Invasive Species

Invasive & non-native organisms can threaten native species

Recommendations

• Develop and implement a monitoring plan for invasive and non-native species.

• Research the impacts of non-native crabs on native crab species.

• Educate anglers to not release live crabs, as this assists their spread.

Nuisance waterfowl species threaten the bays

Since early colonization of North America, new species have been introduced at a never-increasing rate. These species have arrived through a variety of pathways, including through the ballast of ships (e.g., zebra mussel), in the wooden packing material of imported goods (e.g., Asian long-horned beetle), and through deliberate import for various uses (e.g., green crab). While most of these introduced species are benign, about 15% become invasive.

An invasive species shows a tremendous capacity for reproduction and distribution throughout its new home, and also has a negative impact on environmental, economic, or public welfare priorities. Many introduced species do not show a propensity to become invasive for several generations, so species that were once thought to be beneficial, such as grass carp, European starlings, mute swans, and nutria, have demonstrated the characteristics of invasiveness long after their original introduction. These and other species are proving difficult to control in their competition against native species for food, shelter, water, or other resources, and their impacts on economic interests and human welfare. Without the disease and predators that they contend with in their native habitats, the spread of these species can be rapid and the efforts to control them can reach billions of dollars.

When ecologists talk about the impact of introduced species on native species and habitats, they mean that the introduced species is reproducing and distributing itself so efficiently that it is out-competing native species’ use of the same habitats. Even native species can become nuisance species when their populations increase due to human induced changed to their environment, e.g., increased availability of food. Nature is a very delicate balance, much altered by humans, and the protection of remaining natural interactions between native species and their habitats are the responsibility of local, state, and federal agencies, as well as all citizens.

Two species of nuisance waterfowl— mute swan (Cygnus olor) and resident Canada goose (Branta canadensis)—are widely distributed in Maryland waters. Throughout Maryland, mute swans peaked in 2003 at approximately 3,600 birds and resident Canada geese numbered around 75,000 birds in 2004.6,8 Mute swans eat seagrasses, which compromises this valuable habitat and reduces the amount of food available for native migratory waterfowl. They also aggressively defend their nests, often displacing native waterfowl from their breeding areas. The normally migratory Canada goose has established large year-round resident populations in the Coastal Bays and neighboring Chesapeake Bay. Like the mute swan, these resident Canada geese impact food and habitat for native migratory species. Conflicts between humans and these two invasive species include: damage to agriculture, parks, golf courses, and residential properties; bird strikes with airplanes and automobiles; and potential disease transmission.

• Continue public outreach to recognize mute swan, resident Canada goose, and snow goose population impacts to the environment and humans.

• Continue resident Canada goose population management (egg addling, removal of adults, habitat modification, resident Canada goose hunting) to protect property and agricultural crops, minimize human safety issues, and reduce health concerns.

• Manage mute swan, resident Canada goose, and snow goose populations at sustainable and appropriate levels for environmental and sociological conditions to minimize impact to native wildlife and habitat.

• Continue to monitor the population and distribution of mute swan, resident Canada goose, and snow goose populations and evaluate the effectiveness of management actions.

There are non-native crayfish in the Coastal Bays.

The red swamp crayfish (Procambarus clarkii) is a non-native crayfish that has been introduced into freshwater streams in the Coastal Bays watershed. This species is large and aggressive and is likely to affect populations of native crayfishes, freshwater mussels, and amphibian species through direct competition and predation. Currently, feral populations of this species are known from Scarboro Creek and Pawpaw Creek, tributaries of Chincoteague Bay.

Invasive plants are reducing species diversity

Invasive plants are plants that can thrive and spread beyond the areas of the world in which they evolved. They reproduce quickly and prolifically and are often adapted to disturbance. They are typically introduced by people, either accidentally or intentionally. Invasive plants can reduce species diversity, because they can crowd out, shade out, and grow over less aggressive plants in the habitats they invade. They disrupt food webs because they do not provide the same feeding and nesting opportunities as plants that co-evolved with the animals in a given ecosystem.

Invasive species can also change water and nutrient flows, soil pH, fire susceptibility, and light availability.

Although many troublesome invasive plants were originally imported for ornamental or medicinal purposes, two species that are especially problematic in the Coastal Bays were accidental introductions—the common reed and Japanese stilt grass (Microstegium vimineum). Another Coastal Bays invader, Japanese knotweed (Polygonum cuspidatum), was an ornamental introduction. The common reed (often colloquially referred to as “Phrag”) has actually existed on the East Coast of the United States for over 4,000 years. In its historic Maryland form, it occurred in mixed stands with other tidal wetland plants. During the mid- 19th century, commercial sailing ships accidentally brought a European strain of the plant, genetically different from those already here, to U.S. shores in their ballast water. The European reed was much more aggressive than the American variety, and by the 1940s had virtually replaced the historically occurring grass.

The common reed can form large monocultures along the Coastal Bays shorelines, taking over space normally occupied by other plants. Most marsh inhabitants cannot use it for food or shelter. The tall stalks blow over during the winter, forming a heavy layer among their own roots, changing the marsh surface height and hydrology. It should be noted that the common reed does provide some benefits, such as shoreline stabilization and water quality maintenance.

Japanese stilt grass, or Nepalese browntop, is an Asian annual grass that spreads rapidly along disturbance corridors like trails and creek edges. It can thrive in low light, and spreads by rooting at the nodes and dispersing seeds. Japanese stilt grass changes forest floor diversity by shading out perennials.

White-tailed deer—major herbivores in forested systems—do not appear to eat Japanese stilt grass, leaving it untouched in preference for native species. Japanese knotweed was introduced into the U.S. from Asia in the late 1800s, for use as a garden plant and for erosion control. This plant spreads primarily by long, jointed rhizomes, which can grow for meters just under the soil surface, and which sprout to form huge colonies. Almost any broken fragment of the plant can root and become a new individual. Knotweed infestations shade out plants that live below their canopy. Every effort should be made to limit the spread of invasive plants in order to protect the watershed’s native biological communities.

Potential Forest Invaders

Exotic and native diseases and insects, such as gypsy moths and pine beetles, are always present and periodically damage trees. Most outbreaks generally have not caused long-term changes in forests in the Coastal Bays areas, which could change with some new exotic pests already found elsewhere in the U.S.

Invasive exotic species that have reasonable potential to be introduced in the near future include:

• Emerald ash borer: A beetle that kills native ash species, currently spreading in the Midwest and Canada, with pockets found in Maryland and Pennsylvania.

• Asian long-horned beetle: A beetle that can kill maples, poplar, willows, and others and has been found in solid wood packaging in ports on the East Coast.

• Sudden oak death: A disease that can kill or damage many oaks, rhododendrons, viburnums, camellias, and others. It is found in California and Oregon and is being shipped in nursery stock nation-wide despite control efforts.