California HAB Bulletin: April 2021

Be sure to also read the special Red Tide Bulletin: Spring 2020 

Pseudo-nitzschia - C-HARM tells us where conditions are suitable for species of the diatom Pseudo-nitzschia spp. (all size classes) to grow well and where they might be more likely to produce the deadly neurotoxin, domoic acid (DA). C-HARM now routinely predicts suitable habitat for Pseudo-nitzschia spp. throughout the state for, suggesting most places are routinely experiencing conditions conducive to growth and blooms throughout the year, with variability from month to month on where the centers of highest likelihood occur. In April, the focal point was central California to the Santa Barbara Channel and into the nearshore zones of the Southern California Bight, with probabilities waning dramatically in the southern most region around Orange and San Diego Counties as the month progressed. Given ongoing COVID-19 sampling restrictions and delays that continue to hamper our ability to acquire timely HABMAP observations from piers, not all piers are currently providing data, but we do know that the more toxigenic size class of Pseudo-nitzschia was at or well above the bloom threshold at Santa Monica Pier and Newport Beach Pier from mid to late April before dropping to zero by the end of the month; this is not entirely consistent with the very low probabilities in that area from mid to late April, however, some of the nearshore pixel probabilities remained high. HABMAP records for Santa Cruz Wharf show non-bloom levels of Pseudo-nitzschia in April even though bloom probabilities were periodically very high in the Monterey Bay area. The Relative Abundance Index (RAI) for the Pseudo-nitzschia "seriata" size class recorded by the California Department of Public Health (CDPH) reached moderate levels (20%) at Mohawk Reef in the Santa Barbara Channel nearshore zone but was generally low at all other sites sampled in the state. Note that HABMAP observations for Stearns Wharf in Santa Barbara were not yet available for April at the time of compiling this bulletin.

Moderate to very high C-HARM probabilities (50-100%) for particulate domoic acid (pDA) were predicted at different times for several sections of the California coastline in April with a focus on the central coast, Sonoma County and Mendocino County coastlines, and the northern parts of southern California. As the month progressed, zones of high pDA likelihood, or "hotspots," intensified and moved more offshore along the central coast near the Santa Barbara Channel, San Luis Obispo, Monterey Bay. That pattern reversed for southern California (Orange County and San Diego), and unlike in March, pDA probabilities were very low outside SF Bay. HABMAP pDA data are so far only available for Santa Cruz Wharf in April and show zero (or non-detectable) levels. Similar patterns were predicted for cellular domoic acid (cDA) risk as those for pDA, although often with more intensity, particularly for northern California (high probabilities, Mendocino County) and southern California (Orange County and San Diego). As in March, both pDA and cDA probabilities were high much of April in a narrow band along the North Coast, suggesting a possible return to more seasonal domoic acid problems in that region. However, a razor clam health advisory that has been in effect since 2015 for Del Norte County due to domoic acid was finally lifted, indicating that this population of organisms that holds onto (and accumulates) DA for long periods has finally started to purge toxins to a safe level for consumption. The only California Sea Lion stranding from suspected DA toxicosis in April was reported by The Marine Mammal Center (TMMC) in mid-April in Marin County (just north of San Francisco), a region that was a potential hot spot according to C-HARM and HABMAP sampling; no other regions reported suspected DA toxicosis cases in April.

Alexandrium - CDPH did not observe any Alexandrium spp. at sites sampled in April, consistent with HABMAP sampling, and there are no recreational shellfish advisories related to PSP at this time.

*Please note that HABMAP sampling, CDPH sampling, and marine mammal rescues have been greatly reduced in response to COVID-19 safety measures.

C-HARM Model

Probability of Pseudo-nitzschia Bloom for April 2021

Probability of Particulate DA for April 2021

Probability of Cellular DA for April 2021

Harmful Algal Bloom Monitoring & Alert Program (HABMAP) 

**HABMAP sampling resumed after being suspended in March 2020 in accordance with the Governor's stay at home order. However, COVID-19 safety protocols and sampling restrictions may continue to affect operations and delay results.**

Note that data for some stations are not shown because they are not yet recorded in the public HABMAP archive.

Differentiating Pseudo-nitzschia species by light microscopy is difficult. For this reason, Pseudo-nitzschia "seriata" does not refer to an actual species but rather the larger size class of Pseudo-nitzschia, which is generally a more toxigenic group of species. Alternatively, Pseudo-nitzschia "delicatissima" refers to the smaller size class that is generally non-toxigenic. The dashed line on the plots demarcates the 10,000 cells/L "bloom" threshold designated here for Pseudo-nitzschia populations only.

More information and data visualizations on the statewide HAB network and forecasting system can be found on the California HABMAP website and on the SCCOOS Harmful Algal Bloom page.  

Santa Cruz Wharf

Three water samples were collected at Santa Cruz Wharf in April. Molecular probes for toxigenic Pseudo-nitzschia in the "seriata" class are conducted for this site; Pseudo-nitzschia "seriata" was detected twice (April 14, 21) below the bloom threshold value. Alexandrium spp. and domoic acid were not detected. 

The Santa Cruz Wharf shore station is supported by CeNCOOS PI Raphael Kudela at UCSC.

Cal Poly Pier

Four water samples were collected at Cal Poly Pier in April. Pseudo-nitzschia "delicatissima" was detected only once (April 12) and was above the bloom threshold value. Pseudo-nitzschia "seriata" was detected on each occasion (April 5, 12, 18, 26), with only April 12 being above the threshold value. Alexandrium spp. were not detected and domoic acid results are not yet available. 

Cal Poly Pier shore station is supported by SCCOOS PI Ryan Walter and Ally Pasulka at Cal Poly. 

Stearns Wharf

No samples were collected at Stearns Wharf in April.

Stearns Wharf is supported by SCCOOS PI Mark Brzezinski and Libe Washburn at UCSB. 

Santa Monica Pier

Four water samples were collected at Santa Monica Pier in April. Pseudo-nitzschia "delicatissima" was detected on three occasions (April 5, 17, 24), all below the bloom threshold. Pseudo-nitzschia "seriata" was also detected on the same three occasions (April 5, 17, 24), with April 5 being above the threshold. Alexandrium spp. were not detected. Domoic acid results are not yet available. 

Santa Monica Pier shore station is supported by SCCOOS PI Rebecca Shipe at UCLA.

Newport Beach Pier

Three water samples were collected at Newport Beach Pier in April. Pseudo-nitzschia "delicatissima" and Alexandrium spp. were not detected on any occasion (April 5, 12, 19). Pseudo-nitzschia "seriata" was detected twice (April 5, 12), with the first being above the threshold value. Domoic acid results are not yet available.

Newport Beach Pier is supported by SCCOOS PI David Caron at USC.

Scripps Pier

Scripps Pier water samples are not available for April 2020 through April 2021.

Scripps Pier is supported by SCCOOS PI Melissa Carter and Clarissa Anderson at UCSD. 

CDPH observations for Pseudo-nitzschia "seriata" and Alexandrium spp.

Please note, starting in July 2019, CDPH moved to only reporting Pseudo-nitzschia of the seriata complex and not all Pseudo-nitzschia spp. as previously provided. 

From April 1-30 2021, water samples were collected by volunteers and sent to the California Department of Public Health (CDPH) for analysis. Pseudo-nitzschia "seriata" group was detected in 49 of the 87 samples. Pseudo-nitzschia "seriata" was detected at "Common" density levels (using CDPH relative abundance index) on 2 occasions: April 28 (Goleta Pier, 13% composition) and April 30 (Mohawk Reef in Santa Barbara, 20% composition). Alexandrium spp. were detected in 9 of the 87 samples. Alexandrium spp. were detected at "Present" density levels on 2 occasions: April 8 (Goleta Pier, 1% composition) and April 12 (Morro Bay Boat Launch, 1% composition).

You can view an interactive map and data table of CDPH data from January 2019 to present developed by SCCOOS below or you can also view CDPH Toxic Phytoplankton Observations Map with layers of Pseudo-nitzschia and Alexandrium spp. as well as other phytoplankton species observations (in the pop-up windows).

Data are provided by the California Department of Public Health, Environmental Management Branch.

Please email CDPH at for any potential marine HAB-related illness in humans.

CDPH and OEHHA Health Advisories 

May 3. The California Department of Public Health (CDPH) has lifted the August 2015 shellfish safety notification related to sport-harvested razor clams in Del Norte County.

April 30. The California Department of Public Health (CDPH) announced the annual quarantine of sport-harvested mussels gathered along the California coast.

For the latest closures and updates, please visit the CDPH Health Advisories page as a central location of information related to CDPH health advisories. Also available is a map showing the current CDPH Recreational Bivalve Shellfish Advisories (see below).

NEWS: The HAB-related illness workgroup has developed a new webpage for marine HAB-related illness tracking work ( 

California Marine Mammal and Seabird Strandings from Suspected DA Toxicosis

Domoic acid (DA) is a potent neurotoxin produced by some diatom species of the genus Pseudo-nitzschia. Species exposed to DA can result in seizures, epilepsy, cardiomyopathy, and death depending upon the ingested dose. DA toxicosis commonly occurs in California Sea Lions (Zalophus californianus), presumably due to a combination of foraging behavior and seasonal movements. The Marine Mammal Center (TMMC), Channel Islands Marine Wildlife Institute (CIMWI), California Wildlife Center (CWC), Marine Mammal Care Center Los Angeles (MMCC-LA), Marine Animal Rescue (MAR), the Pacific Marine Mammal Center (PMMC), and SeaWorld act like an emergency room by working to rescue and rehabilitate sick and injured marine mammals, seabirds, and sea turtles. 

Among the seven rehabilitation centers we received data for in the month of April, 1 marine mammal stranding presented with symptoms of domoic acid toxicosis. 

The CIMWI, CWC, PMMC, MMCCLA, and SeaWorld did not record any strandings due to suspected domoic acid in April 2021.   

April strandings due to suspected DA toxicosis occurred in the following counties:

  • Marin (TMMC)
    • April 19 - subadult, female, California Sea Lion 

At this time we do not have data from the North Coast Marine Mammal Center.  

Contacts if you find a LIVE stranded animal

Contacts if you find a DEAD stranded animal

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