Lower Mississippi River

About the Area

This ecoregion lies within the lowland Gulf Coastal Plain - a trough between the Appalachians to the east and the Ozark and Ouachita Mountains to the west.

This feature, combined with the Mississippi's high turbidity, has served as a barrier to the dispersal of upland fish species between river systems on either side.

Chosen for representation of large river biota in the Neoarctic, this ecoregion contains numerous examples of fishes, amphibians, reptiles, and invertebrates that have adapted to the unique conditions found in large river systems. Many of these species persist as glacial relicts or are endemic to the river and its tributaries.

Local Species
Among the endemic fishes found in tributaries to the mainstream Mississippi are two minnows (Notropis rafinesquei, N. roseipinnis), one catfish (Noturus hildebrandi), one cavefish (Forbesichthys agassizi), two killifish (Fundulus euryzonus, F. notti), and five darters (Etheostoma chienense, E. pyrrhogaster, E. raneyi, E. rubrum, E. scotti).

The ecoregion is better known for its assemblages of large river fish, which include five lamprey species (e.g., Atractosteus spatula and Lepisosteus spp.), Atlantic sturgeon (Acipenser oxyrhynchus), Lake sturgeon (A. fulvescens), Shovelnose sturgeon (Scaphirhynchus platorynchus), Pallid sturgeon (S. albus), the only North American paddlefish (Polyodon spathula), and bowfin (Amia calva).

Additionally, numerous marine species have been commonly recorded in the Mississippi's lower reaches. This ecoregion also supports a large number of unionid mussel and crayfish species (63 and 57 species, respectively). Aquatic reptiles include American alligator (Alligator mississippiensis) plus two endemic turtles: Ringed map turtle (Graptemys oculifera) and Yellow-blotched map turtle (G. flavimaculata).

Threats
Conversion for agriculture, pollution in the form of sedimentation and pesticide contamination, and wastewater discharges from urban areas - pose major threats to the water quality of these rivers. In addition, extensive hydrological modifications have destroyed the stream habitat for native fishes and other species, such as highly vulnerable native mussels.

Resources

Size:
250,000 sq. km (96,000 sq. miles)

Habitat type:
Large Rivers

Geographic Location:
Southeastern United States: Arkansas, Illinois, Louisiana, Mississippi, Missouri, and Tennessee

Conservation Status:
Critical/Endangered

Quiz Time!

Is true that some existing fish species are treated as fossils?

Answer:
Yes! Paddlefish and sturgeon are considered "living fossils" because fossils of this order date from the Jurassic period -195 million to 135 million years before the present.

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