PORTLAND (AP) – A partial ban on shellfishing has been imposed along the southern Maine coast in response to red tide concerns.

Soft shell clams have not been included so far, but officials on Tuesday suspended the harvesting of mussels, snails, European oysters and surf clams between the New Hampshire border and Port Clyde.

A localized closure had been issued for the Harpswell area last week.

David Townsend, director of the University of Maine’s School of Marine Sciences, said ocean currents, storm forecasts and other factors raise troubling questions.

“We can see those current-vectors taking that offshore plume of water where these organisms normally grow and blowing them right onto the coastline of western Maine,” Townsend said. “We don’t know that (red tide) cells are growing out there, but we do know the conditions are such that they should be.”

Red tide, or toxic algae bloom, infects shellfish and can make people sick if they eat infected products.

A massive bloom of red tide struck the New England coast last May following stormy weather that blew the phytoplankton from offshore waters to the coast. At its worst, the bloom forced the closure of most shellfish harvesting areas from Maine to Cape Cod.

The outbreak cost shellfishermen heavily in lost income.

Last year’s algae bloom was the worst in New England since 1972. After the 1972 outbreak, New England entered a 10-year stretch of intensified red tides.

Red tide remains an annual threat in Maine and hotspots off Penobscot and Casco bays have been alarmingly active, according to scientists.

A study this year by the Woods Hole Oceanographic Institution in Cape Cod, Mass., showed little threat in southern New England but more cause for concern in Maine.