PORTLAND – Scientists are blaming the recent stormy weather for a massive bloom of toxic red tide that has forced the closure of shellfish beds along much of the New England coast from Cape Cod to Penobscot Bay.

Red tide is caused by toxic microscopic phytoplankton that normally remain far offshore. But scientists say three blustery storms that have passed through the Gulf of Maine this month, combined with unusual ocean currents, have driven the phytoplankton to the coast.

“It’s wind-driven,” said David Townsend, chairman of the School of Marine Sciences at the University of Maine. “These toxic cells are naturally occurring and isolated from the coast. But they are being pulled towards the coast and raising hell.”

The Maine Department of Marine Resources this week banned the harvest of mussels and European oysters from the New Hampshire border to Brooklin. It also banned clam-digging from the New Hampshire border to Phippsburg.

New Hampshire officials banned shellfish harvesting until further notice, and Massachusetts officials have banned shellfish harvesting from Cape Cod to the New Hampshire border.

The closures are bad news for Maine’s roughly 2,000 licensed clam diggers. Chad Coffin of Freeport said the arrival of a huge bloom so early in the season indicates that clam flats are going to be closed for a long time.

Two years ago, clam flats were closed for nearly two months in the Down East communities around Cobscook Bay. A widespread closure of that scale would be devastating for diggers who depend on clams for their livelihood, Coffin said.

“There are families where everything is provided by clams,” he said. “There is definitely going to be severe economic hardship born of this red tide.”

Neal Pettigrew, an oceanographer at UMaine, said an unusually strong ocean current also is pushing the red tide from the eastern Gulf of Maine to the gulf’s western shores.

He said satellite photos show a blue ribbon of cold water traveling from Penobscot Bay to the New Hampshire shore. The cold current, which is normally much weaker this time of year, continues south into Massachusetts waters, he said.

Red tide doesn’t harm mussels or clams, which flush out the toxin after it disappears from the waters around them. But for humans, the toxin in red tide is among the most potent found in nature. At high levels, it can cause numbness, tingling, dizziness, nausea and even death.

Lobsters, crabs and shrimp do not accumulate the toxin and are safe to eat.