News and ResourcesMaryland Invaders - February 19, 2017
Throughout Maryland there is a growing problem with non-native invasive species. As global trade and transportation have become major facets in our everyday lives, the susceptibility of coastal areas, such as Maryland, to fall victim to harm from invasive species has increased significantly.
The Maryland Department of Natural Resources defines an invasive species as showing tremendous capacity for reproduction and distribution throughout its new home and having a negative impact on environmental, economic, or public welfare priorities. Invasive species can range from microscopic plankton to mammals, to reptiles and even fish. However, regardless of the species’ size, they all can pose a serious threat to local ecosystems.
Invasive species are problematic because they can aggressively establish themselves after introduction, and often end up in direct competition with native species. Because of this, invasive species can quickly and dramatically alter natural habitats and displace native flora and fauna species. In the U.S. alone, 45 percent of species that are listed as rare, threatened, or endangered are designated in this category in part due to invasive species.
In Maryland, we have a number of invasive species that include both plants and animals. Many have traveled here from surrounding states, and others have been introduced, both accidentally and on purpose. Some, such as the zebra mussel, are hitch-hikers in the ballast waters of ocean-going vessels. Others were intentionally introduced, such as the European starling, in an effort to introduce every bird mentioned in Shakespeare’s work to the United States.
One species that was introduced to the United States for its appearance and grace is the mute swan. Mute swans are native to Europe and Asia, but were introduced to North America in the late 1800s to add elegance to public parks and estate ponds. The Maryland population originated when five captive birds escaped from an estate in Talbot County in 1962. The population increased dramatically from 264 birds in 1986 to nearly 4,000 in 1999. After a population control effort initiated by the Maryland Department of Natural Resources in 2005, the population was reduced to less than 100 birds by 2012.
Mute swans are one of the most aggressive species of waterfowl in the world, especially during breeding season. They displace colonial waterbirds, such as the state endangered royal tern, from their nesting and feeding habitats. Mute swans feed on submerged aquatic vegetation (SAV), ripping out the whole plant, including the roots. A single swan can eat more than 8 pounds of SAV a day. This reduces the amount of SAV available for other species of native waterfowl, while damaging important SAV habitat.
Another invasive species that was introduced for its aesthetic appeal is non-native wisteria. There are two species of invasive wisteria found in North America, Japanese and Chinese. Chinese wisteria was introduced to the United States in 1816 for horticultural purposes. Shortly afterwards, Japanese wisteria was brought over in 1830. Producing beautiful, showy flowers with a pleasant scent, these plants quickly became a popular addition to gardens across the country.
Wisteria vines grow around nearby vertical structures, which often end up being trees. Over time, the vines will tighten and strangle branches, sometimes killing the tree. The vines can eventually encompass the tree, blocking vital sunlight, which can also cause the tree to die. When trees die off and leave an opening on the forest floor, wisteria can grow into dense thickets. An individual wisteria plant can live up to 50 years and grow to heights of 70 feet. They can reproduce by both seeds and through vegetative growth of existing runners.
Two invasive crab species are of emerging concern in Maryland. The European green crab and Japanese shore crab have been documented in parts of the Coastal Bays. Currently, the green crab has only been found in Isle of Wight Bay, while the Japanese shore crab has been documented in Isle of Wight, Sinepuxent, and Chincoteague Bays. Both species increase competition among native species for food and habitat. Green crabs may also have a negative impact on shellfish and SAV populations, but the specific effects of this species are still unknown. The green crab is frequently used as live or frozen bait for fishing. It is important for fishermen not to release live bait into the water, and to properly dispose of the invasive crabs.
To help combat the spread of invasive species, there a few simple actions you can take. The easiest and cheapest way of fighting invasive species is to prevent their introduction in the first place. Before purchasing a new plant, check to see if it is a known invasive plant and try to plant native plants to create a better habitat. Before traveling, clean your shoes, clothes, and other belongings to make sure you have no hitch-hikers on board. When boating, make sure your gear and boat are clean before boating in a new location or body of water. By taking these simple steps, you can help prevent the spread of invasive species in Maryland.
Phillips is the Program Manager for the Maryland Coastal Bays Program. Jackson is the former Education Coordinator for the Maryland Coastal Bays Program and current graduate student at Clemson University.
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