New to the party: non-native cnidarians discovered throughout the Ohio River Basin, USA

The Ponto-Caspian and broader Eurasian region have contributed numerous aquatic invaders to North America, including the infamous zebra mussel (Dreissena polymorpha Pallas, 1771) among many other invertebrates.Contrary to the regular invasion of Eurasian species, few records exist of cnidarians invading freshwater systems.Enter: the often-overlooked colonial benthic cnidarian, Cordylophora caspia (Pallas, 1771).The freshwater hydroid has spread to various parts of the United States including the Great Lakes and Mississippi drainage, with a single observation in 1922 in Benson Creek, Kentucky, a distant tributary of the lower Ohio River.During ichthyoplankton trawls of the Ohio River and tributaries in 2023 and 2024, we collected fragments of hydroid colonies in the bycatch of 38 trawls over 233 river kilometers.Use of DNA barcoding (genes) confirmed two 2023 samples as C. caspia.Briefly, we performed PCR reactions at the 16S and 28S regions to amplify DNA and used Sanger sequencing to produce nucleotide sequences.BLAST queries of these sequences in NCBI GenBank and a maximum-likelihood phylogenetic tree support sample identification as C. caspia.The remaining samples from 2024 closely resembled the genetically identified fragments from 2023.We obtained these samples at multiple points along the mainstem Ohio River, and near the mouths of the Guyandotte, Kanawha, and Scioto Rivers.The presence of C. caspia in the Ohio River and its tributaries could result in competition with native planktivores and sessile organisms and may have both positive and negative influences on other non-native species.A strong potential also exists for negative economic impacts, including biofouling of power plant intakes and water treatment facilities.We recommend future research efforts consider (1) assessment of its current distribution, (2) evaluation of ecological and economic vulnerabilities, and (3) development of effective means to manage this non-native species.