Kann, J. Aquatic Ecosystem Sciences, LLC, jacobkann@aol.com

 
PROMOTION OF N2 FIXING CYANOBACTERIAL BLOOMS BY LARGE-BODIED DAPHNIA: ALTERNATIVE PATHWAY OF THE TROPHIC CASCADE
 
While the generality of top-down effects on zooplankton communities is well substantiated in the literature, the extension of these effects to the phytoplankton is highly variable. Recent attempts to explain this variability include effects of food quality on the zooplankton themselves, as well as the stoichiometry of zooplankton-regenerated nutrients. With regard to the latter it has been theorized (with support from small-scale experimental data) that because Daphnia recycle nutrients at a high N:P ratio, that subsequent shifts from low to high N:P supply ratios reduces the competitive advantage of N2-fixing cyanobacteria. In contrast to this theory, an analysis performed on a multi-year year data base following the nutrient and plankton dynamics in a shallow, hypereutrophic lake, indicates that high biomass of both large-bodied Daphnia and N2-fixing algae (Aphanizomenon flos-aquae) can coexist, and that in fact Daphnia may contribute to both dominance and biomass of Aphanizomenon. Supply rates favorable to dominance by N2-fixing cyanobacteria were maintained even in the presence of large populations of Daphnia, and a negative correlation was found between Daphnia and the ratio of TIN: SRP. Daphnia's clear suppression of more edible algal competitors, regeneration of TIN and SRP, and apparent enhancement of low TIN:SRP ratios, appeared to contribute to both dominance and biomass of Aphanizomenon.
 
Day: Wednesday, Feb. 3
Time: 04:00 - 04:15pm
Location: Hilton of Santa Fe
 
Code: CS66WE0400H