Exotic species are found throughout the Bay’s waterways and landscape — a third of the 3,000 plant species found in Pennsylvania today are nonnative. Here are a few of the region’s more troublesome invaders:

  • Purple Loosestrife: This European wetland plant was probably brought here for ornamental or medicinal purposes in the 1800s. Today, it has overrun more than 1.5 million wetland acres nationwide, crowding out native vegetation, ruining the waterfowl forage base and making wetlands unsuitable for most other wildlife.
  • Chestnut blight: The chestnut blight fungus was accidentally imported from Asia with nursery stock in 1904. It has eliminated mature American chestnuts from the landscape. The chestnut, historically, was a “keystone” species of most eastern deciduous forests, and was one of the most important sources of food for wildlife. It was also a valuable source of lumber.
  • Gypsy moth: Originally imported to Massachusetts in the late 1800s as part of a failed attempt to establish a silk industry, the moth escaped into the wild and has been spreading through New England, Mid-Atlantic and Midwestern states, defoliating and sometimes killing oak forests, which have become more important to wildlife since the demise of the chestnut. Some evidence suggests that defoliated areas “leak” more nitrogen into waterways, and the Bay, than undisturbed forests.
  • MSX: This disease, which appeared in the Bay in the 1950s, is caused by single-cell organism. Since its appearance, the disease has caused losses of up to 90 percent of the oyster population in the Bay. Oysters are important not only for their economic role, but their ecological function. It has been estimated that the Bay’s oyster population could once filter all of the water in the Chesapeake in a matter of days; it takes today’s population about a year to do the same job.
  • Anguillicola crassus: A blood-feeding worm, which historically was found in the Japanese eel, was recently discovered infesting American eels in the Bay and other parts of the East Coast. American eels appear to have less resistance to the parasite, which weakens and reduces the eel’s swimming ability, perhaps affecting its ability to survive the migration to the Sargasso Sea, where it reproduces.