| History | Biological Sketch | Current Monitoring and Response | PSP Database | Future Direction |
PSP Informational Brochure

Information About Red Tide  pdf format of Information About Red Tide
file size 1MB


Red Tide, PSP, toxic phytoplankton; whatever name is given them from a list of over sixty marine biotoxins, they spell trouble wherever they occur. Throughout history, they have made their presence known in every ocean and sea on the planet. In ancient Egypt, the historical note of "and all the waters were turned to blood" was testament to the early blooms of marine algaes. In the 1600's, early explorers noted that the native tribes of the St. Lawrence River basin had definite "taboos" toward eating shellfish during certain seasons. However, in New England, and more specifically Massachusetts, red tide was relatively unknown until 1972. During the fall of that year, Hurricane Carrie passed through the Gulf of Maine at a snail's pace during a massive toxic algal bloom in the Bay of Fundy. The counter-clockwise winds intensified the traditional water current patterns and deposited red tide dinoflagellates known as Alexandrium tamarense, along the Maine, New Hampshire and Massachusetts coasts. Thus was ushered in the "modern era" of red tide for the Bay State.

Biological Sketch

Alexandrium is a single-celled dinoflagellate 30 to 40 microns in size. In most cases, reproduction is asexual during optimum conditions. During periods of stress or nutrient deficiencies, reproduction reverts to sexual. Binary cellular fission occurs at the rate of about once a day. During nonvegetative periods, the phytoplankton will encapsulate into a cyst stage that settles into the benthic substrate where it can comfortably overwinter or remain dormant for several years before becoming resuspended and ready for germination. Normally, even blooms large enough to cause toxicity problems do not exhibit the "red" coloration. However, during the early seventies in Massachusetts, at least one massive bloom was indeed observed as "red tide". Large blooms have also been known to be luminescent. Nutrients include nitrogen, phosphorous and fresh water while limiting factors, other than nutrients and favorable media, include zooplanktonic grazing, algaecides and less than optimal water temperatures. Motility is accomplished by a flagellum with vertical migration to the pycnocline during the night or periods of nutrient deficiencies in the upper strata of the water column.      

Current Monitoring and Response Program

The Division of Marine Fisheries initiates its annual coastline-wide toxin monitoring program in early April and continues on a weekly basis until November. These dates have been the traditional limits due to the general seasonality of Alexandrium, but may be extended if toxin remains at significant levels beyond the projected end-date.


The annual initiation of sampling is dependent upon several factors: elevated toxin results from the state of Maine, and/or the historical seasonality of Alexandrium planktonic blooms. The Maine results are used due to the coriolis effect causing a north-to-south infusion of the toxic dinoflagellates being carried by overlying freshwater lenses from their large rivers.

Shellfish samples, predominantly the blue mussel, Mytilus edulis, are collected on a weekly basis from 16 primary stations (4 north shore and 12 south shore). Mussels are used as the shellfish of choice because they're considered the best sentinel species for the PSP toxin, i.e., they have the capacity to uptake and release toxins of ambient dinoflagellates in close temporal relationship to the actual duration of Alexandrium blooms. Other species, e.g., the surf clam Spisula solidissima are collected at selected locations and usually on a secondary basis. These animals, unlike Mytilus, have a tendency to retain toxins in tissue well beyond the initial effects of the passing bloom thus eliminating them as effective temporal indicators and causing the closures on their being fished to be extended far beyond other species.

If significant elevations of toxins are noted in primary site samples, more are then collected immediately from the original sites exhibiting abnormal levels and from peripheral secondary sites. At these secondary sites (total of 47 throughout the Commonwealth), different species are collected to monitor the toxin uptake and release differences and to effectively control the fishing for these species during an event.     

Response To Elevated Toxin Levels

As biotoxin levels rise above 50ug/100g of shellfish tissue, sampling is conducted more frequently at affected primary sites and extended into selected secondary sites. When levels equal or exceed 80ug/100g, the area is closed (see HARVESTING CONTROL... below) and sampling continues until 3 consecutive samples result in levels of less than 80ug. In many instances one or more species may exhibit significant reductions in toxins while others in the same growing area retain unacceptable levels. Sampling and closures reflect these levels and will be maintained until such time as the restricted species is toxin free. Therefor, the harvesting of one species may be allowed in an area while that of another is not.

Harvesting Controls During Toxic Events

As noted above, 80ug is the trigger point at which areas are "officially" reclassified to PROHIBITED and notices of closures are generated and mailed. Immediately upon notification by the lab of elevated levels, phone calls are made to the shellfish constables and/or other officials of towns effected. A computerized E-mail notice is sent to state personnel responsible for monitoring PSP events throughout the state and to the Environmental Police. Written notices containing exact area descriptions and the species effected are composed and mailed immediately following the phone and E-mail communications. Every week following the first event, an E-mail informational notice is continued to select state agencies informing them of the ongoing status of the toxin events.

When toxin levels fall below 80ug for three consecutive samples, written notices reclassifying the effected areas are prepared and mailed. Phone communications are also made to the towns to ensure a rapid re-opening of shellfish growing areas:   

Other Monitoring Technologies

Other indicators of possible toxic events or the portent thereof are also used. During the past two years, the Division has been working closely with scientists from Woods Hole Oceanographic Institute. If results of their water sampling research indicated elevated numbers of cells (dinoflagellates) proximal to shellfish growing areas or their computerized satellite surveillance indicated extensive freshwater influences that may represent a viable medium for the introduction or in situ growth of Alexandrium, sampling in those areas was considered.

In keeping with this cooperative spirit, anytime the Division's sampling indicated elevated levels in a given area, the Woods Hole team was notified. In response, they collected water samples from the area and examined them to compute actual numbers of Alexandrium. In the future when sufficient concomitant data is available, it may be possible to more closely determine the relationship of biotoxin levels in shellfish and the densities of dinoflagellates in the area.   

PSP Database

As one may imagine, the number of samples and subsequent results collected since 1972 would be relatively extensive--and it is. To date, more than 16,000 recorded results have been compiled and stored in a relational database maintained by the Division. Such diverse information as collection date, species, town, site, bioassay results, etc. make up the record format and represents an array that affords Division personnel and fellow-scientists the opportunity to analyze toxin events over a period of more than 22 years.

Species specific observances, geographical occurrences, monitoring, and other analysis is now possible using the database. Although there is a great reticence to use the current database information predictively, with a broadening of data collection during sampling and further collaboration with other scientists in the field, general forecasting of events may become possible.

Currently, the data is being reviewed to establish a historical perspective of toxin occurrences over the past 22 years. This study will highlight elevated events and their geographic frequencies. Future study considerations may be directed toward a treatise on the economic impact on selected towns and species specific fisheries. Collaborative efforts will possibly merge the Division's PSP database with meteorological and hydrographical data collected over a long period of time by Woods Hole researchers.     

Future Direction

The scope and direction of the Division's biotoxin monitoring program will slightly change during the upcoming season. Plankton sampling stations in the Buzzard's Bay area and possibly on Martha's Vineyard and Nantucket islands may be established to determine possible planktonic blooms in areas not traditionally having toxic shellfish. To determine temporal and spatial extents of biotoxins in deeper fishing areas, we will be continuing the "vessel of opportunity" program where samples will be collected by these vessel in generally assigned locations.
Other biotoxins are also being considered for monitoring, i.e., domoic acid; Amnesic Shellfish Poisoning (ASP), and Diarrhetic Shellfish Poisoning (DSP). Because the causative agent of ASP, the diatom Nitzcshia pungens f. multiseries occurs primarily in the late fall and winter and the dinoflagellate responsible for DSP is peculiar to warmer seas and seasons, the biotoxin monitoring program would have to be extended to year-round and totally state-wide. Unfortunately, budget and manpower constraints negate an extension of the program into these two areas during this years monitoring. Future monitoring, however, may be mandated by the FDA.

As alluded to above, the Division, in conjunction with the Federal Food and Drug Administration, will be instituting a plankton sampling program throughout the state using volunteers from the general community and colleges. This effort will focus on sampling for the PSP species Alexandrium on a regular basis (probably weekly) at sites where shellfish samples are currently being sampled for toxin and at other locations which may experience varying levels of planktonic bloom activity. Each volunteer is trained in the identification of the organism and is issued a Swift field microscope and sampling nets and containers. This information is then coordinated with the overall biotoxin monitoring program in order to maintain a more multi-faceted perspective.

For further information on the Division's monitoring program, contact Mike Hickey