Expansion of <i>Hydrilla verticillata</i> L. f. Royle within the Monongahela River system and associated invasive submerged aquatic vegetation

Abstract Submerged aquatic vegetation (SAV) is often under-documented at the species level in routine monitoring and regulatory assessments, where vegetation is commonly recorded without species-level identification (Personal Communication, Department of Environmental Protection and the Pennsylvania Fish and Boat Commission). Here, we present a summary of existing records and field collections made in the Pennsylvania portion of Monongahela River system. Our findings suggest that the dominant SAV in this river is Hydrilla ( Hydrilla verticillata L. f. Royle), one of the most aggressive invasive macrophytes in North America. Further, our recent collections indicate the presence of other invasives: Eurasian Watermilfoil ( Myriophyllum spicatum L.) and Curlyleaf Pondweed ( Potamogeton crispus L.). Native species such as Coontail (Ceratophyllum demersum L.) and Vallisneria (Vallisneria americana Michx.) were present but not prominent in sampled locations. The documentation of H. verticillata and other non-native invasive SAV species suggests that the Monongahela River is now hosting an invasive epidemic, one that may have widespread ecological implications.