Vacuolar myelinopathy: waterbird risk on a southeastern impoundment co-infested with Hydrilla verticillata and Aetokthonos hydrillicola

Invasive aquatic plants such as hydrilla (Hydrilla verticillata) are spreading through North America, impeding navigation and hydropower facilities, reducing macrophyte biodiversity, and affecting wildlife health. Managing invasive plants is challenging, especially when the scope of effects to aquatic ecosystems is not fully understood. Hydrilla supports a novel epiphytic cyanobacterium (Aetokthonos hydrillicola) which is implicated in vacuolar myelinopathy (VM) disease. Ingestion of aquatic plants with A. hydrillicola causes often fatal neurological impairment to waterbirds and is transferred from herbivore to predator. We investigated potential VM risk to wildlife species using hydrilla infested sites at a southeastern reservoir and developed a qualitative risk assessment for waterbird species that inhabited the reservoir during fall and early winter. We found that all avian species we observed on the reservoir used hydrilla beds to forage. Seasonal diets of these species exposed them to A. hydrillicola toxin either directly through herbivory, or indirectly through prey with dietary links to hydrilla and the cyanobacteria. Avian and mammalian scavengers are also exposed to the toxin through waterbird carcasses. We present evidence that the current list of species affected by VM is not complete, and further studies are needed to determine the full scope of species vulnerable to VM in lakes and reservoirs with hydrilla and A. hydrillicola.