Passive transport of a zebra mussel attached to a freshwater fish: A novel Dreissena dispersal mechanism?

Darwin recognized the potential significance of animal-assisted dispersal for the geographic distribution of freshwater species. Phoretic interactions are assumed to contribute to the secondary (post-establishment) spread of invasive freshwater invertebrates, but vertebrate animals reported to disperse invasive bivalves are limited to amphibians and waterfowl. We present evidence of a novel phoretic interaction between the zebra mussel ( Dreissena polymorpha ) and a freshwater cyprinid minnow, the lake chub ( Couesius plumbeus ). To our knowledge, this is the first field-documented case of phoresis involving a freshwater bivalve and a fish. We suggest that this interaction will exacerbate risks of within-basin spread of zebra mussels via fish migration and overland transport of mussels by anglers carrying baitfish from invaded waterbodies.