May 2024 Marine Biotoxin Monitoring Monthly Report
California Department of Public Health
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 sp.
Alexandrium was observed in four of the 50 northern California phytoplankton samples collected in May (Figure 1). Low numbers of this dinoflagellate were observed in samples from northern Sonoma County (May 29) and two sites offshore of Marin County. The latter two samples with Alexandrium are noteworthy as both were collected a considerable distance offshore, in the Greater Farallones National Marine Sanctuary, by the Applied California Current Ecosystem Studies (ACCESS) project. A May 20 sample was collected over 20 miles west of Pt. Reyes and a May 24 sample was collected approximately 10 miles northwest of Pt. Reyes. Alexandrium cell mass was slightly elevated in the Sonoma Kashia Coastal Reserve sample but low in all others.
Low concentrations of PSP toxins were detected the latter two weeks of May at the Drakes Bay sentinel mussel station and at the Santa Cruz Wharf the latter three weeks of the month (Figure 2).
Domoic Acid
Pseudo-nitzschia sp.
Pseudo-nitzschia was observed in 41 of 50 phytoplankton samples collected in all northern California counties except Monterey (samples were not available at the latter county; Figure 1). The relative abundance of Pseudo-nitzschia increased significantly at several locations in May compared to the previous month. This diatom was common in samples from Del Norte County, the Drakes Bay sentinel mussel station, and in samples collected offshore of Marin, San Francisco, and San Mateo counties by the ACCESS project. The cell mass of Pseudo-nitzschia was elevated at most of these sites, most significantly in the samples from Hunter Rock and Wilson Creek (Del Norte County) and the samples collected offshore of Marin, San Francisco, and San Mateo counties.
Alert levels of domoic acid were detected in razor clams from Crescent Beach in Del Norte County and Moonstone Beach in Humboldt County (Figure 2). Of the three Crescent Beach clam samples collected on May 11 by volunteer Ken Graves, two exceeded the alert level (31 and 20 ppm) and one was below (8.5 ppm). The Moonstone Beach razor clam sample, collected on May 10 by volunteer Kirk Yonker, exceeded the alert level (26 ppm).
Domoic acid was not detected in any mussel or oyster samples collected in May (Figure 2).
Phytoplankton Observations
The diatoms Skeletonema and Chaetoceros were common to abundant at sites between Del Norte and San Mateo counties, in addition to one interior county (Contra Costa) bordering San Francisco Bay. Significantly high cell masses of Chaetoceros, indicative of a bloom, were observed at the Drakes Bay sentinel mussel station, in outer Tomales Bay, and approximately 35 miles offshore of San Francisco. The diatoms Eucampia, Lauderia, and Thalassiosira were common inside Monterey Bay at the Santa Cruz Wharf; by the end of the month the dinoflagellate Lingulodinium polyedrum was common at this site.
This month’s photos highlight the diatoms Skeletonema and Corethron. The latter diatom has the unique ability to move the silica spines that are arranged in a ring at both ends of the cell.
Southern California Summary
Paralytic Shellfish Poisoning
Alexandrium sp.
Alexandrium was observed in 19 of 51 phytoplankton samples collected in May (Figure 3). This increase in the frequency of observations was most notable at sites between Los Angeles and San Diego counties. There was a significant increase in the relative abundance of this dinoflagellate in samples from Orange and San Diego counties, although the cell mass was low at all sites.
Low concentrations of PSP toxins were detected in mussel samples from outer Agua Hedionda Lagoon and inside San Diego Bay by the last week of May (Figure 4).
Domoic Acid
Pseudo-nitzschia sp.
Pseudo-nitzschia was observed in 28 of the 51 May samples (Figure 3). There was a significant increase in the relative abundance of this diatom at sites in San Luis Obispo, Santa Barbara and San Diego counties. Pseudo-nitzschia was abundant in samples from the Goleta Pier (68%, May 15) and Mohawk Reef (70%, May 17) and common at sites in San Luis Obispo, Ventura, Los Angeles, and San Diego counties. Despite the increases in percent composition at numerous locations, the cell mass was low in all samples.
Domoic acid was not detected in any mussel or oyster samples in May (Figure 4).
Phytoplankton Observations:
Diatoms were common to abundant in samples from Santa Barbara and Ventura counties. Thalassiosira was abundant at Naples Pt. (70%, May 17), Rhizosolenia was common at the Goleta Pier (35%, May 29), and Chaetoceros was common (25%, May 2) at the Port Hueneme Pier.
A mix of diatoms and dinoflagellates were common to abundant at sites between Los Angeles and San Diego counties. The diatom Chaetoceros was common offshore of Point Dume (20%, May 12) and inside Bolsa Chica Lagoon (20%, May 10), while Rhizosolenia was abundant offshore of Palos Verdes (55%, May 31). The dinoflagellate Prorocentrum micans was common throughout this range, while Akashiwo sanguinea and Lingulodinium polyedrum were common to abundant at sites in Orange and San Diego counties. Slightly elevated cell masses were observed for P. micans in Santa Monica Bay and for L. polyedrum at Pacific Beach Pier.
Included in this month’s photos are the chain-forming diatom Thalassiosira and the dinoflagellate Prorocentrum micans.
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
A Sonoma County mussel bed.
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 Quarantines and Health Advisories for bivalve shellfish prior to June 1, 2024. For access to current advisories, please refer to the end of this report.
The annual mussel quarantine on sport-harvested mussels is scheduled to begin 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 May 2, 2024, CDPH issued a health advisory warning consumers not to eat sport-harvested razor clams from Humboldt County due to dangerous levels of domoic acid in razor clams, which can cause Amnesic Shellfish Poisoning.
Paralytic Shellfish Poisoning Information:
Consumers of Washington clams, also known as butter clams (Saxidomus nuttalli), are cautioned to eat only the white meat, regardless of the current quarantine status. 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.
