Endangered Mussels Gain Ground in Twin Cities Stretch Of Mississippi River
By Phil Delphey
Twin Cities Ecological Services Field Office
The stretch of the Mississippi River that winds through Minnesota's Twin Cities is now home to four federally endangered mussel species. This reach of the river wasn't always a suitable place for these animals.
In the early 20th Century, the river was grossly polluted, with mats of sewage sludge floating on a river that reeked of hydrogen sulfide gas during the summer. The Minneapolis-St. Paul area relied on the river to physically flush away human and industrial waste. This once pristine reach of the river, with ravines and the glorious St. Anthony Falls, had become a sewage canal.
The river's water quality had improved greatly by 2000, thanks to improvements in wastewater treatment. Unfortunately, immense numbers of invasive zebra mussels (Dreissena polymorpha) had begun to smother large, native freshwater mussel beds downstream -- beds too far downstream to have been ravaged by Twin Cities' pollution. Recognizing the impending crisis to the federally endangered Higgins eye pearlymussel (Lampsilis higginsii) and other imperiled mussels, biologists began removing adults from affected beds.
The reach of the Mississippi River through the Twin Cities is upstream of the areas infested by zebra mussels and became a refugia for native mussels. Agency biologists formed the Mussel Coordination Team, and began translocating adult mussels to this and other river reaches. Pooling their skills, knowledge, and energy, the team also investigated mussel propagation techniques that were used over 100 years ago at a state hatchery on the Mississippi River in eastern Iowa.
As a result, five Higgins eye were successfully bred in captivity and then released in 2004. In the following years over 11,000 more juvenile Higgins eye were released, and there is evidence that the original transplants have reproduced. The density and diversity of mussels in the stretch of river that runs through Hidden Falls Park within the Twin Cities metro area is doing so well that it now meets the Service's criteria as a primary habitat area of the utmost importance to Higgins eye recovery.
Additionally, the team reintroduced a small number of endangered winged mapleleaf mussels (Quadrula fragosa), in 2012. These winged mapleleaf represent the return of an endangered species that had been absent from the Mississippi River for a century. The Minnesota Department of Natural Resources has also reintroduced the federally endangered snuffbox (Epioblasma triquetra) and other state-listed species into the river.
Although buoyed by success so far, the future is not without threats. Zebra mussels have been carried by boaters to reaches of the Mississippi River watershed that are upstream of the Twin Cities, and budget restrictions have also cut into propagation activities. The job now is to protect the mussels from growing threats and to continue to find ways to increase the resiliency of these mussel species in light of an uncertain future.