May 2023 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 5 of 61 northern California phytoplankton samples collected in May (Figure 1). This dinoflagellate was present (2%) in a May 24 sample from the Santa Cruz Wharf and rare (<1%) in samples from inner Humboldt Bay (May 8), the Bodega Harbor sentinel station (May 17), and two sites offshore of Santa Cruz (May 15). All five samples had a low cell mass.
Low levels of PSP toxins were detected in mussels from two locations in May (Figure 2). Sentinel mussels from Santa Cruz Wharf contained 46 µg/100 g (May 24 and 31) and wild mussels from Wilson Creek (Del Norte County) contained 41 µg/100 g (May 22).
Domoic Acid
Pseudo-nitzschia sp..
Pseudo-nitzschia was observed in 40 of 61 phytoplankton samples (Figure 1). There was a significant increase in the percent composition of this diatom at several sites between San Mateo and Santa Cruz counties. Pseudo-nitzschia was abundant in samples from the Santa Cruz Wharf (60%, May 7) and in samples collected by the Applied California Current Ecosystem Studies (ACCESS) project offshore of San Mateo County (50%, May 12) and at two sites offshore of Santa Cruz County (71% and 58% on May 15). The cell mass was slightly elevated in the Santa Cruz Wharf sample and low in all other samples.
Three razor clam samples collected by the Tolowa Dee-ni’ Nation at Point St. George (Del Norte County) on May 7 contained varying levels of domoic acid, all below the alert level (17, 9.6, and 5.6 ppm). Three follow-up clam samples were collected at the same site on May 19 by volunteer Ken Graves; one sample exceeded the alert level (20 ppm), one contained a low concentration of domoic acid (9.5 ppm), and the third sample was below the reporting limit (<2.5 ppm). A third set of clam samples was collected on May 20 by the Tolowa Dee-ni’ Nation: all were below the alert level (17, 14, and 9.5 ppm).
Two razor clam samples were collected on May 10 at Clam Beach (Humboldt County) by volunteer Jack Foster: one sample was well above the alert level (36 ppm) and one was just below (18 ppm). Six follow-up samples were collected on May 22, with two samples exceeding the domoic acid alert level (23 and 22 ppm), two samples below the alert level (both 13 ppm), and two samples below the reporting limit.
Domoic acid was not detected in any other shellfish samples in May.
Phytoplankton Observations
Diatoms dominated the northern California phytoplankton assemblage in May. Chaetoceros was ubiquitous between Del Norte and Monterey counties, being observed at bloom levels at Hunter Rock (Del Norte County) on May 8. Thalassiosira was common to abundant at many sites between Del Norte and Marin counties, while Skeletonema was common to abundant at a number of sites between Marin and Monterey counties. High cell masses of the latter diatom, indicative of a bloom, were observed in samples from the Bodega Harbor sentinel station (May 17), in outer Tomales Bay (May 9 and 15), and at Pillar Point Harbor (May 13).
This month’s photos highlight two diatoms: the single-celled Pleurosigma and the chained Asterionellopsis.
Southern California Summary
Paralytic Shellfish Poisoning
Alexandrium sp.
Alexandrium was observed in 5 of 53 phytoplankton samples in May (Figure 3). While the frequency of occurrence declined from observations in April, the distribution increased northward to San Luis Obispo County. The percent composition of Alexandrium was slightly elevated in samples from Goleta Pier (3%) in Santa Barbara County and inside San Diego Bay (3%) in San Diego County; the cell mass was low in all samples.
Low concentrations of PSP toxins were detected in mussel samples from several locations (Figure 4): Goleta Pier (37 µg/100 g on May 3 and 17), an aquaculture lease just offshore of Santa Barbara (40 and 42 µg/100 g on May 8 and17, respectively), and at Mussel Shoals in Ventura County (38 µg/100 g on May 9).
Domoic Acid
Pseudo-nitzschia sp.
Pseudo-nitzschia was observed in 36 of the 53 samples, representing all but two sites sampled in May (Figure 3). The percent composition declined at most sites between Orange and San Diego counties compared to observations in April, but remained elevated at sites between Los Angeles and Santa Barbara counties. Pseudo-nitzschia increased at all Santa Barbara sites and was abundant (61%), with a slightly increased cell mass, at Scorpion’s Anchorage on Santa Cruz Island. The cell mass was also noticeably elevated in a May 11 sample from Santa Monica Bay (station 3501 of the City of Los Angeles Environmental Monitoring Division).
Domoic acid was not detected in any mussel or oyster samples in May (Figure 4).
Phytoplankton Observations:
A mix of diatoms and dinoflagellates was observed along the southern California coast. Common diatoms included Chaetoceros, Skeletonema, Thalassiosira and Thalassionema. The dinoflagellate Lingulodinium polyedrum was common offshore of Diablo Cove in San Luis Obispo County. Prorocentrum micans was common to abundant at numerous sites between Santa Barbara and San Diego counties, with elevated cell masses at most sites. Ceratium divaricatum was common at several sites between Los Angeles and San Diego counties.
This month’s photos highlight two dinoflagellates: Ceratium lineatum, observed in 13 of the 53 southern California samples, and the much larger Noctiluca scintillans (seen with Prorocentrum micans in the background); Noctiluca is a bioluminescent red tide species that is also heterotrophic.
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 Health Advisories and Quarantines for bivalve shellfish prior to June 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 January 9, 2023, CDPH rescinded the advisory for sport-harvested mussels, scallops, and most types of clams in Humboldt County. A domoic acid advisory for razor clams in Humboldt County remains in effect.
● On December 12 CDPH rescinded the advisory warning consumers not to eat sport-harvested mussels, scallops, and clams in San Mateo, Monterey, and San Luis Obispo counties due to the detection of dangerous levels of paralytic shellfish poisoning (PSP) toxins. Testing demonstrated that PSP toxins had decreased to safe or undetectable levels for bivalve shellfish in these areas. The PSP shellfish advisory for Humboldt County remained in place.
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.
