Cryptic invaders: nonindigenous and cryptogenic freshwater Bryozoa and Entoprocta in the St. Lawrence River

Abstract

The distributions of most cosmopolitan invertebrate species are assumed to result from natural processes. Cryptic invertebrates with obscure biogeographic origins are often considered native by default, resulting in potentially severe underestimation of the extent of human-assisted invasions. This problem is exemplified by freshwater Bryozoa (Ectoprocta) and Entoprocta—small and widely distributed invertebrates commonly found in lakes and rivers. A benthic survey of a thermally modified section of the St. Lawrence River revealed the presence of two nonindigenous bryozoans: Carter’s moss animal Lophopodella carteri (Hyatt) and the crystal moss animal Lophopus crystallinus Pallas. Also discovered was a cryptogenic entoproct, the goblet worm Urnatella gracilis Leidy. These species were collected as statoblasts and (in the case of U. gracilis) colonial fragments downstream of the Gentilly-2 nuclear power plant at Bécancoeur, Quebec. Local densities of both U. gracilis and L. carteri increased by an order of magnitude at sites closer to the power plant. The occurrence of Lophopus crystallinus statoblasts in St. Lawrence River sediments is the first documented physical evidence of the species in North America. Contrary to the presumed natural Holarctic distribution of L. crystallinus, our literature review found that published historical records of L. crystallinus in the United States are erroneous or unsubstantiated. We propose that L. crystallinus is a western Palearctic species recently introduced to the St. Lawrence River, most likely as statoblasts discharged with ballast water from transoceanic ships.