· A Refuge from Ice
· Special Features
· Did You Know?
· Wild Side
· Cause for Concern
· Looking Ahead

Global 200 Snapshot

The Mississippi Piedmont Rivers and Streams ecoregion is the richest freshwater system of its kind in the world. It is recognized as having greater diversity of mussels, crayfish, salamanders, and freshwater fish than anywhere else in the world, with a comparable climate.  

A Refuge from Ice

The diversity of habitats, age, favorable climate, and geologic stability of the region, along with its escape from glaciation during the last Ice Age, have promoted the evolution of a high diversity of animals. When much of North America was covered in ice, this region remained unglaciated and a refuge for many aquatic species. Thus, species in this area had 375 million years during which to evolve, as opposed to the 10,000 to 15,000 years of more northern areas. The high ridges and low valleys of these mountain ranges have also allowed for the complete isolation of many waterways from one another, thus enabling evolution of species unique to each of these isolated rivers and streams. One ancient species is the hellbender, a huge salamander (reaching a length of over 23 inches, or 60 cm) whose closest relatives live in Japan and China.

Special Features

The Mississippi Piedmont Rivers and Streams ecoregion is a network of waterways originating in mountain ranges that include the Ozark, Ouachita, Appalachian, and Cumberland. Because of the isolation created by the ridges and valleys and the large number of rivers and streams in this region, it is possible to find species that live only in a very limited area or one body of water. The main rivers of the ecoregion are the Tennessee, Cumberland, and Ohio. These and other rivers and streams erode rock and soil as they flow, eventually depositing mineral-rich and nourishing silt in swamps, forests, and farmland.

Freshwater mussels have a parasitic life-stage (glochidia) in which they attach themselves to fish, or sometimes amphibians. These glochidia stay buried in the fish’s tissue for days or months until the capsule they have created explodes and many young mussels emerge to settle on the bottom of the lake or stream. Glochidia attach to gills, fins, lips, barbels, or other portions of the fish’s body. Some mussels need a certain species of fish in order to reproduce, meaning that the mussel has evolved such that only one host fish species will carry its glochidia. Thus, if these fish species become extinct, the mussel species that depends on it for dispersing its larvae will become extinct as well.

Wild Side

The Nashville crayfish is native to these waters, which are shared by fish such as firebelly and duskytail darters, smoky madtoms, palezone shiners, sturgeon, and paddlefish. Salamanders include the West Virginia spring, imitator, shovelnose, and streamside. Any relatively intact stream in this region supports more species of mussels than all of Australia and Europe combined. These species live embedded in the bottom of the stream, river, or lake, where they pump water through their gills and filter out suspended bits of food. Some can be extremely long-lived, including one species that can live for more than 120 years!

Cause for Concern

For decades, the rivers and streams of this ecoregion have been used to transport goods, create electricity, and irrigate agriculture. Such activities have required the building of dams and the digging of canals, which have created problems for native wildlife. The Tennessee River system, for example, has more than 50 major dams, and the impoundments behind them have restricted the movements of many freshwater species. Pollution from cities and farms also threaten aquatic species. Mussels in particular are threatened by sedimentation because they are sedentary and unable to escape from the particles that clog their gills. Introduced species, such as the zebra mussel, compete with native species for resources and habitat.

Looking Ahead

Several conservation and governmental organizations have recently reintroduced lake sturgeon into the French Broad River. This stretch of river is a relatively free-flowing portion of the upper Tennessee River, in which several freshwater mussel and snail species are also making a comeback. Protection and restoration efforts continue on selected streams in high-priority areas (e.g., the Clinch River biopreserve). Continued work, in cooperation with local landowners, is needed to create "buffer strips" of native vegetation along streams and to limit soil erosion.