Quantifying the Outcomes of a Century-Old Invasion: The Impacts of Common Carp on Lakes Across Three Temperate Ecoregions in North America

Biological invasions are projected to be the main driver of biodiversity loss in lakes in the 21^st century. To provide insights into what the impacts of current invaders might be in the future we quantified the outcomes of an invasion that occurred a century ago, the introduction of common carp to North America. We use the decline in aquatic vegetation density and diversity as an index of ecological impact across three temperate ecoregions. Using whole lake manipulations we demonstrate that carp biomass of 150 and 280 kg/ha causes a decline in aquatic vegetation cover to 30% and 10%, respectively, a moderate and severe impact. These biomass levels were represented by gillnet catch rates of 0.74, and 3.33 kg/net, respectively. By analyzing gillnet catch rates in 500+ lakes we estimate that carp has had a moderate or severe impact on 71.2%, and 45.7% of Great Plains lakes, respectively, and 18.7%, and 4% of Temperate Forrest lakes, respectively. No lakes were impacted across the Northern Forest ecoregion. Our study suggests that a century-old invasion of common carp may be responsible for the loss of aquatic macrophyte cover and diversity in most Great Plains lakes and a large proportion of Temperate Forest lakes.