Trophic Interactions: the Relative Importance of Dreissena Filtration and Daphnia Grazing on Phytoplankton Abundance and Water Clarity

Abstract

A series of controlled laboratory experiments were performed (n=4) to determine the effects of Dreissena filtration and Daphnia grazing on phytoplankton abundance and water clarity. Dreissena consumed significantly more phytoplankton than Daphnia at 48 and 72 hours in vessels containing a single herbivore (Daphnia or Dreissena). Dreissena reduced phytoplankton abundance by 39% overall, while Daphnia reduced 19% of the phytoplankton. However, an additive effect was not observed in vessels containing both herbivores. Phosphorus cycling by Daphnia and cycling and retention by Dreissena changed the dynamics of the vessels significantly. Ultimately, it is likely that Dreissena will increase water clarity to a greater extent than Daphnia due to the differences in phosphorus cycling exhibited by both herbivores.