Managing Invasive European Frogbit through Research and Education in New York's Great Lakes Basin:

A Project of the Finger Lakes Institute, Hobart and William Smith Colleges, Cornell University and Cornell Cooperative Extension of Onondaga County

Research and Educational programming is partially funded by the New York Great Lakes Protection Fund Large Grants Program.

European frogbit (Hydrocharis morsus-ranae L.) is an invasive floating plant that has invaded New York’s Great Lakes Basin.  It forms dense floating mats, which have detrimental effects on native aquatic vegetation by blocking light, on animals by reducing food plants and dissolved oxygen, and on human activities by interfering with boating, fishing, swimming, and hunting.  In New York, European frogbit is currently found in southern Lake Ontario, Lake Champlain, Oneida Lake, the St. Lawrence River, and the Hudson River.  It is also established in the states of Michigan (western Lake Erie), Vermont, and Washington, as well as some Canadian provinces (Figure 1).  It poses an imminent threat to other areas, particularly the New York’s Great Lakes Basin as predicted by Zhu et al. (2008).  It is therefore crucial to develop effective management strategies. 

Finger Lakes Institute, Hobart and William Smith Colleges, Cornell University, and Cornell Cooperative Extension of Onondaga County are currently studying the effectiveness of different control methods for European frogbit in order to provide management recommendations to prevent its future spread, and increase public awareness about this invasive species.  Scientists are conducting field and laboratory experiments over a two-year period to evaluate three control methods: 1) hand pulling in low density areas; 2) surface covers for high density areas; and 3) biological controls.  In addition to European frogbit density, we will measure a series of parameters including water chemistry, chlorophyll a concentration, and abundance and diversity of zooplankton, invertebrates, and submerged macrophytes.

Educational Component
An additional component of this project is educational outreach and public awareness. Outreach initiatives to support management efforts include "train the trainer" aquatic plant management workshops, aquatic plant workshops for the general public, a guidance manual for establishing a volunteer watch program, hand pulling demonstrations, multiple public presentations and a web resources.

Visit the project's Educational Outreach Webpage for upcoming public programs!

European frogbit (Hydrocharis morsus-ranae L.) is an invasive plant with extensive impacts in the Northeastern United States and Canada (Mosquin and Whiting 1992). As it continues to establish in the Great Lakes basin and New York State (Zhu et al. 2008), it is likely to have substantial environmental and economic costs. For example, it forms dense floating mats, having detrimental effects on native aquatic vegetation by blocking light, on animals by reducing food plants and dissolved oxygen, and on human commercial and recreational activities by interfering with boating, fishing, swimming, and hunting (Catling et al. 2003). However, direct and indirect management tools have not been vigorously investigated to control this species in the United States with only a few notable exceptions in the states of New York and Michigan (Hart et al. 2000; Langdon 2007). Project objectives are (1) to assess the effectiveness and environmental impacts of several direct control methods, including hand pulling, surface covers, and biological controls, and (2) to encourage better control and prevention through increased public awareness and educational initiatives that includes training workshops, conferences, and web-based resource information that will contribute to the effective management of this plant and other invasive species through early detection and rapid response.

The following field and lab experiments are currently underway as part of this project:

1) Hand pulling for sparse floating plants
Hand pulling has been successful for European frogbit in Britain (Newbold 1975) and other floating plants such as water chestnut (Trapa natans) in New York State (Samuels, personal observation). Hand pulling is labor intensive, but may be effective at a small scale when the invasive has low density. Five sites will be selected in rivers and/or lake bays to study the effectiveness of this method based on the results of an on-going project by Drs. Zhu and Rudstam supported by the NYGLPF Small Grant Program. At each site, different treatments will be applied in three plots (3x3 m2): control (no established European frogbit); untreated (established European frogbit); and treated (established European frogbit, hand pulling). A series of parameters in each plot (details in methodology) will be measured to understand the ecological impacts of European frogbit (contrast between control and untreated plots) and to evaluate the effect of treatments (contrast among all three types of plots). Work will begin in June 2009, sampling will be monthly until August 2009, and be repeated in June 2010 to assess both the seasonal and annual effectiveness of this method.

2) Surface covers for dense beds
Surface covers can be applied at a large scale because they are cost-efficient, less labor intensive, and have less environmental consequences compared to mechanical harvesting, water drawdown, or herbicide applications (Catling et al. 2003). However, they are seldom used for other aquatic plants because the covers can float around and interfere with recreation (NYSDEC 2005). European frogbit is usually present in areas protected from wind and wave action (Catling et al. 2003), which means the covers can be anchored to the shore or in the shallow bottom to not interfere with recreation. Five sites will be chosen for installation of surface covers made of shading cloth that will be secured in the sediment with poles that will remain in place from June - August 2009. The same methods will be applied and the same variables will be measured as in hand pulling.

3) Biological control investigation
With funding support from the NYGLPF Small Grant Program, Drs. Zhu and Rudstam have investigated biological control for European frogbit using snails and are searching for other possible agents. Based on the results of that research, the project will investigate at least two additional agents in the lab as part of this project. Four groups of European frogbit with four different densities of herbivores will be set up in controlled growth chambers for three weeks and the plants will be monitored for the amount of tissue consumed. The final data will be analyzed with ANOVA for comparisons (Kuehl 2000).

The experiments are designed to allow comparisons of the control groups, treated groups, and untreated groups seasonally and annually to evaluate the effectiveness of three control methods and the ecological impacts of European frogbit. In addition to European frogbit density, the following parameters will be measured through hand pulling and surface cover experiments: (1) total phosphorus, soluble reactive phosphorus, total Kjeldahl nitrogen, nitrate/nitrite, and dissolved oxygen in water samples following standard methods (APHA 2000), (2) total phosphorus and organic matter in sediment samples (Wilde et al. 1964), (3) phytoplankton biomass as chlorophyll a concentration at surface and 1 m below surface (Wetzel and Likens 2000), (4) zooplankton species abundance and diversity by triplicate horizontal and vertical hauls (Balcer et al. 1984), (5) epiphytic and benthic invertebrates (Findlay et al. 1989; Peckarsky et al. 1990), and (6) submerged macrophytes (to see if native plants will reemerge, Zhu et al. 2006).

Principal Investigators:

Bin Zhu, Ph.D., Research Scientist, Finger Lakes Institute, Hobart and William Smith Colleges
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Lars Rudstam, Ph.D., Associate Professor, Cornell University Biological Field Station
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Meghan Brown, Ph.D., Assistant Professor, Biology Dept. Hobart and William Smith Colleges
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