True Metabolizable Energy of Two Southern Aquatic Plants

In order to improve the accuracy of energetic models used to set habitat objectives, estimates of energy availability and metabolizability for a variety of aquatic plants are needed. While true metabolizable energy (TME) values are available for many species of moist-soil seeds, hard mast, agricultural grains, and invertebrates, few TME values exist in the published literature for submersed aquatic vegetation (SAV), despite SAV being a significant food item of many dabbling and diving duck species. Moreover, neither of the two plant species previous analyzed (i.e., shoalgrass [Halodule wrightii], Ballard et al. 2004; widgeon grass [Ruppia maritime], Coluccy et al. 2015) have values near means of other natural foods (Kaminski et al. 2003). Thus, there may exist significant energetic tradeoffs in managing wetland for SAV as opposed to moist-soil or agricultural crops. Moreover, TME values for both native and non-native species such as wild celery (Vallisneria americana) and hydrilla (Hydrilla verticillata) have not been previously published and are needed to assess the value for ducks and the 3 energetic tradeoffs of their control. Orth et al. (2017) suggested that scientists critically evaluate the ecosystem services provided by invasive vs native species before undertaking substantial efforts to manage an invasive. Therefore, we developed the following objectives aimed at estimating the TME of hydrilla for two waterfowl species and providing a comparison native vegetation for ring-necked ducks (Aythya collaris). Objectives 1)Estimate true metabolizable energy of hydrilla shoots and tubers for mallards (Anas platyrhynchos), and 2)Estimate true metabolizable energy of hydrilla and wild celery shoots for ring-necked ducks.