PORTLAND – A red tide has prompted the state to impose a ban on mussel harvesting along portions of the Maine coast and halt softshell clamming from Phippsburg to Prouts Neck in Scarborough.

“Basically, for clams, Casco Bay is closed, and that probably has shut off approximately 25 to 30 percent of the clam supply in Maine,” said Lori Howell, co-owner of Spinney Creek Shellfish in Eliot.

Red tide are large algae blooms that can accumulate dangerous levels of the neurotoxin that causes paralytic shellfish poisoning. Shellfishing bans linked to red tide can last from several days to weeks.

The current red tide is “pretty average” as far as levels of toxins are concerned, said Amy Fitzpatrick of the Maine Department of Marine Resources.

“It’s more of a typical bloom,” she said. “The trouble is with this weather. It’s just crazy. You get the rainy weather and then the sun comes out for four days. Grass is growing like mad, so we’re worried that the phytoplankton is growing like mad.”

Howell said the clam shortage coupled with increased demand for steamers this time of year is driving up prices.

“They do a great job of monitoring so the public can be assured that what’s out there on the market is perfectly safe to eat,” she said, “but they should understand that they’re probably going to have to pay for that.”

The first shellfish closure of the year occurred in mid-May on the Schoodic Peninsula, when closures occurred for mussels, whelks and snails. Parts of Cobscook Bay were closed as well.

There also are closures for mussels, European oysters and snails from Cape Neddick to Phippsburg and East Boothbay to Friendship. Softshell clam beds are closed from Prouts Neck to Phippsburg, and surf clams are off-limits from the New Hampshire border to Phippsburg.