Freshwater mussels are the most imperiled animals in North America according to the US Fish & Wildlife Service. Habitat destruction, pollution, dams, and a litany of other problems have driven many to the verge of extinction. Alas, many are already there. Perhaps the poster children of extinct or soon-to-be-extinct mussels are members of the genus Epioblasma. Once widespread in eastern North America, perhaps no other group has been so decimated by the activities of mankind. And “decimated” is an understatement. Technically, “decimated” means to kill every tenth member of something. For Epioblasma, every species is either extinct or endangered to the point of becoming extinct. And we, mankind, did this to them.
Because so many species of Epioblasma are extinct, the habits of very few have ever been studied. But those that have been investigated reveal a unique (if perhaps somewhat shocking) lifestyle. Like most freshwater mussels, members of Epioblasma have a parasitic larval stage, the glochidium, that uses fishes as hosts. Most mussels have evolved some means of efficiently putting their babies on the proper host. This usually entails luring the host to the mussel to be parasitized. But Epioblasma goes one step further – they actually catch the fish and hold onto it until it has been covered with thousands of parasitic larvae. Mama mussel then releases the host. If all goes as planned, several weeks later the larvae will transform on the fish, fall to the bottom and start their life as juvenile mussels. For the few species for which the hosts are known, the victims are darters and sculpins. The fishes have no one but themselves to blame – they are caught by the mussel when they get too nosy and stick their heads in the mussel to investigate.
Below are some images of the federally endangered Northern Riffleshell and its unfortunate host. Members of the Division of Molluscs have been moving this rare species from the Allegheny River in Pennsylvania to Big Darby Creek in Ohio. The Allegheny population is the only reproducing one on earth but it is doing very well, with probably 100s of thousands of individuals. In partnership with the Columbus Zoo & Aquarium and Columbus Metro Parks, we have been relocating this species for nearly seven years with the permission and funding of the US Fish & Wildlife Service, the ODNR Division of Wildlife, and the Pennsylvania Fish & Boat Commission. To date nearly 10,000 individuals have been moved. In order to monitor these mussels, every one has been affixed with a $4 Passive Integrated Transponder (PIT) tag. All have been released into several of the Metro Parks on Big Darby where they can be protected and monitored. The goal is to start a reproducing population there with the ultimate hope of delisting the species as endangered. This is the largest introduction/augmentation of an endangered species in the history of Ohio.
Next time we will present a gallery of Epioblasma.
About the Author: Dr. G. Thomas Watters is Curator of Molluscs at the Museum of Biological Diversity.