The worst bloom of toxic red tide in the history of New England closed in on the Vineyard yesterday after shellfish beds were shut down from Maine to Nantucket, and anxious Island shellfishermen awaited word about a possible closure in their own waters.

"I am just hoping it doesn't come here," said Rob Garrison, director of the solar hatchery run by the Wampanoag Tribe of Gay Head (Aquinnah).

"It certainly is close," said Rick Karney, director of the Martha's Vineyard Shellfish Group.

Intensive sampling began on the Vineyard over the weekend and went on through the day yesterday. Shellfish samples were collected from Oak Bluffs and Edgartown and sent to state laboratories for testing. Word went out around the waterfront that state biologists would know the results by 3 p.m., but as the afternoon wore on there was still no word of any official closure.

Oak Bluffs shellfish constable David Grunden collected water samples in Nantucket Sound, a mile out from the Big Bridge, using a plankton net, and after analysis concluded that he had found Alexandrium fundyense, or red tide.

"I told Mike Syslo [director of the state lobster hatchery on the Vineyard] about it and my guess is I wouldn't be surprised if we aren't closed right away or in the very near future," said Mr. Grunden.

At press time the closure had been extended from Nantucket to the shoreline of East Beach on Chappaquiddick to south of Norton Point Beach.

A closure would force nearly a hundred commercial shellfishermen on the Vineyard out of work. Last night Steven Wong of Aqua World Seafood Corp. in Vineyard Haven said he had been instructed not to buy conch from Vineyard fishermen.

A highway of red tide cells has been pushed south by a freshwater current, to the surprise of state biologists. On Friday J. Michael Hickey, the senior state shellfish biologist for the Division of Marine Fisheries, said he did not think the tide would make it to the Vineyard. One day later Nantucket was closed, and yesterday Mr. Hickey revised his forecast.

Caused naturally by an explosion of single-celled organisms that collect in clams, mussels and other shellfish, red tide can cause illness and even death if ingested by humans. The species of algae is unlike the variety that occurs off the coast of Florida and does not emit fumes, kill fish or prevent people from swimming. It only affects bivalves and not other sea creatures like lobster and shrimp.

Scientists believe the bloom was caused by an unusually cold and wet winter and spring.

Shellfish beds are now closed from central Maine to Chatham, including all of Cape Cod Bay, parts of Bourne and Wareham in Buzzards Bay, Pleasant Bay and the eastern end of Nantucket Sound. On Cape Cod the closures have brought a multimillion-dollar summer shellfish industry to its knees.

Meanwhile, yesterday a dozen conch fishermen leaving from Edgartown and Oak Bluffs learned that they were shut out of the waters of Nantucket Sound.

The bloom was first discovered in the Gulf of Maine by scientists aboard the 177-foot research vessel Oceanus from the Woods Hole Oceanographic Institution. A familiar species in Maine, the cold water algae is usually found in extremely low amounts. Scientists believe that rainwater entering the ocean and predominant winds from the east-northeast helped to create a biological perfect storm that encouraged the algae to bloom at an explosive rate.

"All the conditions were right for a major outbreak of Alexandrium fundyense, the predominant red tide species in the Gulf of Maine," wrote Don Anderson, a biologist and senior scientist for the Woods Hole Oceanographic Institution, in a news release this week. " We've had patches of red tide cells at the entrance to Massachusetts Bay just south of Cape Ann on other occasions, but often the winds and circulation patterns take them offshore. This time, we had high cell concentrations to the north, evidenced by very high levels of toxicity along the New Hampshire coast and then the unusual winds and currents brought them into the bay, where we found them in a broad distribution from Cape Ann to Stellwagen Bank."

On Sunday morning Mr. Syslo joined down-Island shellfish constables to collect shellfish samples to be sent to Gloucester for testing. The results came back clean.

But yesterday afternoon shellfish constables were asked to go back out again and collect more samples for additional testing.

Mr. Grunden and Mr. Syslo collected mussel samples from the rocky shoreline of East Chop and from the Oak Bluffs Steamship Authority wharf. Shellfish were also collected in Sengekontacket Pond. Edgartown shellfish constable Paul Bagnall said softshell clam samples collected in Edgartown Great Pond and quahaugs at Eel Pond were found to be clean.

The Vineyard shellfish industry is healthy and growing, aided by burgeoning oyster farming activity in Katama Bay and at the tribal hatchery in Aquinnah.

Mr. Garrison said the tribe is set to sell 15,000 to 20,000 of its signature Tomahawk oysters per week. "We plan on shipping out on Wednesday morning [tomorrow]. Our oysters go to Boston, New York and Washington, D.C.," he said.

"I am just hoping there is not a statewide closure," said Louis Larsen, who owns the Net Result fish market in Vineyard Haven. Mr. Larsen only sells locally harvested shellfish, which he buys from a crew of loyal shellfishermen.

Mr. Bagnall expressed surprise at the rapidly unfolding events. "To my knowledge it has never shown up here," he said. "We got the northern red tide in the Gulf of Maine and we got the southern red tide that sometimes gets into the Chesapeake and the Delaware. Forever we have been in the middle of the two species."