Rayed bean and snuffbox mussels now endangered

The snuffbox is a small, triangular mussel found in small- to medium-sized creeks in areas with a swift current.

The rayed bean is a small mussel, usually less than 1.5 inches long. It lives in smaller, headwater creeks and prefers gravel or sand substrates.

Previously, the rayed bean and snuffbox were both listed on the Michigan endangered species list.

Both species have been found here in Oakland County in the Clinton River Watershed.

Dr. Douglas Hunter, a biologist with Oakland University, looked for both species during a survey he conducted in 2004 with the help of graduate student Debbie Morowski and undergraduate student Luke James.

During that summer, Hunter surveyed 76 sites. His findings showed a decline from the 24 species found in 1978 to 14 in 2004.

He believed that the invasive, non-native zebra mussel impacted the native species, along with watershed urbanization contributing to the decline in species richness.

In his paper, “Freshwater Mussels in the Clinton River, Southeastern Michigan: An Assessment of Community Status,” Hunter wrote that watershed urbanization is “the greater threat in rivers, while (exotic species invasion) is the greater threat in lakes.”

While Hunter and his team found six individual snuffbox mussels, they were unable to find any rayed bean mussels during the survey.

According to the study, Hunter had found the rayed bean at the Cooley Lake Road bridge over the Clinton River back in 1995 and 1996. He still believed the species was present at the site because the rayed bean is difficult to locate. Shells of the rayed bean had been found at that site in 2004, however.

Meanwhile, the Cooley Lake Road Bridge site had a relatively large population of the snuffbox mussel. According to Hunter’s survey and another survey conducted in 1978, the snuffbox had the densest and most stable population of the three endangered mussels in the Clinton River, even though the Cass Lake population had been completely decimated by zebra mussels in the late 1990s.

The U.S. Fish and Wildlife Service added both species to the federal endangered list earlier this month because of a dramatic decline in their populations.

The rayed bean has been eliminated from 73 percent of its historical range, while the snuffbox has disappeared from 62 percent of streams where it has been historically found.

The Wildlife Service is now working with other organizations to develop recovery plans for the mussels and to coordinate efforts to conserve their habitats.