NARRAGANSETT, R.I. – More lobsters are contracting shell disease, and the problem has spread from southern New England waters all the way to Maine, scientists said Wednesday at a symposium analyzing a phenomenon that has mysteriously afflicted the industry in recent years.

Shell disease now affects 30 percent of lobsters in coastal areas of southern New England and Long Island Sound, according to researchers. It’s still unclear what’s causing the disease, researchers said, and what’s causing it to spread.

“I think it’s important to understand we don’t have the answers yet. We’re starting to get a lot of the puzzle together,” said Kathleen Castro, director of the fisheries extension program of the University of Rhode Island’s Sea Grant program, which hosted the symposium.

The disease does not taint the lobsters’ meat, but makes shells so unsightly that they are too unappetizing to serve whole. It can weaken lobsters so much that they prematurely die, though experts don’t have any concrete figures.

Researchers in the region first noticed shell disease in the 1980s. At that time, affected lobsters’ shells were marked by little black spots. But in the past several years, the researchers said, shells have become fully enveloped by the disease, and in the worst cases had rotted entirely.

On Wednesday, scientists said trawl and trap studies show egg-carrying females are most susceptible to the disease. Those surveys show lobsters living in warmer waters appear to contract the disease more readily.

Hans Laufer, a professor emeritus of molecular and cell biology at the University of Connecticut, said he believes the lobsters may be contracting the disease from alkylphenols, chemicals that are byproducts from industrial sources.

Laufer stressed that his studies were just preliminary.

Another scientist, Roxanna Smolowitz of the marine biological laboratory at Woods Hole, Mass., said bacteria attaches itself to the lobster’s shell and begins to penetrate inward. The lobster tries to fight it off by either molting or generating new, shell-like layers, she said. But the efforts can weaken the organism, making it more vulnerable to predators or another bout with the bacteria.

But panelists agreed that shell disease and possibly other factors, including intensive lobster fishing and predation, have decimated the industry in southern New England and Long Island Sound.

Bob Glenn, a fishery biologist with the Massachusetts Division of Marine Fisheries, said samples taken in 1999 showed lobsters with shell disease were confined mostly to Buzzards Bay. Over the next four years, afflicted lobsters were found for the first time in Cape Cod Bay, Boston Harbor, Outer Cape Cod and as far north as Cape Ann in Maine.

“There’s been a general northward migration of the disease,” Glenn said.

In 1999, the lobster industry in Rhode Island generated $30 million and employed 425 fisherman, according to Mark Gibson, the head of the marine fisheries section in the Division of Fish and Wildlife at the state Department of Environmental Management. Four years later, the industry produced $16.7 million and employed 279.

“Something’s happening before they get to us, and that’s what we need to know,” said Mike Merchant, president of the Rhode Island Lobsterman’s Association.

Panelists said more study is needed to understand what is causing shell disease and how to stop its spread. They will ask state and federal leaders for money to fund further studies.