Canadian freshwater mussels and their host associations

Freshwater mussels (order Unionida) are one of the world’s most imperiled taxonomic groups of animals. These mussels have an obligate parasitic larval phase wherein the larva (usually, a glochidium) must attach to a suitable host to complete its metamorphosis into a juvenile mussel. This review synthesizes the current knowledge on the hosts of all 55 species of freshwater mussels in Canada compiled from 264 citations, 70 of which were newly identified by this review. As of October 2023, 827 mussel-host interactions have been documented. The Winged Floater and the Lake Floater currently have no known hosts, with 14 other species having only a single associated evidence type. This review provides an updated library of current knowledge on hosts of Canadian unionids, discusses notable trends in the data, and outlines outstanding knowledge gaps to be addressed in future studies. Relatively few studies aimed at identifying unionid hosts have been conducted in Canadian waters. This lack of understanding of relevant ecological and climatic context has consequences for the development of appropriate conservation actions in Canada.