Top-down control of phytoplankton by zooplankton in tropical reservoirs in Singapore?

Abstract

The potential for top-down control of phytoplankton populations by zooplankton in tropical lentic systems was examined in 12 shallow reservoirs using a 15 year data set. Regression analyses showed that calanoid, cyclopoid, and rotifer, but not cladoceran, abundances were important in infl uencing the structure of phytoplankton communities. Counts of chlorophytes Ankistrodesmus, Cosmarium and Peridinium decreased with increasing calanoid, cyclopoid and rotifier numbers while populations of thediatoms Melosira and Synedra, Planktotrix and Scenedesmus were inversely correlated with the abundance of calanoid copepods. Cyanobacteria populations, with the exception of Planktotrix, were not negatively affected by increasing zooplankton numbers. This study supports the hypothesis that zooplankton exert 'top-down' control on certain algal communities in tropical lentic systems, however, the use of broad taxonomic groups (calanoids, cyclopoids, cladocerans, and rotifers) potentially masks information on how specific zooplankton exert control on phytoplankton communities. We suggest that a greater taxonomic resolution of the zooplankton fauna is necessary to further understand the complex associations between phytoplankton and zooplankton communities within tropical reservoirs. Nevertheless, even at this coarse scale of investigation, this paper presents clear trends that support the importance of zooplankton in the control of freshwater algal abundance. © National University of Singapore.