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Food and Drug Branch

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Main Telephone:

(800) 495-3232




Address (Courier Delivery):

California Department of Public Health - Food and Drug Branch

1500 Capitol Ave, MS 7602

Sacramento, CA 95814


Address (Non-Courier Delivery):

California Department of Public Health - Food and Drug Branch

P.O. Box 997435, MS 7602

Sacramento, CA 95899

Phytoplankton Monitoring Program

The CDPH Marine Biotoxin Program coordinates a volunteer-based monitoring effort for toxic phytoplankton along the entire California coastline. Interactive map layers provide information on our weekly data for the distribution and relative abundance of toxin-producing phytoplankton along the California coast. The following information provides an overview of the program and an explanation of why phytoplankton monitoring is an important tool for public health protection.


Phytoplankton are single-celled algae that are the base of the marine food chain. The vast majority of marine life in our coastal waters could not exist without these naturally-occurring microscopic plants.  There are hundreds of species of phytoplankton in the ocean, and the vast majority are nontoxic. A small number of species are known to produce toxins that can accumulate in filter-feeding organisms, especially bivalve shellfish like mussels, oysters, clams, and scallops. These toxins can also accumulate in small fish like anchovies and sardines, as well as in crustaceans like crab and lobster that may feed on other species that contain these toxins. Humans, as well as marine mammals and seabirds, can be harmed by these nerve toxins when dangerous levels accumulate in these seafood items. There are many categories of phytoplankton, of which dinoflagellates and diatoms are the most important with respect to marine toxins along the California coast.


Dinoflagellates are plants that can swim via their two flagella. As a result they can actually migrate vertically in the water column. When conditions are favorable, one or more populations of dinoflagellate may begin growing exponentially, resulting in millions of cells per liter of seawater. This 'bloom' can result in a phenomenon called a red tide. The vast majority of red tides along the California coast are produced by nontoxic species of dinoflagellates.

One genus of dinoflagellate, Alexandrium, is responsible for producing the PSP toxins. Alexandrium rarely blooms, so it is not safe to assume that the absence of a red tide means that shellfish in the area are safe to harvest and consume. Although Alexandrium rarely forms visible blooms, the toxins it produces are so potent that only a couple hundred cells per liter are required to result in dangerous levels of paralytic shellfish poisoning toxins in shellfish.


The group of phytoplankton called diatoms are single-celled and chain-forming algal cells with silica cell walls. Diatoms were not known to produce neurotoxins until a large-scale poisoning episode occurred in 1987 in eastern Canada. Over two hundred persons were made ill and four died as a result of mussel consumption in Prince Edward Island, a productive commercial shellfish growing area. Others suffered permanent neurological damage (for example, a permanent loss of short-term memory capabilities). The investigation by Canadian researchers and government scientists discovered the toxin, domoic acid, and the source of the toxin: a chain-forming diatom that is a common member of the phytoplankton community in many parts of the world. The syndrome caused by domoic acid was termed ‘Amnesic Shellfish Poisoning’ (ASP).

The diatom genus responsible for producing domoic acid is named Pseudo-nitzschia. Unlike Alexandrium, Pseudo-nitzschia is often observed in low numbers along the California coast. This diatom can also increase in numbers rapidly, producing blooms of millions of cells per liter and dominating the phytoplankton community for extended periods of time.

Program History

As mentioned previously, California has had a long-standing awareness of the dangers of paralytic shellfish poisoning and has relied on an extensive shellfish monitoring program to detect the presence of the potent toxins responsible for this syndrome. In the fall of 1991 another natural toxin was identified along the California coastline. An investigation into the deaths of hundreds of seabirds in Monterey Bay led to the identification of domoic acid as the cause. This neurotoxin was not previously known to exist anywhere along the west coast of the U.S. Domoic acid was identified in the anchovies and sardines on which the seabirds had been feeding. Further investigation discovered an abundance of the diatom Pseudo-nitzschia in the stomachs of the fish. Analysis of the fish gut contents revealed high concentrations of domoic acid. Although this toxin is less potent than the PSP toxins, it has become of increasing concern because the blooms of diatoms that produce this toxin have been of greater frequency and longer duration than most PSP events over the past 10 years. In addition, domoic acid has had dramatic impacts on marine mammal and seabird populations along the coast. These wildlife impacts have raised the public’s awareness of marine biotoxins in general and can provide valuable information to government scientists and university researchers.

Because of the threat of a new toxin, domoic acid, the presence of multiple toxic species along the California coast, and the apparent global increase in phytoplankton blooms in general and the increase in magnitude and geographic distribution of toxic blooms in particular, CDPH developed a volunteer-based phytoplankton monitoring program. This volunteer-based effort, the first statewide effort in the U.S., is one of several elements of CDPH’s effort to protect the public from these potentially deadly neurotoxins.

Phytoplankton Monitoring in California

The Phytoplankton Monitoring Program was officially launched in January 1993 when the first volunteer sample arrived at the CDPH laboratory. The first volunteers were existing program participants in the Shellfish Monitoring Program and local concerned citizens. Over the years the number and diversity of program participants has increased and includes local public health agencies, municipal utilities, K-12 school groups, university researchers and students, local environmental groups, educational nonprofit organizations, marine animal rescue centers, involved citizens, and many others. During 2014 there were 85 active volunteers collecting 1975 samples at 161 different locations. Over the first 20 years of the program there have been over 29,000 samples collected! This is a true testament to the dedication and importance of everyone who has participated in this program over the years.

What Volunteers Do

A phytoplankton net and rope is provided to all program participants, unless they happen to have access to one already. The net is made of a very fine and fragile nylon mesh: the mesh size is 20 micrometers, which is small enough to capture our toxin-producers and most other species present. The net is gently lowered into the water via the attached rope and allowed to sink to a depth of 10 to 50 feet, depending on the sampling location. The loose end of the rope is always secured to the pier or other structure to avoid losing it! The net is slowly retrieved and, as it reaches the surface, allowed to descend to the sampling depth again. We recommend three to five of these vertical net tows, depending on the sampling depth and the density of cells present that day. Following the final tow, the net is retrieved and the sampling bucket at the bottom of the net is detached. The contents of the sampling bucket are poured into the sampling bottle provided, which contains a small amount of preservative. The sample is then placed in the mailing canister along with the completed laboratory sample submission form, which contains the relevant sampling information (date, time, location, depth, etc.). The canister can then be sent to our laboratory via the U.S. Postal Service (postage is prepaid by CDPH).

What We Do

All samples arriving at CDPH are examined with light microscopy for the presence of the toxin-producing species. Additional information is recorded on other common, non-toxic species to help evaluate long-term trends in species composition and shifts in dominant groups (diatoms versus dinoflagellates). The field and lab observations provide a valuable snapshot of current trends in the phytoplankton community. This information is immediately used as necessary to guide additional sample collection in areas of concern. Over the years there have been numerous occasions in which the phytoplankton observations alerted program scientists to the early stages of a toxic bloom. Subsequent focus on the affected region revealed the presence of toxin and allowed CDPH to alert the public via a health advisory press release or to close a commercial shellfish growing area to prevent toxic seafood from entering the marketplace. In fact, many of the certified shellfish growers in California voluntarily collect phytoplankton samples and conduct the field observations because this valuable information helps them manage their harvest activities to ensure the safety of their product. Finally, the laboratory identifications and the volunteers’ field observations are recorded in the program database for subsequent reporting and analysis. Each participant's contribution is essential to piecing together a picture of the distribution of toxic and nontoxic phytoplankton along the California coast.

How to Get Involved

Despite the wonderful efforts of all our program participants there are still many areas of the California coast that do not have adequate sampling effort. CDPH is always interested in having new volunteers join the Phytoplankton Monitoring Program, especially if it is in an area that needs additional coverage. CDPH provides the necessary training and equipment for collecting and shipping samples at no cost to the volunteer. Some volunteers, typically those with a science background or a keen interest in phytoplankton, are trained to also conduct the microscopic observations of the samples they collect. This information is emailed or faxed to the program and a portion of the sample is also submitted. This allows CDPH biologists to check the volunteer’s accuracy in identifying the phytoplankton species present, which in turn allows us to provide feedback to help improve their skills and knowledge. The program also provides training materials to help in the identification process. To learn more about this program and opportunities to volunteer you can send an email to or call 510-412-4635.

Benefits of Volunteering

All of our program participants are added to an email distribution list to receive periodic informal updates on observations, trends, and detection of toxins along the California coast based on the volunteer monitoring effort. In addition, a more formal monthly report is distributed to everyone once the data has been compiled and validated. The monthly reports contain maps of toxigenic phytoplankton distribution and toxin distribution at all sampling sites. In addition, the monthly reports contain tables listing the program participants that provided samples or field identifications during that month. An annual report is also produced that summarizes the events and sampling effort of the past year.

Of course the real benefits to volunteering are the intangible ones. You will know that your efforts are important to a real-time public health protection program. Phytoplankton sampling and field observations also provide a way to get connected to your local ocean environment. The phytoplankton species composition will change with changing environmental conditions (for example, wind intensity and direction, water temperature), so each sample can bring something new. And you can interact with program biologists to have questions answered or to get advice on sources of additional information on a particular related topic.

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