clear.gif (49 bytes) Zebra mussels in Lake Michigan
A scientist holds up a rock formation with zebra mussels,
which have clogged water-intake systems in Lake Michigan,
U.S.--a modern example of how introduced species can wreak havoc on ecosystems

Charles Bennett-AP/Wide World Photos

Back to Environment: 1960-present

clear.gif (49 bytes)
Comments Credits Recommended Reading On the Web

Copyright (c) 1998 Encyclopaedia Britannica, Inc.