California HAB Bulletin: May 2021

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, suggesting most places are regularly 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 May, very high bloom probabilities were predicted far offshore for the northern and central coasts of California to the Santa Barbara Channel, while more confined to the nearshore zones of the Southern California Bight (and more towards the end of May). 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 'seriata' size class of Pseudo-nitzschia reached abundances not seen since 2017 at Santa Monica Pier (277,863 cells/L) and since 2019 at Newport Beach Pier (171,519 cells/L). The more nontoxigenic 'delicatissima' size class hit record levels at those sites as well -- highest levels since 2011 for both Santa Monica Pier (485,775 cells/L) and Newport Beach Pier (1,018,718 cells/L). The 'seriata' size class also exceeded the 10,000 cells/L bloom threshold at Cal Poly Pier at the end of the month. This is consistent with high nearshore bloom probabilities from C-HARM in the central coast and Southern California Bight regions. No bloom levels were observed, however, for either size class in May at Santa Cruz Wharf, which is inconsistent with the persistently elevated probabilities for Pseudo-nitzschia blooms throughout the Monterey Bay area in May. Given that the Santa Cruz Wharf sits within a well-known upwelling shadow in the northern portion of the Monterey Bay and is often decoupled from plankton dynamics in the rest of the bay, it is important to note the caveat that nearshore measurements of Pseudo-nitzschia at the Santa Cruz Wharf are often expected to differ from the realities offshore and from bay wide C-HARM predictions. The Relative Abundance Index (RAI) for the Pseudo-nitzschia "seriata" size class recorded by the California Department of Public Health (CDPH) reached moderate to very high levels (20-60%) from the Santa Barbara Channel (as in April) down to Palos Verdes in Los Angeles County, consistent with the records at Santa Monica Pier. Note that HABMAP observations for Stearns Wharf in Santa Barbara were not yet available for May 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 May with an increasing focus on the central coast, Sonoma County, Mendocino County, and Humboldt/Del Norte County coastlines. As the month progressed, zones of high pDA likelihood, or "hotspots," intensified and moved northward and more offshore along the central and north coasts as well as throughout the Southern California Bight (a reversal from April). HABMAP pDA data are so far only available for Santa Cruz Wharf in May, and for only the earliest part of the month, and indicate zero (or non-detectable) levels. Similar patterns were predicted for cellular domoic acid (cDA) risk as those for pDA, although with much lower probabilities in the Bight (southeast of the Santa Barbara Channel) early to mid month. Those cDA probabilities intensified to near 100% in the Santa Monica/San Pedro Bay area as well as for parts of the Orange County coastline. Relative to April, both pDA and cDA probabilities were intensified for much of the North Coast, which could indicate a real chance of greater toxicity for northern California. However, note that a razor clam health advisory that had been in effect since 2015 for Del Norte County due to domoic acid was finally lifted on May 3, 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 May was reported by The Marine Mammal Center (TMMC) on May 21 in Monterey County, suggesting that the high C-HARM probabilities for pDA and cDA in Monterey Bay were capturing a real hot spot, depending on where the animal was foraging when it acquired the DA; no other regions reported suspected DA toxicosis cases in May.

Alexandrium - CDPH did not observe any Alexandrium spp. at sites sampled in May, 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 May 2021

Probability of Particulate DA for May 2021

Probability of Cellular DA for May 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

Four water samples were collected at Santa Cruz Wharf in May. Molecular probes for toxigenic Pseudo-nitzschia in the "seriata" class are conducted for this site; Pseudo-nitzschia "seriata" was detected once (May 12) below the bloom threshold value. Alexandrium spp. were not detected. Domoic acid results are not yet available. 

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

Cal Poly Pier

Two water samples were collected at Cal Poly Pier in May. Pseudo-nitzschia "delicatissima" was detected only once (May 3) and was below the bloom threshold value. Pseudo-nitzschia "seriata" was detected twice (May 3, 10), with only May 10 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 May.

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

Santa Monica Pier

One water sample was collected at Santa Monica Pier in May. Pseudo-nitzschia "delicatissima" and Pseudo-nitzschia "seriata" were detected (May 3) well above the bloom threshold. Alexandrium spp. were not detected, and domoic acid results are not yet available. 

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

Newport Beach Pier

Four water samples were collected at Newport Beach Pier in May. Pseudo-nitzschia "delicatissima" and Pseudo-nitzschia "seriata" were detected on three occasions (May 3, 10, 17). All detections were above the bloom threshold except for "seriata" on May 17. Alexandrium spp. were not detected, and domoic acid results are not yet available.

The 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 May 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 May 1-31 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 47 of the 90 samples. Pseudo-nitzschia "seriata" was detected at "Common" density levels (using CDPH relative abundance index) on 7 occasions: May 3 (Port Hueneme Pier, 20% composition), May 9 (Point Dume, 20% composition), May 10 (Ventura, 30% composition), May 11 (Malibu Beach, 20% composition), May 12 (Santa Cruz Island, 11% composition) and twice on May 28 in the Santa Barbara area (Mohawk Reef, 15% composition; Naples Pt, 20% composition). Pseudo-nitzschia "seriata" was detected at "Abundant" density levels on May 9 (51% composition) and May 12 (60% composition), both in the Palos Verdes area. Alexandrium spp. were detected in 8 of the 90 samples. Alexandrium spp. were detected at "Present" density levels on 2 occasions: May 12 (Goleta Pier, 1% composition) and May 28 (Naples Pt in Santa Barbara, 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 six rehabilitation centers we received data for in the month of May, 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 May 2021.   

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

  • Monterey (TMMC)
    • May 21 - juvenile, male, 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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