August 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 7 of the 32 northern California phytoplankton samples collected in August (Figure 1). The range of Alexandrium observations was similar to the previous month, however the number of sites containing this dinoflagellate decreased. The percent composition of Alexandrium was significantly elevated in samples from the Santa Cruz Wharf (15% and 10%, August 14 and 21, respectively). The cell mass was low at all sites.
PSP toxicity exceeded the alert level in sentinel mussels from the Santa Cruz Wharf (664 µg STX eq./100g) by August 21 (Figure 2). Low concentrations of these toxins were detected in mussel samples from Del Norte, Humboldt, Mendocino, Sonoma, Marin, Santa Cruz, and Monterey counties.
Domoic Acid
Pseudo-nitzschia sp.
Pseudo-nitzschia was observed in 13 of 32 phytoplankton samples, representing numerous sites between Del Norte and Santa Cruz counties (Figure 1). The distribution of Pseudo-nitzschia was identical to the previous two months, with a significant increase in the relative abundance at sites in Del Norte and Humboldt counties: Hunter Rock (30%, August 22); Gold Bluffs Beach (70% and 68%, August 13 and 19, respectively); Trinidad Pier (98%, August 21); and inner Humboldt Bay (80%, August 26). Pseudo-nitzschia also remained common at the Drakes Bay sentinel mussel station (15%, August 8).
Domoic acid concentrations remained above the alert level, and increased noticeably, in razor clam samples from Crescent Beach, Del Norte County and Clam Beach, Humboldt County (Figure 2). All three clam samples collected from Crescent Beach by CDPH volunteer Chris Hegnes on August 20 exceeded the alert level (75, 120, and 120 ppm). The Tolowa Dee-ni’ Nation sampled the same beach one day later, with all three clam samples exceeding the alert level for domoic acid (60, 61, and 64 ppm). CDPH volunteer James Hartman collected razor clam samples from Clam Beach on August 3, with all three samples exceeding the alert level (65, 78, and 82 ppm).
Several mussel samples also contained domoic acid, with concentration above the alert level in samples from outer Humboldt Bay (23 and 21 ppm, August 6 and 26, respectively). Low concentrations of domoic acid were also detected in mussel samples from Hunter Rock in northern Del Norte County (3.1ppm, August 22), Trinidad Head in norther Humboldt County (4.7 ppm, August 8), and inner Humboldt Bay (5.5, 10, and 5.8 ppm, August 5, 19, and 26, respectively). All other mussel and oyster samples analyzed for domoic acid were below the method detection limit (Figure 2).
Phytoplankton Observations
A mix of diatoms and dinoflagellates was observed along the northern California coast. The diatom Skeletonema was common to abundant inside Humboldt Bay, and Eucampia was common inside Tomales Bay. The bioluminescing dinoflagellate Noctiluca was abundant at Hunter Rock (50%, August 20). Another dinoflagellate, Akashiwo sanguinea, was common to abundant in outer Tomales Bay. The raphidophyte Heterosigma akashiwo, a harmful algal bloom species that can cause fish kills, was abundant in a sample from the Seaplane Lagoon on the eastern shore of San Francisco Bay (90%, August 16); the cell mass was significantly elevated, indicative of a bloom.
This month’s photos highlight two rare diatoms. Melosira was observed at four sampling sites, all protected bays (Humboldt and the Richmond marina in San Francisco Bay). Thalassiothrix was present in Humboldt Bay and at the Drakes Bay sentinel mussel station.
Southern California Summary
Paralytic Shellfish Poisoning
Alexandrium sp.
Alexandrium was observed in 7 of 42 phytoplankton samples collected in August (Figure 3). This dinoflagellate continued to be observed in low numbers in samples from the Scripps Pier in La Jolla, and in elevated numbers in mid Morro Bay (10%, August 26).
Low concentrations of PSP toxins were detected in oyster samples from inner Morro Bay (39 and 52 µg STX eq./100g, August 26 and 28, respectively; Figure 4).
Domoic Acid
Pseudo-nitzschia sp.
Pseudo-nitzschia was observed in 22 of the 42 August samples (Figure 3). This diatom remained common in mid Morro Bay (40% and 10%, August 5 and 26, respectively); the cell mass was significantly elevated for the former sample. Pseudo-nitzschia continued to be abundant offshore of Diablo Cove (65% and 89%, August 6 and 26), with elevated cell mass. This diatom was also common inside San Diego Bay (10%, August 7).
An alert level of domoic acid was detected in a mussel sample from an aquaculture facility offshore of Santa Barbara on August 5 (23 ppm), declining below the detection limit by August 11. This toxin was not detected in any other shellfish samples (Figure 4).
Phytoplankton Observations:
There was a mix of diatoms and dinoflagellates along the southern California coast. The diatom Chaetoceros was common in samples from Santa Barbara to San Diego counties and abundant offshore of Pt. Dume, Los Angeles County (76%, August 3; low cell mass). The dinoflagellate Akashiwo sanguinea was abundant at the Cayucos Pier (58%, August 30), and the dinoflagellate Lingulodinium polyedrum was common in samples from the Manhattan Beach Pier and Bolsa Chica Lagoon.
Included in this month’s photos are a typically rare dinoflagellate and a very rare diatom. The dinoflagellate Prorocentrum scutellum was observed in 2 samples, while the diatom Striatella was only observed in mid Morro Bay.
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 September 1, 2024. For access to current advisories, please refer to the end of this report.
● May 1, 2024, the annual mussel quarantine on sport-harvested mussels began. 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.
● On July 3 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Humboldt County due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.
● On July 16 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Del Norte County due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.
● On July 18 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Santa Cruz and Monterey counties due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.
● On July 19 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Sonoma County due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.
● On July 26 CDPH issued a health advisory warning consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops, from Marin County due to dangerous levels of paralytic shellfish poisoning (PSP) toxins in recent samples.
● On August 8 CDPH issued a health advisory warning consumers not to eat advising consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops from Santa Barbara County due to dangerous levels of domoic acid in recent samples.
● On August 9 CDPH issued a health advisory warning consumers not to eat advising consumers not to eat sport-harvested bivalve shellfish, including mussels, clams, or scallops from Humboldt County due to dangerous levels of domoic acid in recent samples.
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.
