Wastewater-algal cultivation systems are a promising way to simultaneously combat multiple environmental problems. In these systems algae use polluting nutrients to grow, thereby cleaning wastewater while producing biomass to be used for biofuel or fertilizer. However, wastewater-algal cultivation has not yet been widely adopted, one reason being that herbivorous zooplankton often proliferate and reduce algal yields. Biological control is a promising solution to this problem, but few studies have tested methods of biological control to improve algal yields. To test whether bluegill sunfish can improve the performance of wastewater-algal cultivation systems, we built 18 225-L raceway ponds with continuous circulation. We filled the ponds with ammonium-rich hypereutrophic media intended to imitate wastewater, inoculated them with local phytoplankton and zooplankton, and performed 12.5% media exchanges every two days to imitate a continuous culturing system. We placed one juvenile bluegill (Lepomis macrochirus) in each of 12 ponds, half inside a 0.1-m² cage meant to reduce predation rates on more mobile prey and half outside the cage. The remaining six ponds served as fishless controls. While placement of fish inside or outside the cage had little effect, after just 18 days the fish had decreased zooplankton mass by 89% and increased dry algal mass by 45%. Our findings demonstrate the potential for hardy zooplanktivorous fish to improve the efficiency of wastewater-algal cultivation, suggesting a strategy for facilitating wider adoption of environmental algal technologies.

Primary Presenter: Chase Rakowski, University of Texas at Austin (chaserak@gmail.com)

Authors:

Chase Rakowski, University of Texas at Austin  ()

Mathew Leibold, University of Florida  ()

Schonna Manning, Florida International University  ()