communities, whether the effect of spectrum interacted with phosphorus availability, and whether any effects reverberated up the food web through changes to trophic transfer to zooplankton. We applied four different light spectra to replicate experimental mesocosms containing an algal community derived from relatively high- and low-phosphorus lakes. We crossed light spectrum with phosphorus level to test for interactions with nutrient availability. We then used a growth bioassay with Daphnia to assess trophic transfer to zooplankton. We found that spectrum was an important determinant of both algal diversity and trophic transfer to zooplankton. Algal diversity and composition were also influenced by the interaction between spectrum and phosphorus, whereas trophic transfer to zooplankton was not affected by phosphorus or an interaction. Our results provide new insights into the effect of spectrum on multiple trophic levels in a freshwater food web.

Primary Presenter: Jeff Dudycha, University of South Carolina (dudycha@biol.sc.edu)

Authors:

Jake Swanson, University of Oregon  (swansonjake6@gmail.com)

David Abdulrahman, University of South Carolina  (davidpa@email.sc.edu)

Heather Bruck, University of South Carolina  (hbruck@email.sc.edu)

Tammi Richardson, University of South Carolina  (richardson@biol.sc.edu)

Jeffry Dudycha, University of South Carolina  (dudycha@biol.sc.edu)