Population change of invasive Dreissena polymorpha in Douglas Lake from 2003 to 2009.

Abstract

Field observations led us to believe that populations of Dreissena polymorpha in Douglas Lake were decreasing. We hypothesized that this change was caused by environmental changes such as a change in water level, population dynamics including an approach to carrying capacity, or the reduction of resources such as suitable substrate and phytoplankton supply. Our study followed many of the methods of the Galligan (2005) survey for the best comparison between years. Sampling gave a greatly reduced number from the past survey; we found a total of 358 D. polymorpha in which 213 were living. While in 2005, Galligan found a total of 3437 D. polymorpha. Biomass was calculated from this sampling and was compared with phytoplankton densities; however there were no significant results. The survey for D. polymorpha veligers was also inconclusive as it produced only one veliger. The decrease in population may be a result of biotic environmental changes or an approach to carrying capacity but further specific research would have to be done to pinpoint a specific mechanism for this decrease. Our research provides valuable knowledge of an invasive species that could contribute to the eventual control of Dreissena polymorpha by natural means.