Harmful Algal Blooms Facts

Alexandrium Species—Paralytic Shellfish Poisoning (PSP)

For more on PSP, see our detailed information on Paralytic Shellfish Poisoning in Alaska.

Pseudo-nitzschia Species—Amnesic Shellfish Poisoning (ASP)

Several species of diatoms (phytoplankton algae) in the genus Pseudo-nitzschia produce the neurotoxin domoic acid, which causes a condition called amnesic shellfish poisoning (ASP) in humans. When shellfish and plankton-eating fish such as herring, capelin, and sand lance consume the diatoms, domoic acid can accumulate to very high levels without negatively affecting the fish. The toxins can be passed up the food chain to fish, birds, marine mammals, and humans that consume the shellfish and fish, causing illness and sometimes death.

Domoic acid has been responsible for the deaths of hundreds of California sea lions, and the cause of reproductive failure in many others. It appears almost yearly along the California coast.

Domoic acid poisonings in history have been rare or undocumented. No cases of ASP in humans have been reported in Alaska, but domoic acid has been responsible for illness in more than 100 people in North America and several deaths. Domoic acid–producing species are present in Alaska, however, and environmental changes that support algal blooms could increase their abundance and range in Alaska.

ASP human symptoms

In humans, the toxin causes gastrointestinal and neurological symptoms. Typically within 24 hours gastrointestinal symptoms appear, including:

In more severe cases neurological symptoms can occur within 48 hours, including:

ASP treatment

There is no antidote for ASP and treatment is supportive only. The potency of ASP toxins appears to be less than for PSP, but if ASP toxins are ingested in high enough concentrations they can be very dangerous and have been known to cause death in several people. Seek medical attention if you exhibit any symptoms of ASP after consuming shellfish.

Report any cases of suspected and confirmed amnesic shellfish poisoning!

If one case occurs, there will likely be others and reporting even mild cases may save another person’s life. Health care providers and citizens should report any suspected case of ASP immediately to the Alaska Section of Epidemiology. To report, call 907-269-8000 (Mon–Fri 8 am–5 pm) or 1-800-478-0084 (after hours).

Types of seafood that pose a risk for ASP

Any organism that consumes the algae species that contain domoic acid, and organisms that consume those organisms, can pose a risk to humans. All recreation and subsistence harvested bivalve shellfish, including mussels, clams, geoducks, oysters, and scallops, can contain domoic acid. Crab meat is not known to contain domoic acid, but their guts can contain the toxin from feeding on contaminated shellfish. Before cooking, remove the back shell of the crab and take out the dark soft tissue that makes up the digestive system and crab butter (hepatopancreas).

Marine mammals in Alaska have been shown to contain low levels of domoic acid. In other regions of the United States, such as California, domoic acid poisoning has killed many marine mammals. It is unknown whether marine mammals can acquire high enough levels of domoic acid in their tissues to pose a risk to humans who consume them. To date, no case of ASP has been reported in Alaska from consuming marine mammals. As domoic acid becomes more prevalent it is important to remain aware of the risk and know the symptoms of ASP.

Consuming recreationally collected shellfish in Alaska

Both domoic acid and PSP toxins can accumulate in shellfish in Alaska, and recreational beaches are not tested for these toxins. Cooking or freezing shellfish does not destroy the toxins. It is best not to consume recreational and subsistence collected shellfish. Commercially bought bivalves (clams, mussels, and scallops) are tested for toxins, and are safe to consume. Crabs can also accumulate toxins in their digestive systems, but they are not regularly tested for algal toxins. It is recommended that you clean your crabs, removing the guts and crab butter, before cooking.

For more information on domoic acid and amnesic shellfish poisoning

Dinophysis Species—Diarrhetic Shellfish Poisoning (DSP)

Dinophysis is a dinoflagellate alga that produces multiple neurotoxins including dinophysistoxins and okadaic acid. Shellfish consume the toxic algae and can retain the toxins in their tissues. When humans consume shellfish that have accumulated toxins, they can become ill. In humans, the illness is called diarrhetic shellfish poisoning (DSP). DSP has not been documented in Alaska, but it is an emerging health threat in Washington and has been documented in Canada. In summer 2011, the first confirmed DSP illnesses were documented in Washington in three people who had consumed recreationally harvested mussels. DSP may become a threat for Alaska in the future.

DSP human symptoms

DSP causes gastrointestinal symptoms in humans. Symptoms typically occur from 30 minutes to a few hours after the consumption of contaminated shellfish. Symptoms can include:

There have been no deaths reported from DSP. A full recovery typically occurs within 3 days of exposure, with or without medical treatment.

DSP treatment

For mild symptoms, call your health care provider. If symptoms are severe call 911 or have someone take you to the hospital immediately. Treatment usually involves replacing fluids and electrolytes lost during the illness. Generally, hospitalization is not needed and fluids can be replaced orally.

Report any cases of suspected and confirmed diarrhetic shellfish poisoning!

DSP has not been reported in Alaska to date, but it may occur in the future. If one case occurs, there will likely be others and reporting even mild cases can be very helpful in preventing illness in others. Health care providers and citizens should report any suspected case of DSP immediately to the Alaska Section of Epidemiology. To report, call 907-269-8000 (Mon–Fri 8 am–5 pm) or 1-800-478-0084 (after hours).

Types of seafood that pose a risk for DSP

Any organism that consumes the algae species that contain DSP toxins, and organisms that consume those organisms, can pose a risk to humans. DSP is usually reported from consuming contaminated bivalve shellfish, including clams, mussels, oysters, geoducks, and scallops.

Consuming recreationally collected shellfish in Alaska

Many types of algal toxins can accumulate in shellfish in Alaska, including domoic acid (amnesic shellfish poisoning), paralytic shellfish poisoning toxins, and possibly DSP toxins. Recreational beaches are not tested for these toxins. Cooking or freezing shellfish does not destroy the toxins. It is best not to consume recreational and subsistence collected shellfish. Commercially bought bivalves (clams, mussels, and scallops) are tested for toxins, and are safe to consume. Crabs can also accumulate toxins in their digestive systems, but are not regularly tested for algal toxins. It is recommended that you clean your crabs, removing the guts and crab butter (hepatopancreas), before cooking.

For more information on diarrhetic shellfish poisoning

Cyanobacteria

Cyanobacteria, commonly called blue-green algae, are found in fresh, brackish, and marine waters. Cyanobacteria blooms typically form in warm, slow-moving waters that are high in nutrients such as nitrogen and phosphorus. The bloom can appear as foam, scum, or mats on the surface that are several inches thick. The color of the bloom can vary from no color change to blue, bright green, brown, and red.

Some species of cyanobacteria produce cyanotoxins, which are harmful to both wildlife and humans. It is not possible to determine if a bloom is toxic by just looking at it. Cyanotoxins can cause skin irritations, damage to the liver, gastrointestinal symptoms, neurological symptoms, and even death, depending on the species of cyanobacteria. The blooms of greatest concern occur in fresh waters, such as drinking water reservoirs or recreational waters.

Cyanobacteria blooms can pose a risk to humans through exposure to contaminated freshwater via recreational activities on the water, and the consumption of contaminated drinking water, fish, and shellfish. Large blooms may also deplete the oxygen levels in water and can cause death among local populations of plants and animals.

For more information on cyanobacteria