Caretakers versus Exploiters: Impacting Biodiversity in the Age of Humans

Seafood Borne Illnesses

The Food and Drug Administration identifies five types of toxic algae that are known to impact humans. The types include Paralytic Shellfish Poisoning (PSP), Amnesic Shellfish Poisoning (ASP), Diarrhetic Shellfish Poisoning (NSP), Diarrhetic Shellfish Poisoning (DSP), and Azaspiracid Shellfish Poisoning (AZP). Ciguatera Fish Poisoning (CFP) is also a concern to humans. Each type of seafood poisoning is categorized by the genus type of algae that produces a specific type of toxin resulting in the type of seafood poisoning. This curriculum unit will look at PSP and ASP as they are the most common types of seafood poisoning that occur from consuming seafood sourced from California coastal waters.

Amnesic Shellfish Poisoning (ASP)

Amnesic Shellfish Poisoning (ASP) is caused by the ingestion of seafood that has the neurotoxin domoic acid produced by the algae Pseudo-nitzschia australis. Domoic acid is not harmful to certain sea animals that feed on Pseudo-nitzschia australis, including small fish such as sardines and anchovies. Larger predators including larger species of fish and crabs that feed on sardines and anchovies can become reservoirs for domoic acid. Filter feeders such as clams, mussels, and oysters can also accumulate domoic acid. Levels of domoic acid in an organism can decrease but the rate and concentration levels vary dramatically by species. For example, domoic acid levels in some species of mussels can decrease to safe levels within days, while levels of domoic acid in razor clams can remain elevated for weeks to months. The Food and Drug Administration safety threshold for domoic acid is 30 parts-per-million action level.

Repeated exposure to domoic acid or consuming a large quantity of contaminated seafood results in ASP. Symptoms include lethargy, disorientation, seizures, coma, and possible death. As a neurotoxin, domoic acid targets the brain, particularly the hippocampus which is responsible for memory. There are no medications to treat domoic acid poisoning directly. Treatments for ASP include administering fluids to help remove domoic acid from an infected animal or person. Long-term impacts of ASP include irreversible memory loss and the inability to form short term memories.

In November and December 1987, the first large scale outbreak of domoic acid poisoning through consuming contaminated mussels was recorded in Canada.¹⁷ In 1998, the first mammal exhibiting domoic acid poisoning was recorded at the Marina Mammal Center in Sausalito, California, just across the Golden Gate Bridge from San Francisco where over 400 sea lions suffered significant neurological symptoms or death.¹⁸ In 2015, an unprecedented postponement of the California commercial Dungeness crab fishing season was enacted due to dangerous levels of domoic acid as the result of a large scale algae bloom attributed to changing weather patterns.¹⁹

California Sea Lions

Sea lions feed on a variety of small fishes, such as anchovies and sardines, crabs, and clams. In San Francisco, they are a tourist attraction and can be seen lounging on the docks near Fisherman’s Wharf. As animals higher up the food chain, regular consumption of domoic acid contaminated sea creatures can lead to buildup of domoic acid in sea lion brains. Affected sea lions may exhibit symptoms of dizziness, vomiting, seizures, and loss of pregnancy.  Observations of erratic behaviors of sea lions, characterized by head weaving, are used as indicators of localized algae blooms. It is not practical nor possible to determine when and where toxic algae blooms will form. These sea lions are essentially canary birds in a coalmine, as they serve as warning signals for humans to avoid certain regions of coastline for fishing when increased numbers of sea lions behaving erratically, a symptom of domoic acid poisoning, are reported. 

Figure 4: Marine Mammal Center volunteers work to rescue a California sea lion.²⁰

The Marine Mammal Center maintains records of the number of sea lions with domoic acid poisoning along the Central California Coastline. Confidence intervals based on past data are used to make predictions on the expected number of live sea lion stranded on beaches, exhibiting symptoms, and requiring treatment at the center for suspected domoic acid poisoning. In 2015, projections expected between 43 and 86 sea lions to be stranded on beaches while exhibiting symptoms. Due to a large algae bloom, there were 229 stranded sea lions in 2015 in the same region.²¹ In 2020, reports of California sea lions exhibiting domoic acid poisoning in mid-May were earlier in the year than expected.²²

Paralytic Shellfish Poisoning (PSP)

Gonyaulacoid dinoflagellates are unicellular organisms that can develop algal blooms and dinotoxins. Saxitoxin is an example of a heat stable neurotoxin associated with PSP. Onset of symptoms can occur within minutes and may take up to a couple of hours after consuming contaminated seafood. Symptoms include tingling sensations in fingers, lips, mouth, and toes, followed by loss of muscle control in legs and arms, difficulty breathing, nausea, paralysis of muscles, including the lungs which can lead to death through suffocation. Death can occur in less than 30 minutes.²³ California has recorded 543 illnesses and 39 deaths attributed to PSP since 1903.²⁴ As with ASP, there are no medications that treat PSP directly. Treatments address symptoms and may include placing affected individuals on ventilators.