The Effects of Alewife on the Zooplankton Community in Townhouse Pond

The purpose of this study was to determine what plankton species was more dominant in Townhouse Pond and what effects predation has on the food web. Plankton size is important when determining pelagic food web structure. Plankton size along with predation determines whether the lake is dominated by top-down or bottom-up control. Plankton size and biomass, grazing rates, light intensity, and chemistry parameters were all determined for Townhouse Pond in October 2008. We concluded that Townhouse Pond is a mesotrophic lake and is mainly dominated by phytoplankton, such as Microystis and Dinobryon. Alewife (Alosa pseudoharengus), planktivorous fish, are dominant in this pond resulting in top-down control. Although various studies were conducted here, further research could determine the abundance of alewife and their prey and specific parameter that effect their predation. Acknowledgements: I would like to thank the Field Limnology class for helping collect all of the data in the field and reviewing my first draft. I would like to thank our teaching assistants, Francoise Morison and Amanda Murby, for helping with the creation of the graphs and analyzing the data. Also, I would like to thank Amanda and Francoise for extracting chlorophyll a and plankton biomass. I would like to thank Dr. Jim Haney and Dr. Al Baker for helping with the collection of the data, identification of zooplankton and phytoplankton, and analyzing the data. Finally, I would like to thank the Lakes Lay Monitoring Lab for conducting the analysis of phosphorous. Thank you everyone for all of your help. Introduction: The effects of alewife on size distribution in Townhouse Pond are relatively unknown. Townhouse Pond is currently a mesotrophic lake with moderate nutrient levels and productivity. However, the effects of plankton alone are widely studied. If concentrations are not properly monitored and managed, the nutrient levels and plankton abundance will continue to increase, resulting in health risks for both humans and animals which are great concerns to the neighboring population. Plankton size is used to understand ecological and physiological behavior, including nutrient uptake, sinking rates and vertical light gradient (Naselli-Flores, Luigi, Meric, 2007). In addition, plankton size can be used for taxonomic and UNH Center Freshwat. Biol. Res. 11(1): 1-8 (2009) phylogenetic classifications along with natural selection and monitoring of water quality (Naselli-Flores, Luigi, Meric, 2007). Size determines environmental conditions, such as seasonal patterns, disturbances and perturbations caused by algal blooms (Naselli-Flores, Luigi, Meric, 2007). More importantly, plankton size can be used to determine grazing behaviors among zooplankton, phytoplankton and planktivores. The size efficiency hypothesis by Dodson and Brooks (1965) is an important guide to understanding the effects of predation on different size fractions. The size efficiency hypothesis states that larger zooplankton( >2.0 mm), such as Daphnia, are more efficient grazers. When predation by planktivorous fish is low the system is dominated by large zooplankton, which graze on the smaller zooplankton (<2.0 mm). When predation is high from planktivorous fish the large zooplankton are eliminated, allowing the small zooplankton to dominate. When predation is moderate there are equal populations of small and large zooplankton along with planktivorous fish. (Brooks & Dodson, 1965) Another important factor in determining the effect of predation is whether the system is controlled by top-down or bottom-up effects. Top-down control occurs when there is an efficient predator and the mortality due to intraspecific competition is constant (Devaraj 2004). Bottom-up control occurs when there are inefficient predators