Invasive plants are displacing Rhode Island’s native vegetation, changing the landscape and making it more difficult for amphibians, fish, and birds to survive.
Conservation groups are fighting back. In Cranston’s Stillhouse Cove, the US Natural Resource Conservation Service has restored tidal flow to eliminate invasive phragmites, a kind of sea plant, and to encourage the return of native marsh grasses. In Providence’s Roger Williams Park, scientists imported a European beetle to stop a purple loosestrife invasion of the zoo’s wetlands. At Middletown’s Sachuest Point, the US Fish & Wildlife Service is struggling to prevent Oriental Bittersweet from overwhelming the refuge.
But once an invader takes hold in ocean waters, warns James Carlton, director of the Marine Studies Program of Williams College and Mystic Seaport, “There’s nothing we can do about it.”
Addressing the annual meeting of the Rhode Island Natural History Survey last month at the University of Rhode Island, Carlton warned of a new threat to Narragansett Bay. Already battered by sewage discharges and other pollution, Rhode Island quahogs and clams will soon face a new six-inch-long shelled predator, the Japanese whelk. First found in Maryland’s Chesapeake Bay in the 1990s, the whelks’ arrival date in Narragansett Bay cannot be predicted, Carlton says, but it is inevitable.
Other maritime species have already colonized local waters. First discovered in Rhode Island in 1993, the Japanese shore crab is now the most common crab in New England, replacing the European shore crab. Codium, a clumpy gelatinous green seaweed also native to Japan, is displacing other forms of seaweed and perhaps eel grass. And in 1997, scientists from URI and Roger Williams University identified the invasion of a five-foot-tall leafy red algae known as Grateloupa turuturu.
The invaders’ impact can be significant, although not always well understood. The Japanese whelk has damaged Maryland’s already shrinking oyster beds. Codium may help transform sandy beaches into rocky shoreline, Carlton says, when it washes ashore, clinging to stones and shells. But New England marine scientists are perhaps most concerned by the growing globs of sea squirts, or Didemnum, in the productive Georges Banks fishery.
By blanketing the ocean bottom, sea squirts may make the ocean floor uninhabitable for sea scallop larvae, according to the US Geological Survey, and prevent fish from feeding on small worms and crustaceans.
Invaders are introduced in many ways, but ballast water used in international shipping may be the most important source. An empty ship leaving Japan to pick up wood chips in British Columbia, California, or Tasmania fills with ballast water, Carlton says. But when it loads its cargo, it empties the ballast water, complete with alien plankton and fish, into another continent’s coastal waters. Because the invasive red leafy seaweed now in Narragansett Bay first appeared in the shipping channel between Newport and Jamestown, it probably originated in ballast water from Europe, theorizes Roger Williams professor Marci Marston.
Some cargo ships now exchange their ballast water in mid-ocean to minimize the problem, Carlton relates, and scientists are also exploring the use of heat, chemicals, or ultraviolet light to sterilize ballast water. In addition, Carlton hopes Congress will enact new ballast water protections when it revises the Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990.
