Search

Freshwater ecosystems can serve as model systems that reveal insights into biological invasions. In this article, we summarize nine lessons about aquatic invasive species from the North Temperate Lakes Long-Term Ecological Research program and affiliated projects. The lessons about aquatic invasive species are as follows: Invasive species are more widespread than has been documented; they are usually at low abundance; they can irrupt from low-density populations in response to environmental triggers; they can occasionally have enormous and far-reaching impacts; they can affect microbial communities; reservoirs act as invasive species hotspots; ecosystem vulnerability to invasion can be estimated; invasive species removal can produce long-term benefits; and the impacts of invasive species control may be greater than the impacts of the invasive species. This synthesis highlights how long-term research on a freshwater landscape can advance our understanding of invasions. [ABSTRACT FROM AUTHOR]

Species invasions can disrupt aquatic ecosystems by re‐wiring food webs. A trophic cascade triggered by the invasion of the predatory zooplankter spiny water flea (Bythotrephes cederströmii) resulted in increased phytoplankton due to decreased zooplankton grazing. Here, we show that increased phytoplankton biomass led to an increase in lake anoxia. The temporal and spatial extent of anoxia experienced a step change increase coincident with the invasion, and anoxic factor increased by 11 d. Post‐invasion, anoxia established more quickly following spring stratification, driven by an increase in phytoplankton biomass. A shift in spring phytoplankton phenology encompassed both abundance and community composition. Diatoms (Bacillaryophyta) drove the increase in spring phytoplankton biomass, but not all phytoplankton community members increased, shifting the community composition. We infer that increased phytoplankton biomass increased labile organic matter and drove hypolimnetic oxygen consumption. These results demonstrate how a species invasion can shift lake phenology and biogeochemistry. [ABSTRACT FROM AUTHOR]

Although climate change has shifted the phenological timing of plankton in lakes, few studies have explicitly addressed the relative contributions of climate change and other factors, including planktivory and nutrient availability. The spring clear‐water phase is a period of marked reduction in algal biomass and increased water transparency observed in many lakes. Here, we quantified the phenological patterns in the start date, maximum date, duration, and magnitude of the clear‐water phase over 38 yr in Lakes Mendota and Monona, and examined the effects of water temperature, total phosphorus, and food web structure (proportion of large‐bodied Daphnia pulicaria and density of invasive Bythotrephes) and interactions between temperature and other predictors on these clear‐water phase metrics. We found that climate and food web structure affected the clear‐water phase, but the effects differed among the metrics. Higher water temperature led to earlier clear‐water phase start dates and maximum dates in both lakes. The proportion of D. pulicaria affected all clear‐water phase metrics in both lakes. When D. pulicaria proportion was higher, the clear‐water phase occurred earlier, lasted longer, and the water was clearer. Moreover, high Bythotrephes density delayed clear‐water phase start dates (both lakes), and decreased clear‐water phase duration (Lake Mendota) in the following year. These results suggest that variation in food web structure changes the full phenological dynamics of the clear‐water phase, while variation in climate condition affects clear‐water phase timing only. Our findings highlight the importance of large‐bodied grazers for managing water quality under climate change. [ABSTRACT FROM AUTHOR]

Abstract: Cultural eutrophication of lakes due to excess loading of nutrients is a global problem affecting the provisioning of freshwater ecosystem services. Lake water quality is often described by trophic state indicators such as water clarity or concentrations of nutrients, chlorophyll, and cyanobacteria toxins. While these indicators are widely assumed to covary, capturing the same basic aspects of water quality, they can be uncoupled by changes in lake food webs. Outbreak of the invasive predatory zooplankton, Bythotrephes longimanus, in Lakes Mendota and Monona, Wisconsin (U.S.A.) in 2009 led to a decline in the herbivore, Daphnia pulicaria, and in turn, water clarity. We use 20‐yr datasets for Lakes Mendota and Monona to evaluate interactions among nutrients, zooplankton, and phytoplankton that resulted in this trophic cascade. After invasion, diatoms increased in both lakes resulting in reduced water clarity, whereas cyanobacteria did not change in either lake. Multivariate time series analysis revealed that D. pulicaria grazing controlled edible diatoms in both lakes. Cyanobacteria biomass was positively associated with both D. pulicaria and summer nutrient concentrations. These results further clarify the limitations of top‐down control in eutrophic lakes: grazing by zooplankton can control edible phytoplankton taxa, but largely inedible cyanobacteria may be more limited by nutrient concentrations. Accordingly, despite declining clarity in Lake Mendota, the number of beach closures due to cyanobacteria blooms declined following Bythotrephes invasion. Our study reveals how these two indicators of water quality—water clarity and cyanobacteria blooms—can become uncoupled during a food web shift. [ABSTRACT FROM AUTHOR]

Freshwater ecosystems can serve as model systems that reveal insights into biological invasions. In this article, we summarize nine lessons about aquatic invasive species from the North Temperate Lakes Long-Term Ecological Research program and affiliated projects. The lessons about aquatic invasive species are as follows: Invasive species are more widespread than has been documented; they are usually at low abundance; they can irrupt from low-density populations in response to environmental triggers; they can occasionally have enormous and far-reaching impacts; they can affect microbial communities; reservoirs act as invasive species hotspots; ecosystem vulnerability to invasion can be estimated; invasive species removal can produce long-term benefits; and the impacts of invasive species control may be greater than the impacts of the invasive species. This synthesis highlights how long-term research on a freshwater landscape can advance our understanding of invasions., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Institute of Biological Sciences.)