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division of radiation safety and environmental management

Marine Biotoxin Monitoring Program​​

The CDPH Shellfish Program monitors paralytic shellfish poisoning and domoic acid biotoxins in bivalve shellfish, covered in this page. Additional information on domoic acid in crustaceans (crabs and lobsters) is posted by the CDPH Food and Drug Branch.

Naturally occurring marine biotoxins are a year-round public health threat. Biotoxins are produced by certain species of microscopic algae, also called phytoplankton. The biotoxins can concentrate in filter-feeding bivalve shellfish and crustaceans that feed on shellfish. Human illness or death can occur from consuming toxic bivalve shellfish (mussels, clams, scallops, oysters) or crustaceans (crabs, lobster). Cooking the seafood does not destroy the toxins.

The biotoxins of concern in California are saxitoxins, which can cause paralytic shellfish poisoning (PSP), and domoic acid, which can cause Amnesic Shellfish Poisoning (ASP).

Please check for biotoxin advisories​ before harvesting or consuming recreationally harvested shellfish. CDPH issues advisories when biotoxin alert levels are exceeded. The advisories are lifted after multiple low or undetectable results are reported.

CDPH issues a mussel quarantine from May 1 to October 31 each year. The annual quarantine prohibits the recreational collection of mussels for human consumption. This quarantine is to protect the public during the high-risk period for biotoxins when the most historical deaths from PSP have occurred in California. 

The recreational shellfish advisories do not apply to commercially sold clams, mussels, scallops, or oysters from certified dealers. Shellfish sold by certified harvesters and dealers are subject to frequent mandatory testing to monitor for toxins.

CDPH also monitors for the naturally occurring phytoplankton species that can produce the toxins. Phytoplankton samples help inform where shellfish sampling is needed; no advisories are issued related to plankton abundance. Only a few species of phytoplankton produce toxins that accumulate in shellfish. The presence or absence of visible plankton bloom is not an indication of biotoxins in shellfish. 

The CDPH Marine Biotoxin Monitoring Program relies on volunteers and partnerships to collect the shellfish (mostly mussels) and plankton samples from the California coast. 

Shellfish Program Home Page

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