Native aquatic vegetation establishment in the presence of triploid grass carp

Abstract

Dick GO, Smith DH, Schad AN, Owens CS. 2016. Native aquatic vegetation establishment in the presence of triploid grass carp. Lake Reserv Manage. 32: 222--233.Balancing techniques used to control nuisance aquatic plants while establishing or preserving beneficial vegetation can be complex. Survival and growth of 10 US native aquatic plant species were examined after transplanting into Hydrilla verticillata infested ponds stocked with 4 triploid grass carp (Ctenopharyngodon idella) densities: control (no fish), low (42 fish per vegetated hectare), medium (77), and high (120). Half of the transplants were protected from grass carp herbivory with exclosures. During the first year establishment phase, individual transplants of most species survived within exclosures, but increased mortality was observed for some species without protection. Unprotected Heteranthera dubia, Potamogeton illinoensis, Eleocharis quadrangulata, and Schoenoplectus pungens did not survive the high density treatment. Two-year post-planting coverages of all species combined outside of protected areas averaged 240 m2 in controls, 238 m2 under low density, 179 m2 under medium density, and 109 m2 under high density treatment. Three categories in terms of species' ability to persist in the presence of grass carp were discerned: (1) highly susceptible to herbivory (Heteranthera dubia and Potamogeton illinoensis); (2) susceptible to herbivory but able to establish and spread up to a maximum grass carp density (Vallisneria americana, Eleocharis quadrangulata, Schoenoplectus pungens, and Schoenoplectus tabernaemontani); and (3) established and spread at all grass carp densities (Nymphaea odorata, Echinodorus cordifolius, Justicia americana, and Pontederia cordata). This study demonstrated that restoring native plant communities may be possible when managing nuisance plant species with grass carp and provided insight into species selection to maximize vegetation establishment efforts.