Shading as a control method for invasive European frogbit (Hydrocharis morsus-ranae L.).

Bin Zhu,Lars G Rudstam,Michael S Ellis,Kelly L Fancher,Shuijin Hu

doi:10.1371/journal.pone.0098488

Abstract

Invasive European frogbit (Hydrocharis morsus-ranae L.) has negative environmental and economic impacts in North American water bodies. It is therefore important to develop effective management tools to control this invasive species. This study investigated shading as a control method for European frogbit in both greenhouse and lake mesocosm experiments. A series of shade treatments (0%, 50%, 60%, 70%, 80%, and 100%) were tested in the greenhouse for three weeks. Results showed that the 100% shade was most effective at controlling European frogbit, and other shade treatments greater than 50% were less effective, reducing frogbit biomass up to 38.2%. There were no differences found in temperature between treatments, but dissolved oxygen decreased as shading increased. A lake mesocosm experiment utilizing 0% shade, 70% shade, and 100% shade treatments was performed in a sheltered inlet of Oneida Lake in New York State for over one month. Resulting European frogbit biomass was significantly (25 times) less in areas treated with the 70% shade and nearly zero with the 100% shade. Shading did not affect temperature but improved DO conditions. Results on the shading effects on submerged macrophytes were not conclusive: no significant differences in changes in species richness and abundance between the three groups at the end of studied period suggested no shading effects; significant differences between the beginning and end communities in the 70% shade and the 100% shade but not in the control group indicated significant impacts of shading. This study is the first one to investigate shading as a control method for European frogbit and it is concluded that a moderately high density shade can effective remove European frogbit likely with minor impacts on the environment. More experiments with larger scales and longer time periods are recommended for further investigation.

Highlights

Biological, physical, and chemical factors all interact to shape the growth, abundance, and distribution of aquatic plants [1,2,3]
The general effect of an increase in light will be positive for aquatic plants, promoting plant growth by increasing photosynthesis [6,7]
Plant growth was evaluated from three different variables: number of plantlets, average biomass per plantlet, and total biomass for all the plantlets in each group

Summary

Introduction

Biological, physical, and chemical factors all interact to shape the growth, abundance, and distribution of aquatic plants [1,2,3]. Important factors affecting aquatic plants include light, depth, fetch, ice scour, latitude, temperature, and water levels. Among these factors, light is of paramount importance, because it exerts a major control on photosynthesis and declines with water depth due to attenuation, scattering, and absorption [4,5]. Zhu et al [8] reported the submerged macrophytes increased their abundance, richness and depths in Oneida Lake, NY when the water clarity increased following the invasion of zebra mussels and nutrient reduction. Extension of submerged plant distribution to deeper depth was observed in bays of the Great Lakes as the water clarity increased [2,9]. Shading as a control method is likely to inhibit growth of invasive aquatic plants

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Methods

Results

Conclusion