Just as this summer’s record-breaking red tide bloom seemed to be subsiding, a fresh batch of the toxic plankton has materialized near the Canadian border.

Within the next week, red tides – particularly in the northern parts of the state that were spared the worst of the June bloom – could reach dangerous levels, according to the Maine Department of Marine Resources.

“It’s just starting to head in a bad way,” said Darcie Couture, director of biotoxin monitoring for the DMR, said Tuesday.

“There’s a pretty significant bloom out there,” she said. “It looks like this will be the big hit for Down East Maine.”

Already, the closures are being enlarged, with the northern boundary of one area shifted a few miles east from Youngs Point in Corea to Petit Manan Point in Steuben. Farther south, harvesting again was banned in an area that had been reopened near Port Clyde, Couture said.

Toxin levels in some of the shellfish samples from closed areas in Penobscot Bay have increased eightfold in the past week, she said.

The plankton that causes red tide, Alexandrium tamarense, is found naturally throughout the Gulf of Maine. But when ideal conditions send it into reproductive overdrive, the resulting blooms – which take on a red tinge in extreme cases – are dangerous.

The plankton produce toxins that can be deadly when birds, wildlife or people eat contaminated shellfish. Filter feeders such as clams, mussels and oysters can take in so much toxin that eating them produces effects ranging from severe food poisoning to, in rare cases, death. No one in Maine has died of the condition, called paralytic shellfish poisoning or PSP, since the state started monitoring plankton blooms 50 years ago.

Alexandrium thrives in the cold, oxygen-rich waters of a current that passes through the Gulf of Maine several miles offshore. Late every summer, the sunshine sparks at least a small bloom as plankton drift toward the coast. The population that scientists now are detecting offshore, however, has appeared about two weeks ahead of schedule, so exactly what’s happening isn’t clear, Couture said.

The worst-case scenario in the next few days would involve a storm moving from the northeast, with winds that could carry this newest bloom to shore, Couture said. That’s precisely how the plankton that sparked the unusual westerly bloom earlier this summer made their way to clam flats, according to scientists researching the phenomenon.

For the next few days at least, meteorologists at the National Weather Service office in Caribou are predicting thunderstorms in conjunction with a cold front moving northwest to southeast – away from the coast.

That doesn’t ease the concerns of DMR scientists. Couture said Tuesday that she fully expects to see a new bloom soon, beginning Down East and likely expanding south and west along Penobscot Bay as it grows. The predictions for southwestern Maine, where the current that carries Alexandrium runs farther out to sea, are rosier, Couture said.

And in Massachusetts large regions of the coast are being reopened to fishing. Including new openings to be announced today, half of the areas that were closed at the peak of the bloom are now open, said Dave Whittaker of the Massachusetts Division of Marine Fisheries office in Pocasset.

“We’re slowly, surgically opening,” he said.

At its worst in late June, the red tide bloom had affected a majority of the New England coastline, shutting down shellfishing beds and prompting Gov. John Baldacci and his Massachusetts counterpart to declare a state of economic emergency.

The federal Small Business Administration approved Maine’s request for economic relief and offered “disaster” loans at 4 percent interest to fishermen and shellfish dealers, according to Lew Flagg, deputy commissioner of Marine Resources. More than 120 people from the fishing industry attended a series of meetings about the disaster relief held across the state in recent weeks, he said.

As of Tuesday, 23 Mainers had applied for the loans and two of those loans had been approved for a total of $6,200, said Colleen Hiam, a spokeswoman for the SBA’s disaster office in Niagara Falls, N.Y.

For updates on red tide closures, visit the Maine Department of Marine Resources Web site at http:// www.state.me.us/dmr/rm/publichealth/closures/pspclosures.htm