September 2023 Marine Biotoxin Monitoring Monthly Report

California Department of Public Health

Technical Report 23-30

January 10, 2024

Introduction

This report contains results from the California Department of Public Health (CDPH) monitoring programs for shellfish toxins and associated toxin-producing phytoplankton. Toxin concentration ranges are provided for the paralytic shellfish poisoning (PSP) toxins and for domoic acid, the latter associated with the syndrome called amnesic shellfish poisoning. Estimates are provided for the distribution and relative abundance of Alexandrium, the dinoflagellate that produces PSP toxins, and Pseudo-nitzschia, the diatom that produces domoic acid. This report also contains summary information for any quarantine or health advisory in effect during the reporting period. Finally, lists of participating agencies and volunteers for each monitoring effort are provided.

Map Notations

Please note the following conventions for the phytoplankton and shellfish biotoxin distribution maps:

(i) All estimates for phytoplankton relative abundance are qualitative, based on sampling effort and percent composition;

(ii) Only known toxin-producing species (e.g., seriata complex for Pseudo-nitzschia) are represented on the maps;

(iii) The relative abundance of Alexandrium and Pseudo-nitzschia are represented by icons that increase in size with increasing relative abundance as shown in the phytoplankton map key to the right.

(i) All toxin data are for mussel samples, unless otherwise noted;

(ii) All shellfish samples are assayed for PSP toxins; DA analyses are performed as needed (e.g., on the basis of detected blooms of the diatoms that produce DA or as part of a continuing surveillance effort);

(iii) Weekly PSP data are represented by four color-coded boxes as shown in the shellfish biotoxin map key to the right;

(iv) Domoic acid data is represented as four weekly color-coded circles overlayed on the PSP boxes.

Northern California Summary

Paralytic Shellfish Poisoning

Alexandrium was observed in 15 of the 49 northern California phytoplankton samples collected in September (Figure 1). This dinoflagellate was observed in samples from most coastal counties, and increase in distribution from the previous month. Alexandrium percent composition was elevated in samples from inside Humboldt Bay (3%, September 11), offshore of Noyo Harbor (6%, September 18), outer Tomales Bay (5%, September 11), and the Drakes Bay sentinel station (8%, September 17).

PSP toxicity was detected in shellfish samples from each coastal county between Del Norte and Marin, as well as Santa Cruz (Figure 2). All toxin concentrations were below the alert level.

Domoic Acid

Pseudo-nitzschia was observed in 19 of 49 phytoplankton samples collected in September (Figure 1). This diatom was observed in samples from each coastal county between Humboldt and Monterey, with the exception of Sonoma. The percent composition of Pseudo-nitzschia was elevated in samples from Hunter Rock (30%, September 28), inside Humboldt Bay (51%, September 25), and approximately 20 miles offshore of Bolinas in Marin County (10%, September 23). The cell mass of this diatom was significantly high inside Humboldt Bay, lower but still elevated at Hunter Rock, and insignificant in the offshore Marin sample.

Domoic acid was detected in a mussel sample from Hunter Rock (7.6 ppm, September 28) (Figure 2).

Phytoplankton Observations

A mix of diatoms and dinoflagellates were common along the northern California coast. The diatom Chaetoceros was common to abundant at Humboldt County sites, while the dinoflagellate Prorocentrum micans was common at sites between Mendocino and Santa Cruz counties. The dinoflagellate Akashiwo sanguineum was also common at the Point Arena Pier in Mendocino County.

The potentially harmful raphidophyte Heterosigma akashiwo was abundant inside San Francisco Bay at two sites in Alameda (70%, September 6); the cell mass was significant in both samples.

This month’s photos include the chain-forming diatoms Stephanopyxis and Bacteriastrum.

Southern California Summary

Paralytic Shellfish Poisoning

Alexandrium was observed in 11 of 60 phytoplankton samples collected in September (Figure 3). The percent composition of Alexandrium increased dramatically in outer Morro Bay (10%, September 5) and remained elevated at the mid-bay site (5%, September 11 and 18). Low numbers of this dinoflagellate were also observed in samples from the San Simeon Pier and offshore of Diablo Cove (San Luis Obispo County), offshore of the Palos Verdes peninsula (Los Angeles County), and in outer Agua Hedionda Lagoon and at Scripps Pier (San Diego County).

PSP toxicity continued to be detected in shellfish samples from San Luis Obispo County in September (Figure 4). The toxin concentration increased above the alert level in mussels from the Cal Poly Pier (80 µg/100 g, September 6) and continued to increase through at least September 18 (293 µg/100 g). Low levels of the PSP toxins were also detected in oysters from inner Morro Bay and at Montaña de Oro.

Domoic Acid

Pseudo-nitzschia was observed in seven of the 60 September samples (Figure 3). The relative abundance and distribution of this diatom declined compared to the previous month.

Domoic acid was not detected in any mussel or oyster samples in September (Figure 4).

Phytoplankton Observations:

Dinoflagellates dominated the phytoplankton assemblage along the southern California coast in September. Akashiwo sanguineum was abundant at the San Simeon Pier (64%, September 22) and common in mid Morro Bay. This unarmored dinoflagellate had been abundant at the Pismo Pier the previous month, but was replaced by Lingulodinium polyedrum and Prorocentrum micans in September (both at 35% on September 19). Lingulodinium polyedrum was also common to abundant in samples from numerous sites between San Luis Obispo and San Diego counties.

This month’s photos highlight the small, chain-forming diatom Skeletonema and the dinoflagellate Dinophysis acuminata.

Sampling Effort

The Marine Biotoxin Monitoring and Control Program, managed by the California Department of Public Health, is a state-wide effort involving a consortium of participating organizations, agencies, and volunteer samplers.

The phytoplankton sampling and observation element of the biotoxin monitoring program is a state-wide effort designed to detect toxin producing species of phytoplankton in ocean waters before they impact shellfish resources. The phytoplankton monitoring and observation effort can provide an advanced warning of a potential toxic bloom, allowing us to focus sampling efforts in the affected area before California's valuable shellfish resources or the public’s health is threatened.

Historically, the majority of shellfish toxicity episodes in California have originated along the open coast, occasionally moving into bays and estuaries. The shellfish sampling element of the program provides an early warning of shellfish toxicity by routinely assessing coastal resources for the presence of paralytic shellfish poisoning (PSP) toxins and domoic acid. Routine shellfish sampling is essential for protecting the public from these dangerous toxins.

For Information on Volunteering: Email redtide@cdph.ca.gov or call 510-412-4635

Phytoplankton Samplers

*A volunteer collecting a phytoplankton sample.*

Phytoplankton samples are primarily collected from coastal piers, although sampling can also be conducted from boat docks and offshore via vessel (kayak, boat). Samples are collected with a plankton net following our standard protocol. The sample bottle and sample collection form are placed in a shipping canister and sent to the CDPH laboratory in Richmond where program staff examine samples with light microscopy. CDPH provides all equipment and prepaid shipping containers.

Shellfish Samplers

Mussel samples are routinely collected at one or more representative sampling stations in each coastal county following our standardized protocol. Samplers collect 15-20 individuals and place the shellfish tissue in a sample bottle, which is immediately refrigerated, then frozen overnight. Samples are shipped in an insulated container via 24-hour courier to the department’s laboratory in Richmond for toxin analysis. All materials and shipping are provided by CDPH.

Quarantines, Health Advisories

The following is a list of recent Health Advisories and Quarantines for bivalve shellfish prior to October 1, 2023. For access to current advisories, please refer to the end of this report.

● The annual mussel quarantine on sport-harvested mussels began on May 1. The quarantine applies to all species of mussels that are recreationally harvested for human consumption along the California coast, including all bays and estuaries. During the quarantine, mussels may only be harvested for use as bait. The quarantine is in place to protect the public against poisoning that can lead to serious illness, including coma and death.

● On September 7 CDPH issued a health advisory warning consumers not to eat sport-harvested mussels, clams, or scallops from Mendocino County due to dangerous levels of the paralytic shellfish poisoning toxins in shellfish samples.

● On August 3 CDPH lifted the domoic acid shellfish advisory related to related to sport-harvested razor clams in Humboldt County.

● On August 1 CDPH lifted the domoic acid shellfish advisory related to related to sport-harvested mussels, scallops, and clams in Santa Barbara County.

● On July 28 CDPH issued a health advisory warning consumers not to eat sport-harvested mussels, clams, or scallops from San Mateo County due to dangerous levels of the paralytic shellfish poisoning toxins in shellfish samples.

● On July 14 CDPH issued a health advisory warning consumers not to eat sport-harvested mussels, clams, or scallops from San Luis Obispo County due to dangerous levels of the paralytic shellfish poisoning toxins in shellfish samples.

● On July 6 CDPH lifted the shellfish advisory related to sport-harvested razor clams in Del Norte County. The safety notification was issued on November 3, 2022 due to dangerous levels of naturally occurring domoic acid, also referred to as Amnesic Shellfish Poisoning. Razor clams have been continually tested and have now met the criteria for lifting the safety notification in Del Norte County. An advisory for razor clams in Humboldt County remains in effect.

On June 16 CDPH advised consumers not to eat sport-harvested mussels, clams, or scallops from Santa Barbara County due to the presence of dangerous levels of domoic acid in shellfish samples.

● On June 16 CDPH advised consumers not to eat sport-harvested mussels, clams, or scallops from Santa Barbara County due to the presence of dangerous levels of domoic acid in shellfish samples.

● On May 1 CDPH initiated the annual quarantine of sport-harvested mussels gathered along the California coast. The quarantine normally extends from May 1 through October 31, although elevated toxin levels can extend the quarantine period. This annual quarantine applies to all species of mussels that are recreationally harvested for human consumption along the California coast, including all bays and estuaries. The quarantine is in place to protect the public from poisoning that can lead to serious illness, including coma and death.

Paralytic Shellfish Poisoning Information:

Consumers of Washington clams, also known as butter clams (Saxidomus nuttalli), are cautioned to eat only the white meat. Washington clams can concentrate the PSP toxins in the viscera and in the dark parts of the siphon and can remain toxic for a long period of time. Persons taking scallops or clams, with the exception of razor clams, are advised to remove and discard the dark parts (i.e., the digestive organs or viscera). Razor clams (Siliqua patula) are an exception to this general guidance due to their ability to concentrate and retain domoic acid in the edible white meat as well as in the viscera.

PSP toxins can produce a tingling around the mouth and fingertips within a few minutes to a few hours after eating toxic shellfish. These symptoms can be followed by disturbed balance, lack of muscular coordination, slurred speech and difficulty swallowing. In severe poisonings, complete muscular paralysis and death from asphyxiation can occur.

Domoic Acid Poisoning Information:

Symptoms of domoic acid poisoning can occur within 30 minutes to 24 hours after eating toxic seafood. In mild cases, symptoms of exposure to this nerve toxin may include vomiting, diarrhea, abdominal cramps, headache and dizziness.

These symptoms disappear completely within several days. In severe cases, the victim may experience excessive bronchial secretions, difficulty breathing, confusion, disorientation, cardiovascular instability, seizures, permanent loss of short-term memory, coma and death.

Sport-harvester Information:

Any person experiencing any of these symptoms should seek immediate medical care. Consumers are also advised that neither cooking or freezing eliminates domoic acid or the PSP toxins from the shellfish tissue. These toxins may also accumulate in seafood species such as crab, lobster, and small finfish like sardines and anchovies.

Sportharvesters should only collect shellfish from areas that are not affected by a current health advisory or quarantine.

Contact the “Biotoxin Information Line” at 1-800-553-4133 or view the recreational bivalve shellfish advisory interactive map for a current update on marine biotoxin activity prior to gathering and consuming shellfish.