Biomanipulation: A classic example in a shallow eutrophic pond

Moe Pond, Otsego County, New York, is an artificial impoundment created by the damming of a natural wetland in 1939. It was dominated by blue-green algal blooms between at least 1970-1998. During that time a few scattered clones of sedges (Cyperaceae) along the shoreline were the only vascular plants present. The zooplankton community was dominated by small individuals, primarily rotifers, which were unable to effectively graze the algal community. During this interval, golden shiner (Notemigonus crysoleucas) and brown bullhead (Ictalurus nebulosus) made up the entire fish community. Largemouth and smallmouth bass (Micropterus dolomieu and M. salmoides) were added between 1998 and spring 1999. Golden shiner recruitment functionally ended at that time, and by 2002 they had been virtually eliminated. Secchi transparencies increased and mean chlorophyll a decreased significantly (p<0.05), with algal blooms becoming practically nonexistent. Water weed (Elodea canadensis) now covers the bottom of most of the pond, reaching the surface in many areas up to 2 in in depth. Increased transparency, as well as potential changes in nutrient dynamics, both indirectly brought about by the addition of piscivorous fish, apparently has enabled Elodea to out-compete planktonic algae for available nutrients. This documents a situation where top-down management of the fish community has affected the biota and water quality through trophic cascades. The introduction of piscivorous fish (top-down management) may be used to manage water quality through increased algal grazing by zooplankton. However, a substantial increase in macrophytes, as documented here, may be an outcome.