Long-Term Stability of Macrophyte Dominance Triggered by Common Carp Removal from a Temperate Shallow Lake

Abstract Many ecosystems can abruptly shift between states, and shallow lakes are a classic example. Biomanipulation via the removal of benthivores can shift a shallow lake from a turbid to a clear-water macrophyte-dominated state, but the limited number of long-term studies indicates that persistence in this state rarely lasts beyond 5–10 years. We analyzed 12 years of pre-removal (1996–2007) and 17 years of post-removal (2008–2024) data to assess the ecological impacts of a common carp ( Cyprinus carpio ) removal from Lake Wingra, a shallow eutrophic lake in Madison, Wisconsin, USA. Summer water clarity abruptly increased following the winter 2008 carp removal, resulting in a 64% increase in mean Secchi depth in post-removal summers and a major expansion of the littoral zone. Fast growing submerged macrophytes (for example, Ceratophyllum demersum and invasive Myriophyllum spicatum ) rapidly expanded into deeper zones, reaching the maximum colonization depth of 3.96 m within four summers. Post-removal nutrient concentrations declined by 24–34% and became more correlated with precipitation, suggesting a shift from internal to external regulation of nutrient loading. Three likely interacting mechanisms for maintaining water clarity include predation by centrarchids maintaining low carp populations, the high and stable coverage of submerged macrophytes, and abundant filamentous algae that provide an additional nutrient sink. However, high biomass of invasive species and filamentous algae can degrade ecosystem services and function, and increased variability of precipitation-driven nutrient inputs may destabilize the macrophyte-dominated state in the future. We demonstrate with long-term data the sustained shift of a shallow eutrophic lake out of the turbid state with a single biomanipulation.