BOSTON – A corrosive and fast-moving shell disease is making life ugly for lobsters from southern Cape Cod to Rhode Island.

The shell-eating bacteria do not affect the quality of the meat, but leave lobster shells discolored, pitted, cracked and just plain unpleasant-looking. That makes the lobster difficult to sell.

“If you saw this thing sitting in a tank, looking like it was hit by a blowtorch, you’re not going to buy it,” said Bruce Estrella, a biologist at the Massachusetts Department of Marine Fisheries.

Lobstermen are concerned the disease is affecting reproduction and weakening lobsters, making them more vulnerable to predators.

Russ Wallis, 52, a Newport, R.I., lobsterman, said he’s never seen anything like it.

“We don’t have a handle on what it’s done,” he said. “It is scary.”

The disease is caused by the chitinolytic bacterium that eats chitin, a cellulose-like substance in the shells. It’s been seen in lobsters for as long as there have been lobstermen, but now it appears to be spreading more quickly and covering more of the lobster than ever, Estrella said.

“It’s a different strain of bacteria, more virulent and more fast-moving,” he said.

The first lobsters with the accelerated form of shell disease were found near Woods Hole and the Elizabeth Islands in 1997.

It since has been found north to the Cape Cod Canal, south to Martha’s Vineyard and throughout Rhode Island’s inshore waters.

Between 1996 and 1999, the most recent year available, the percentage of lobsters with shell disease in Rhode Island waters rose from 0.09 percent to 12.5 percent among males, and 0.3 percent to 24.4 percent among females.

The lobsters appear to survive the disease fairly well, said Tom Angell, a marine fisheries biologist at Rhode Island’s Department of Environmental Management.

They periodically shed their shells and can completely recover after discarding the diseased exoskeletons, he said.

But affected female lobsters have shed their shells before laying their eggs, killing their offspring before they’re born, Angell said.

It’s unclear if the disease is causing the female lobsters to molt early, he said, but it is a concern.

Scientists can’t yet determine how the disease is affecting commercial revenue. They also don’t know why the disease, which is carried in sediment on the ocean floor, is spreading so quickly, Estrella said.

Some theorize warmer ocean temperatures have allowed the bacteria to flourish. Others blame a 1996 oil spill in Block Island Sound in Rhode Island, or other kinds of pollution.

Even if scientists figure out why the disease is spreading, it’s not likely they can do much to stop it because it’s almost impossible to control a disease in the wild, Estrella said.

“I don’t think there’s anything that can be done to adjust to it except to understand it’s something that’s out of your control and hope it eventually improves,” he said.