Evaluating the Suppression of Hydrilla Verticillata by Manual Removal and Planting Native Aquatic Plants




Maroti, Angela

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Hydrilla is an invasive species found throughout the San Marcos River. There are multiple hydrilla management options however, because of the delicate biodiversity within thisriver system, options are limited. In this study, I examine the ability of the native species, Texas wild rice, water stargrass, and Illinois pondweed to suppress or outcompete hydrilla. In the ex situ study, hydrilla, water stargrass, and Illinois pondweed were planted at varied or equal ratiosin mesocosms, and the biomasses were measured after six weeks. In the in situ study, three sites were selected in the upper section of the San Marcos River. At each site, eight plots with different percentages of hydrilla were removed and five water stargrass and Texas wild rice were planted randomly. The coverage of each plant within the plot was measured monthly for sixmonths and then harvested for biomass. The ex situ studies showed a low root: shoot ratio for hydrilla in the summer compared to the winter and a lower RGR as competition increased. Thisindicates these native plants can successfully suppress or outcompete hydrilla when planted during the winter at higher ratios. In the in situ study there was significantly higher Texas wild rice biomass compared to hydrilla and water stargrass, and less hydrilla cover when ≥ 50% is removed and Texas wild rice is planted, but low Texas wild rice survival. Texas wild rice can compete with hydrilla, if ≥ 50% of hydrilla is removed from a larger area and an increased number of Texas wild rice is planted.


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Hydrilla verticillata, Native aquatic plants, Illinois pondweed



Integrative Biology