Maryland Marine Notes: May-June 2001 Sidebar - Managing Exotics in the Chesapeake

Volume 19, Number 3 • May-June 2001

Managing Exotics in the Chesapeake

The Chesapeake 2000 Agreement set as a goal the control and management of invasive aquatic species that could harm the Bay. Signatories to the Bay Agreement are to identify and rank, by 2001, these potential non-native threats to the Bay's ecosystem. By 2003, they are to develop and implement management plans for those species.

According to Edith Thompson, the Exotic/Invasive Species Policy Coordinator for the Maryland Department of Natural Resources, each state in the Bay region – Maryland, Virginia, Pennsylvania and Delaware – is submitting a draft list of those species. The Maryland list currently singles out the following:

Phragmites – Phragmites australis – the common reed, which creates a monoculture of plants, displacing native wetland vegetation. The common reed has little value for native wildlife and can raise the surface level of sediment, changing wetland to upland. Phragmites affects thousands of acres of wetland in Chesapeake Bay, from fresh to brackish marsh.
Mute swan – Cygnus olar – which is beautiful but poses a threat to the Bay's struggling grass beds (SAV). Because the birds are here all year, the exploding Maryland population of mute swans poses a special threat to SAV, potentially affecting its growth during warmer months. The mute swans consume some 9-12 million pounds of SAV each year.
Nutria – Myocastor coypus – an imported rodent that resembles a large muskrat. Nutria eat marsh vegetation, especially three-square bulrush in lower Eastern shore salt marshes, but also fresh and brackish water marsh plants. Nutria have contributed to the loss of over 7,000 acres of salt marsh in the Blackwater National Wildlife Refuge alone.
Green crab – Carcinus maenas – a European transplant that has made its way down the Atlantic coast. Green crabs eat young scallops, which is a special concern in Maryland's Coastal Bays.
Water chestnut – Trapa natans – an invasive plant that can blanket the surface of ponds. Water chestnut creates a monoculture, preventing sunlight from reaching SAV and creating large, spiny seed pods that interfere with recreational use of waterways and beaches.
Purple loosestrife – Lythrum salicaria – a pretty but persistently invasive plant. Like water chestnut, loosestrife creates a monoculture of plants in freshwater wetlands, excluding use of habitat by a diversity of native plants. It appears to have minimal value to native species.

Other top issues facing Maryland include: identifying foreign organisms entering the Chesapeake Bay via ballast water and implementing regulations that require ballast water reporting; controlling exotic/invasive plants in natural areas; mounting a rapid/emergency response to new invasions.

According to the DNR, resident Canada geese (those flocks that do not migrate) are a top priority, currently managed as a game species. Of course, West Nile Virus is also a top state priority, which is managed as a human health issue (by the state Department of Health, with DNR support), and not as an exotic species issue.

DNR also lists five nuisance species that have not yet caused known problems but which may have the potential to be harmful are:

Zebra mussel – Dreissena polymorpha
Grass carp – Ctenopharyngodon idella
Japanese shore crab – Hemigrapsus sanguineus
Rapa whelk – Rapana venosa
Nuclear worm – Namalycastis abiuma
Suminoe oyster – Crassostrea ariakensis

The Maryland DNR has had an Exotic/Invasive Species Policy Coordinator since Feb. 2001. The Coordinator notes that as DNR continues to develop its policy in concert with other agencies and states, the priority listing could evolve and change.

For More Information

Maryland Sea Grant web site on understanding species invasions. Download fact sheets online or order print versions by calling (301) 405-6376. www.mdsg.umd.edu/exotics/ index.html

Chesapeake Bay Program page on exotic species. invasions.si.edu/species.htm

National Invasive Species Council final interagency plan www.invasivespecies.giv/council/ nmp.shtml

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