Theoretical and Experimental Ecology

Collaborators – Yesim Buyukates

Graduate Students – George Gable, Carrie Miller, Hsiu-Ping Li

Influence of pulsed inflows and nutrient loading on zooplankton and phytoplankton community structure and biomass in microcosm experiments using estuarine assemblages

Productivity and community structure of phytoplankton and zooplankton are influenced by hydrologic disturbances in many ways. In a recent modeling study it was suggested that pulsed inflows might enhance zooplankton performance, curb accumulation of phytoplankton accumulated biomass, and promote phytoplankton species diversity. We tested these predictions by performing multiple microcosm experiments on natural plankton assemblages. Experiments of semi-continuous and flow-through design were conducted. We investigated the effect of two different inflow and nutrient loading regimes on zooplankton biomass, and phytoplankton biomass and diversity, i.e., continuous and pulsed inflows of 3-day frequency. Despite differences in initial community structure between experiments, as well as the very different communities that arose between experimental designs, our findings showed that pulsed inflows altered plankton dynamics. In all cases, pulsed inflows resulted in greater zooplankton biomass. And in all but one experiment, pulsed inflows resulted in lower phytoplankton biomass and higher diversity. We speculate that greater phytoplankton diversity in the pulsed flow treatments favored selectively feeding zooplankton, whose better performance prevented higher accumulation of phytoplankton biomass.

Directing the Fall of Darwin’s “Grain in the Balance”: Manipulation of Hydraulic Flushing as a Potential Control of Phytoplankton Population Dynamics

Foodweb interactions, such as competition for limiting resources, are inherently non-linear. Consequently, they can give rise to chaotic, or undeterminable, population dynamics. Population dynamics are not always undeterminable, however, sometimes they are quite predictable. What conditions cause one behavior to prevail over the other? Here we focus on aquatic environments, specifically plankton ecosystems, and show numerically and experimentally that when the magnitude and periodicity of hydraulic flushing and nutrient loading are large chaotic behavior, as described by chaos theory, is replaced by determinable dynamics. In other words, the system only responded to manipulation in a predictable manner when the disturbance to the system was large. It may be that management efforts aimed at maintaining ecosystem health in aquatic systems, e.g., enhancing biodiversity, controlling eutrophication, preventing harmful algal blooms, etc., may require large-scale, controlled manipulations of flushing periodicity and magnitude.