Toxic red tide algae continue to affect shellfish beds in parts of Down East Maine even as the problem appears to be abating somewhat in southern areas of the state.

The Maine Department of Marine Resources has extended the ban on collection of mussels, European oysters and carnivorous snails from the southwestern tip of Moose Neck near Addison to the Canadian border.

Harvesting of soft-shell clams is banned from Cutler north but still permitted in specific areas of Cobscook Bay, but the entire bay is closed to all other shellfish collection. For more information, go to DMR’s Web site, http://www.maine.gov/dmr.

Conditions are improving along the southern coast, meanwhile. And because of an extensive monitoring program, all Maine shellfish that are sold commercially in the state come from areas unaffected by red tide.

DMR lifted the ban on soft-shell clam harvesting from the Maine-New Hampshire border to Cape Elizabeth. The ban remains in effect for mussels, oysters, snails and surf, or hen, clams. The DMR once again is allowing collection of mussels in most of Casco Bay, according to information provided by Darcie Couture, director of DMR’s biotoxin monitoring program.

Red tide is caused by blooms of naturally occurring algae that produce a toxin that then is absorbed by shellfish as they feed. Eating shellfish affected by the toxins can cause sickness or death in humans.

Experts had predicted that the 2008 season could be a bad one for red tide based on the number of algae seeds, or cysts, found offshore. Because of differing tidal currents, Down East Maine can experience large red tide blooms while southern or western regions do not, and vice versa.

During the last large outbreak 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, an assistant professor of natural resource economics at the University of Maine at Machias.

Despite the closures, Maine harvesters still sold more than 7 million pounds of clean shellfish in 2005 because of the state’s monitoring program.