For two decades, researchers in masks and with snorkels have plied the silty bottoms of rivers in the southern United States, gathering freshwater mussels by touch. Many shells seemed familiar, but DNA analysis revealed otherwise: before them lay five previously unknown species.
Scientists from the Shedd Aquarium, Arkansas State University and the US Geological Survey have described new species of the genus Obovaria in the rivers of Missouri, Arkansas, Mississippi, Alabama, Louisiana and Texas. The work was published in the journal Zootaxa. Each species is tied to its own river basin and was named after its locality: Obovaria sipseyensis, O. neeskaensis, O. pinetorum, O. tallahattae and O. lumbo.
Identifying mussels by their shells is no easy task: shape changes from headwaters to lower reaches, and males and females differ. That is why genetic analysis of three genes and a comparison of more than four hundred shell outlines played a key role. Each major basin apparently harbors its own genetic lineage.
These mussels are the true filters of rivers. Over its lifetime, a single individual can purify hundreds of thousands of liters of water, removing algae, silt, nutrients and pollutants. They live long, sometimes more than a hundred years, and serve as indicators of water quality. Yet freshwater mussels are the most vulnerable group of animals in North America: about two-thirds of species are under threat.
The main threats are dams, pollution, siltation and invasive species. The mussel life cycle depends on host fish for the larvae, and dams block fish migration. The new species are rare and localized, and therefore require targeted conservation measures. So far, only one of them has been proposed for federal protected status.
The discovery underscores how incomplete our knowledge of river biodiversity is. Without precise species identification, it is impossible to assess extinction risks and organize recovery. As the authors note, we can only protect what we can recognize.
To conserve mussels, it is necessary to study their host fish and to restore populations in laboratories with subsequent return to rivers — this is exactly how several species have already been returned to the wild.
