The red tide appears to be turning.

For the first time in weeks, all of the Maine coast again is open to harvesting clams due to steady declines in levels of the toxic algae known as red tide.

Collection of mussels, oysters and some other shellfish is still restricted in certain areas. But a marine biologist said Friday that she hopes to begin lifting those prohibitions within the next week or two as red tide along the coast of Maine finally begins to come down from record-high levels.

“Everything is moving in the right direction,” said Darcie Couture, director of the state Department of Marine Resources’ biotoxin monitoring program.

That should come as welcome news to shellfish harvesters and dealers who have been dealing with extensive closures for more than two months.

Red tide is caused by blooms of naturally occurring algae that produce a toxin that is absorbed by shellfish as they feed. The algae does not sicken the shellfish, but eating clams, mussels and other shellfish with high levels of toxins can cause sickness or death in humans.

Red tide is always present off the Atlantic coast. But levels of the algae vary dramatically from year to year in the coastal waters that support Maine’ s sizable shellfish industry. And 2008 has been arguably the worst year on record.

DMR operates an aggressive monitoring program that tests shellfish and closes areas as red tide before “scores” reach potentially dangerous levels. That monitoring program ensures any shellfish sold by certified dealers have been collected in areas deemed safe by DMR.

The department was forced to prohibit clam harvesting in areas that had never before been closed, particularly in Hancock and Washington counties.

Red tide contamination became so high that, for the first time, the state detected potentially toxic levels in the tomalley, or liver, of lobsters. That prompted Maine health officials and later the federal Food and Drug Administration to reiterate their long-standing warnings against eating lobster tomalley. Toxins do not accumulate in lobster tail or claw meat, however.

Couture said Friday that the red tide scores have leveled off in recent weeks and clams have been purging themselves of the toxins, thereby allowing the department to reopen clam flats in the southern, Down East and Acadia regions of Maine.

Harvesting of mussels, European oysters and carnivorous snails is still prohibited for large areas stretching from south of Mount Desert Island northward to the Canadian border, including Cobscook Bay. Some areas of southern Maine remain closed as well.

But Couture said she hopes those areas will clear up in the coming weeks.

“It takes them a little bit longer,” Couture said of mussels. “Even though they are very efficient pumpers, they get up to much higher levels [of toxicity] than clams do.”

Mahogany clam beds remain closed as well.

While the closures undoubtedly affected Maine’ s shellfish industry — and particularly local harvesters in restricted areas — the effects were lessened by DMR’ s monitoring program. Using federal grants from the previous major red tide event in 2005, DMR installed monitoring buoys and hired additional staff, which allowed the department to be very precise as to which areas needed to be closed.

Jim Markos, general manager of Maine Shellfish Co. in Ellsworth and Kennebunk, said that made a substantial difference.

“Compared to 2005 & life has been a lot better,” Markos said. “The monitoring system DMR developed allows for more areas to remain open because it allowed them to do a more surgical evaluation.”

In 2005, harvesters suffered about $4.8 million in economic losses because of shellfish bed closures. The total economic impact for the state in 2005 was about $12 million, according to research by Kevin Athearn, assistant professor of natural resource economics at the University of Maine at Machias.

DMR will continue to monitor shellfish beds for red tide into October in case the state experiences a rare, autumn bloom.