Illinois State Museum


Seeing the Connections

Climate, landforms, and life are all connected. Change in one causes changes in the others, which cause further changes. Studying these connections helps our scientists identify the causes of past environmental change and perhaps even predict the outcome of future changes. Explore with the Changes Institute scientists to see how our environment is full of connections.

river dams map
Map of dams along the Mississippi River

Try this Making Connections Challenge:

Dams, skipjack herring , and ebonyshell mussels - what is the connection?

Ebonyshell mussels once lived throughout the Mississippi River. To reproduce, they produce larvae that can only develop on one species of host fish.

Skipjack herring (click here) are migratory fish that were once common throughout the Mississippi River system. They are host fish for larvae of the ebonyshell mussel.

The Keokuk dam (click here) was the world's largest hydroelectric dam when it was built in 1910. It began operation in 1913. At 10 meters (about 32 ft.) high, it is the tallest dam on the upper Mississippi.

The Connection
The Keokuk dam blocked the river so that skipjack herring could not reach the upper Mississippi River. Without the herring to act as a host for its larvae, the ebonyshell mussel could no longer complete its life cycle. Today, the skipjack herring and the ebonyshell have nearly disappeared from the upper reaches of the Mississippi River.