APPLEDORE ISLAND, N.H. – The discovery of Asian shore crabs off New Hampshire is further proof the species is spreading rapidly in the region, threatening extinction of native species, scientists say.

The Asian shore crab, or Asian red crab, is native to the western North Pacific. It was found last week on Appledore Island by the 8-year-old son of James Moran, director of the Shoals Marine Laboratory on the island.

A second red crab was found a day later.

Moran said the Asian crab now is the most common crab in Long Island Sound, displacing another invasive species, the green crab, which also is along the New Hampshire coast.

Neither the red nor green crab has commercial value, but they could cause extinction of other native and long-term species in the area.

“The Asian red crab will take over presumably the entire intertidal area,” Moran said. “In the New York area, under any rock you turn over there are four to five of them.

“Probably the same thing will happen here and probably the green crab will become very rare,” he said. “We don’t know what other consequences will happen from there.”

The Asian shore crab was first found in the United States in 1988 in the New York-New Jersey area. Moran said it continues to spread and was discovered in Cape Cod Bay four years ago.

Last year, it was found near Odiorne Point State Park in Rye, and a week ago, it was found in Wells, Maine. Biologists have charted its presence along the Atlantic coast from North Carolina to Maine.

The Asian shore crab is believed to have come to America from Japan in the ballast water of freighters.

Moran said marine biologists do not think the red crabs will spread into the area’s wetlands. There was similar concern with the green crab, but it did not enter wetland areas. The primary concern would be what damage the invaders would have on commercial soft-shell crabs.