Recent reports of a "red tide" in Kachemak Bay have once again caused confusion and concern among residents and visitors looking to harvest clams and mussels for a delicious wild Alaska seafood meal. Red tides can be associated with Paralytic Shellfish Poisoning or PSP, which is an illness caused by eating poisoned shellfish such as bivalve mollusks primarily clams, oysters, and mussels.
Microscopic single-celled phytoplankton called dinoflagellates, of the genus Alexandrium, can produce PSP toxins. Toxic outbreaks often are associated with algal blooms that cause a red-brown discoloration of the water; however, the color of the water is not a reliable indicator of levels of toxic algae in the water. It is important to note that most species of algae or phytoplankton are not harmful and do not produce toxins.
In Alaska, PSP-related blooms tend to be seasonal, usually occurring in the late spring and summer. However, PSP has been identified in shellfish during other times of the year, as well; in these cases, it is likely caused by the PSP toxins remaining in the shellfish for long periods past the bloom. Using days as an indicator to determine when shellfish are safe to eat after a known toxic bloom is unreliable and not recommended, since shellfish may be exposed to repeated bloom events.
Bivalves are filter-feeders, meaning they draw in seawater and then filter out the plankton for food. As they digest Alexandrium cells, the PSP toxin is released into their digestive system and subsequently distributed throughout the shellfish.
Although it is not dangerous to the various types of shellfish that eat the algae, once concentrated, the PSP toxin can be lethal to those that eat further up the food chain including humans who can get PSP by eating raw or cooked contaminated shellfish. Note: PSP is water soluble, and cooking will leach toxin from the tissues of contaminated shellfish into a broth. This toxicity cannot be cooked out.
The PSP toxin (Saxitoxin) is considered to be 1,000 times more lethal than cyanide. Within minutes and up to a few hours after ingesting PSP-contaminated shellfish, the signs and symptoms can appear. Initial symptoms are generally mild, beginning with tingling and numbness of the lips, face and neck. Numbness may continue into the arms and legs, followed by headache, dizziness, nausea, diarrhea, disorientation and muscular un-coordination. In cases of severe poisoning, symptoms include muscle paralysis, respiratory difficulty, dry mouth, throat constriction, sweating, rapid heartbeat, difficult or loss of speech, and brain stem dysfunction. When this happens, death may occur quickly.
There is no antidote for Saxitoxin; however, if given immediate treatment, the illness could run its course in 12 to 48 hours. Immediate treatment includes inducing vomiting and transporting a person to the nearest medical facility that can provide respiratory support.
Shellfish products sold in seafood markets are certified PSP-free. However, shellfish harvesters must ensure a beach is safe from PSP prior to collecting and eating shellfish. Testing for PSP is currently done by the Department of Environmental Conservation, Division of Environmental Health, on those beaches in Southcentral Alaska that have a commercial shellfish harvest.
Several beaches within Kachemak Bay and Cook Inlet are monitored for PSP, including Halibut Cove Lagoon, Jakolof Bay, Kasitsna Bay (MacDonald Spit), Tutka Bay, Chugachik Island, Sadie Cove, Polly Creek and Crescent River. Clam Gulch-Anchor Point beaches are not monitored for PSP.
The public is invited to learn more about PSP from Alaska Sea Grant's Marine Advisory Program aquaculture specialist Ray RaLonde, who will be giving a presentation entitled "Consuming Shellfish Safely" at noon Friday at the Alaska Islands and Ocean Visitor Center.
Terry Thompson is the education coordinator at the Kachemak Bay Research Reserve.
