AUGUSTA, Maine — Elevated levels of paralytic shellfish poisoning — also known as PSP or red tide poisoning — have caused much of the Maine coastline to be closed to commercial harvesting for some shellfish. On Tuesday, the Maine Center for Disease Control and Prevention and the Maine Department of Marine Resources reminded Mainers and tourists of recommendations for the safe consumption of shellfish.

Steps people can take to safely enjoy Maine shellfish include:

— Buy from a certified shellfish dealer, whose operations undergo rigorous public health screening and auditing.

— If harvesting shellfish for personal use, make sure the area is not closed because of red tide conditions.

— Do not consume clams or mussels found floating in ocean waters. They are likely to have filtered much more algae-containing water than those from flats or beds, and therefore usually will have much higher concentrations of the toxin that causes paralytic poisoning.

— When eating lobster, do not eat the tomalley, the soft, green substance found in the body cavity of the lobster that functions as the liver. Tomalley serves as a natural filter for contaminants in the water. State and federal advisories against eating tomalley have been in effect for years, mostly because of the presence of PCB toxins, and more recently because of PSP. It is important to note that testing has shown lobster meat is safe to eat.

Paralytic shellfish poisoning is associated with certain types of algae blooms in coastal waters. Bivalve shellfish such as clams, mussels, oysters and quahogs filter water and eat the toxic algae from the water. High concentrations of toxin in these types of shellfish can then cause serious illness or even death if eaten by humans. There is no taste or odor associated with the toxin.

Symptoms of PSP usually include tingling of the tongue, lips and throat that usually begins within a few minutes to two hours of eating contaminated shellfish. This tingling may spread to other areas of the body such as the face, neck and arms. Symptoms also can include headache or nausea, and can progress to weakness, difficulty breathing, and choking. It is important that people with these symptoms seek medical care immediately.

Shellfish that may be unsafe are the following: clams, mussels, oysters, quahogs, snails and whelks.

Fish that are usually safe: crab (meat, not whole crabs); lobster (but not the tomalley); scallops, shrimp and finfish.