Non-native species

Non-native or “exotic” species are plants, animals or microbes that have been transported from one geographic region to an area where they did not live previously. The introduction may be intentional as with beef cattle brought to the U.S. from Europe, or unintentional as with Asian mussels carried across oceans in ships’ ballast water. In either case, a non-native species’ full effect on its new environment is often unpredictable.

The Chesapeake Bay watershed has become home to many non-native species — some innocuous, some beneficial, but others destructive beyond our expectations. The non-native honey bee, for example, has developed into a valuable economic and environmental resource. By contrast, the wetland plant, purple loosestrife, has become “invasive” and has completely dismantled its new habitat.

Invasive species

When a non-native species arrives in a new habitat it may find an environment free of natural competitors or controls, allowing it to grow and spread. Termed “invasive,” the unchecked newcomer may outcompete or prey upon native species, and at times alter a delicate ecological balance.

The Chesapeake Bay has been impacted by several invasive species. Two visitors that have found their way to the Bay are pictured at right — the mute swan and the invasive plant, hydrilla.

Although strikingly beautiful, the aggressive mute swan can drive away native birds and devour underwater grasses.

Hydrilla is a poster child for the complexity of the invasive species issue. Some say the plant benefits the Bay by consuming nutrients, producing oxygen, and providing habitat that has helped restore important gamefish in the Potomac River. Others contend that hydrilla displaces native aquatic plants and reduces Bay diversity through the loss of the plants themselves and the animals that depend on them.

Other invasives, like nutria — a beaver-like rodent imported from South America — may damage ecologically valuable marshlands. Still others have proven difficult to detect. Current research strongly suggests, for example, that the deadly oyster parasite, MSX — widely responsible for the demise of the Chesapeake oyster fishery — may have accidentally been brought to the Bay by way of an exotic oyster introduction. Ironically, scientists and managers are now exploring the possibility of introducing a non-native oyster to rebuild the Bay’s oyster reefs.

To help explain the nature and potential impacts of non-native and invasive species in the Chesapeake Bay, the Maryland Sea Grant College has produced a series of videos and fact sheets entitled "Exotics in the Chesapeake." The series is produced in cooperation with the Smithsonian Environmental Research Center, with support from the U.S. EPA's Chesapeake Bay Program and the National Sea Grant College Program, and is based in part on research funded by the Maryland Sea Grant College.