Risk assessment, control, and restoration research on aquatic invasive plant species

Phase II: Impacts of invader removal on native vegetation recovery 

To evaluate the ability of invasive aquatic plant control efforts to yield recovery of native aquatic plant communities, this project will:

  • Perform in-lake invader control experiments using a small-scale in-lake experiment to evaluate how native plants respond to invader removal, seed-addition, light availability, and the combination of these factors
  • Analyze monitoring data from hundreds of lake management projects previously conducted in Minnesota over twenty years
  • Develop a publicly available statewide plant monitoring and management database

Why? Because each year, lake managers, lake associations, municipalities, and the Minnesota Department of Natural Resources manage Eurasian watermilfoil and curly-leaf pondweed in hundreds of Minnesota lakes, principally through herbicide applications. These control efforts are motivated in part by the expectation that reducing invader abundance will restore native macrophyte communities. This “spray-and-pray” approach hinges on the little-tested assumption that it is competition from invaders that has displaced native species. Because aquatic invasive plant management often yields little recovery of native vegetation, we must revisit this assumption. It is crucial to understand when invader reductions do foster recovery of native plants vs. when other limitations may need to be overcome to restore lost diversity.

Phase I

Using applied research on three high-priority aquatic plant species that are invasive or potentially invasive in Minnesota lakes, this research aims to address the need for more guidance and options for controlling these nuisance plants. Species of research include:

  • Nitellopsis obtusa (Starry stonewort), a new invasive alga in Minnesota. Researchers will assess the risk of spread through modeling and will also test how long starry stonewort can remain viable out of water to better understand how best to prevent its spread. Additionally, researchers will conduct laboratory experiments to test the efficacy and selectivity of different herbicides and algaecides. This information is urgently needed during this window of opportunity to minimize impacts of starry stonewort to Minnesota lakes.
  • Myriophyllum spicatum (Eurasian watermilfoil) and Potamogeton crispus (curly-leaf pondweed), both of which have been in Minnesota for several decades and are now found in hundreds of lakes throughout the state. Although both of these species have been a focus of management and research for several years, there are still limits in our ability to effectively control these species and to support the post-control recovery of native plant species. Researchers will analyze existing datasets, perform new field work, and develop a citizen-science monitoring program to improve understanding of factors that drive invasion of these species and that influence the effectiveness of management efforts.

Collectively, this research will aim to create biologically and economically sound solutions to prevent and control these invasive plants and to disseminate scientific information that assists the DNR, watershed districts, lake associations, and citizen groups around the state with management strategies. Aquatic invasive plants are a major threat to Minnesota’s lakes, rivers, and wetlands. Aquatic invasive plants can form dense mats on the water’s surface, reducing space and light available to other plant species. This can lower native plant diversity, reduce habitat quality for fish and other animals, and change the way lakes function. They can also interfere with boating, recreation, and other human uses.


As of January 2019, researchers are continuing to conduct laboratory experiments testing the effectiveness of different algaecides/herbicides being used for starry stonewort treatments that have not been subject to rigorous evaluation through published, peer-reviewed experiments. Researchers are now acquiring and synthesizing monitoring data from statewide treatments for Eurasian watermilfoil and curly-leaf pondweed. For both of these species, we have made substantial progress on in-lake removal experiments to determine the extent to which control of these AIS is sufficient to foster recovery of native aquatic plant communities or whether additional management interventions are needed to restore native vegetation.

Laboratory experiments to test the effectiveness of different algaecides/herbicides on starry stonewort had been initiated as of July 2018. Field sampling is ongoing to evaluate outcomes of starry stonewort control efforts in lakes. Data from statewide treatments of Eurasian watermilfoil and curly-leaf pondweed have been acquired and are currently being synthesized. For both species, researchers have also initiated in-lake removal experiments to determine whether effective control of these AIS is sufficient to support recovery of native aquatic plant communities or whether additional management strategies (e.g., water quality improvement, native plant seed addition) are needed to restore native aquatic vegetation. 

Ecological niche modeling has been completed for starry stonewort, using occurrence data from 8 countries, 19 climate variables, and remotely sensed environmental data to characterize the environmental niches occupied by starry stonewort in its native and invaded ranges. Initial findings indicate that starry stonewort has expanded into regions of the U.S. with climate conditions distinct from those found in its native range. Roughly one-third of Minnesota appears to constitute suitable habitat for starry stonewort, as do large portions of the Intermountain West, Great Plains, and Mid-Atlantic — areas with no known occurrences to date. Next, researchers will scale down risk assessment to individual lakes within Minnesota. Lakes identified as high-risk will be recommended for targeted surveillance by the AIS Detectors program.

Final outcomes:

We conducted research to predict invasion risk, assess ecological impacts, evaluate control efficacy, and investigate factors limiting post-control recovery of native aquatic plants. This work was applied to three target species at different stages of invasion: (1) Nitellopsis obtusa (starry stonewort), first found in Minnesota in 2015 and now known in 14 lakes; (2) Myriophyllum spicatum (Eurasian watermilfoil), found in 1987 and established in >300 lakes; and (3) Potamogeton crispus (curly-leaf pondweed), here for >100 years and in >750 lakes. For starry stonewort, we developed models to predict risk of further spread and prioritize search locations for statewide volunteer search efforts, experiments to determine how long starry stonewort remains can survive out of water (i.e., remain transportable by boaters), and field and lab-based control experiments to guide management. For Eurasian watermilfoil and curly-leaf pondweed, we investigated relationships with native plant biodiversity, finding that they displace native species, an effect compounded by lower water clarity, and contribute to “biotic homogenization”—loss of ecological distinctiveness. We are investigating how to better control these invasive species and foster recovery of native vegetation by synthesizing thousands of aquatic plant surveys and management records collected in Minnesota and by conducting in-lake removal and restoration experiments. This work will continue under Phase II, above.

Phase II

Project manager: Dan Larkin

Funded by: Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources

Project start date: 2019

Estimated project end date: 2021


Phase I

Project manager: Dan Larkin

Funded by: Environment and Natural Resources Trust Fund as recommended by the Legislative-Citizen Commission on Minnesota Resources

Project start date: 2015

Project end date: 2019