Harmful Algal Blooms

Dinoflagellate Blooms, “Red Tides” “Rusty Tides, PSP, and Harmful Algal Blooms

Related Pages:   Beach Information  |   Nuisance Algae  |   Seafood Safety


Excessive growth of microalgae in coastal waters may result in adverse impacts to the ecosystem of human health, and are often broadly defined as harmful algal blooms (HAB). “Red Tides” are a long used lay term referring to blooms of the dinoflagellate algae Alexandrium fundyense (a type of microscopic phytoplankton). An algal “bloom” is a population explosion of microalgae where cell densities may exceed millions of cells per liter of water, and can even result in the discoloration of the water. However, Alexandrium blooms may not occur at high enough concentrations to discolor the water red, yet still have adverse effects. This algae can contaminate filter-feeding shellfish with a toxin that results in a syndrome known as paralytic shellfish poisoning (PSP) when the shellfish are consumed. Shellfish are monitored by the Massachusetts Division of Marine Fisheries for this PSP toxin contamination. When the PSP toxin is elevated in mussels (the indicator species used by DMF), they will enact a PSP shellfish bed closure in a region. The press typically report these as “red tide” closures. Since 2009, there have been no shellfish bed PSP closures in Buzzards Bay, however, in most years, other areas of Massachusetts have had PSP closures, particularly in waters north of Cape Cod. Go to the DMF PSP website for the latest information. You should always consult with your local shellfish constable for the status of shellfish bed closures your community.

Since 2005, the Buzzards Bay Coalition received reports of “Rusty Tides” caused by the non-toxic dinoflagellate Cochlodinium polykrikoides. Go to the bottom of this page to learn more about that species of microalgae.

The most widespread PSP closures in Massachusetts in recent years occurred during the summers of 2005 and 2006. Coincidentally, because of exceptionally heavy rains in early June of 2006 (6 to 10 inches of rain), on June 7, 2006 the state also closed all of state waters to shellfishing, including Buzzards Bay. This occurred in addition to the PSP closures. The first closure of any part of Buzzards Bay due to PSP occurred in 2005, when the northernmost end of the bay was closed, near the canal. That year, large portions of the rest of state suffered from prolonged PSP closures that had a disastrous impact to the incomes of commercial shellfishermen, and the state even sought federal disaster relief funds.

On October 7, 2016, Buzzards Bay was closed to shellfishing for the first time due to a bloom of the diatom Pseudo-nitzschia. The Massachusetts Division of Marine Fisheries (DMF) has banned the harvesting of shellfish in all of Buzzards Bay, Mount Hope Bay and Lackeys Bay off Naushon Island on Vineyard Sound. The ban later extended to Nantucket Sound. Certain Pseudo-nitzschia species can produce a toxin called domoic acid. This biotoxin can concentrate in filter feeding shellfish. High concentrations of domoic acid in shellfish can cause Amnesic Shellfish Poisoning (ASP) with symptoms that include vomiting, cramps, diarrhea and incapacitating headaches followed by confusion, disorientation, permanent loss of short-term memory, and in severe cases, seizures and coma.

map of maximum of the 2005 PSP closures in Massachusetts
This map (pdf file) shows the maximum extent of the 2005 PSP closures.

Information about the Massachusetts 2005 Red Tide and PSP closures in Buzzards Bay

Beginning on April 27, 2005 the Massachusetts Division of Marine Fisheries initiated a prohibition on the taking of shellfish in Nauset Harbor, in Orleans because of elevated levels of paralytic shellfish poison (PSP) toxin in shellfish. A wider scale closure was initiated at Cape Ann to New Hampshire on May 19. This closure expanded southward, until on May 27, the Division of Marine Fisheries announced a widespread prohibition on the taking of shellfish in Massachusetts Bay, Cape Cod Bay, and upper Buzzards Bay. On the outer Cape, the closure continued to extend south to Monomoy Island on June 2, and further south to Nantucket Island on June 3. By June 6, the PSP closure extended southwest to Edgartown on Martha’s Vineyard.

On June 9, 2005, Governor Mitt Romney declared an economic disaster in Massachusetts, allowing the state to seek federal disaster aid. On June 10, DMF closed Federal Waters adjacent to Massachusetts to the taking and landing of shellfish (read the DMF notice). On June 16, closures extended to the entire south coast of Martha’s Vineyard closed. In response to the Governor’s declaration, the Small Business Administration announced it would issue low-interest loans to qualified individuals on June 21. However, on June 24, the federal government decided the Red Tide outbreak and resulting PSP shellfish bed closures did not qualify for federal disaster relief.

<i>Alexandrium fundyense</i>
Alexandrium fundyense.

PSP closures are enacted in response to a bloom of a type of a type of planktonic algae, a dinoflagellate of the genus Alexandrium. Blooms of Alexandrium are often called “Red Tide” because the water can have a pinkish tinge from the density of algae in the water, although it is possible to have PSP closures without any discoloration of the water, so Red Tide has become synonymous elevated Alexandrium populations in the water that result in PSP shellfish closures. PSP contamination of shellfish is a threat to human health because the algae produce PSP toxins, specifically one called saxitoxin, that can accumulate in shellfish during blooms. PSP toxin is a threat to human health, and can even cause death.

While PSP closures occur more regularly in the cold waters north of Cape Cod, in 2005 for the first time ever, the PSP closure extended through the Cape Cod Canal and south into Buzzards Bay to Wings Neck in Bourne and Stony Point Dike in Wareham. This area includes Buttermilk Bay, Onset Bay, and Phinneys Harbor. The inclusion of the north end of Buzzards Bay reflects the historically high levels of PSP toxin observed at the end of May in Cape Cod Bay, that were transported southward, through the canal. The exceptionally high levels of Alexandrium in Cape Cod Bay were believed to be the result of heavy spring rains and unusual May Nor’easters that drove in the offshore phytoplankton bloom.

Click to read the May 27, 2005 New Hampshire to Buzzards Bay PSP closure notice.

On July 1, 2005, DMF reopened the closed areas of Buzzards Bay and few selected areas of Cape Cod. Openings continued gradually through July and August, but a few areas remained closed as shown in the map above. Concerns remain about the possible long-term implications of future outbreaks of Red Tide south of Cape Cod, and in Buzzards Bay, and whether the dinoflagellate cysts that remain in the bottom sediments from this outbreak, will make these areas more prone to future Red Tides and likely PSP closures. It is presumed that cysts deposited in one season provided the inoculums for new outbreaks in future years. Some studies have shown that Alexandrium cysts may survive in sediments under natural conditions for at least several years.

Newspaper and Magazine Articles, and information pages

Woods Hole Oceanographic Institution Northeast PSP page
2008 WHOI Oceanus Magazine Article on Red Tide
June 15, 2005 New Bedford Standard Times article: Red tide closes shellfish areas
May 22, 2008 New Bedford Standard Times article: Red Tide future uncertain
May 24, 2008 New Bedford Standard Times article: Red Tide closes part of Cape Cod
June 24, 2005 Boston Globe article: US denies disaster aid for red tide in Massachusetts
Massachusetts DMF PSP Biology Page.
Massachusetts Department of Public Health Page on Red Tide poisoning.
WGBH:Rust Tide in Buzzards Bay: More Questions Than Answers.
Woods Hole Oceanographic Institution Harmful Algal Bloom page
NOAA New England Red Tide Information.


Cochlodinium Blooms in Buzzards Bay (Rusty Tides)

Cochlodinium bloom as observed in Buzzards Bay
A boater’s view of the “rust colored” water observed off North Falmouth in September 2005 caused by Cochlodinium. Photo taken by Larry Soule, Baywatcher for the Buzzards Bay Coalition.

In September 2005, we received the first report of a Cochlodinium Bloom in Buzzards Bay, sometimes referred to as “Rusty Tide”, to distinguish it from the PSP related “Red Tides.” Cochlodinium blooms may have occurred previously in Buzzards Bay, but if so, they were not widely reported. We have received reports of these Rusty or Rust Tides in every subsequent year. For example, in August 2012, Cochlodinium blooms were widely reported in the northern half of Buzzards Bay, both in bays and offhsore, in late August. We also received a report from the south central portion of the bay from Dartmouth Health Agent Wendy Henderson who observed a Cochlodinium Bloom at Anthony Beach near Clarks Cove, exposed coast areas near Round Hill and Salters Point.

The species of dinoflagellate is Cochlodinium polykrikoides (synonym= C. heterolobatum). The 2005 bloom in Buzzards Bay had counts that exceeded 7.6 million cells per liter, and Rusty patches of water were observed primarily off Falmouth and Bourne as illustrated by the photograph to the right. The 2005 bloom subsided a few weeks later after waters cooled.

Unlike the Alexandrium dinoflagellate, Cochlodinium does not contain neurotoxins that affect people, but like Alexandrium, it contains reddish pigments, so that in large enough concentrations, Cochlodinium can also discolor coastal waters with a rusty hue if it appears in great enough concentration. Cochlodinium had been considered a Harmful Algal Bloom (HAB) species simply because in high concentrations in contained systems, it caused the death of fish by consuming all the oxygen in the water (plants generally produce excess oxygen in the day, but like animals, they are always consuming oxygen too). However, more recent studies have concluded that Cochlodinium polykrikoides in fact exhibit a pronounced chemical toxicity (Gobler et. al, 2008; Harmful Algae 7(3):293-307). Tanga and Gobler (2008, Harmful Algae, 8(3):454-462) documented that juvenile bay scallops experienced “100% mortality during 3 days exposure to cultures at cell densities an order of magnitude lower than raw bloom water.” These authors proposed that the algae releases reactive oxygen compounds as the mechanism of mortality, but a subsequent study by Kim et. al (2009; Biosci Biotechnol Biochem. 73(3):613-8.) suggested that other compounds might be the cause of observed mortality, which cause the observed neurotoxic, hemolytic, and hemagglutinative effects. Large concentrations of Cochlodinium may also affect the growth, survival, and development of some zooplankton larvae of more desirable species, like oysters.

Microscopic view of
Cochlodinium spp.
<i>Cochlodinium</i> dinoflagellate

Warm waters and high nutrients are thought to contribute to blooms of Cochlodinium. In Peconic Bay on Long Island, fertilizer runoff and surface and groundwater discharges of wastewater is believed to have contributed to some recent “Brown Tides” and Cochlodinium blooms observed in that estuary in 2004 and 2005. The Peconic Bay National Estuary Program has prepared and easy-to-understand Cochlodinium Page and Fact Sheet that contains much useful information about the species.

What are Dinoflagellates?

Dinoflagellates are a broad group of single celled organisms generally classified as a Class (Dinoflagellata) in the phylum Protista. Protists are a catchall group that includes plant-like organisms and animal-like organisms. Dinoflagellates are typically found floating in the water, and are thus known as plankton. Some dinoflagellates have chlorophyll (and make their own food), and are thus considered “algae” or phytoplankton. Other dinoflagellates eat small plants or animals, and are therefore considered zooplankton. Some dinoflagellates are mixotrophic; that is they both have chlorophyll, and they eat other organisms. Cochlodinium is mixotrophic.

Some dinoflagellates are even parasitic on other animals

The distinguishing features of dinoflagellates that separate them from other Protists include the fact that they have armored plates made of cellulose, they may contain chlorophylls a and c and fucoxanthin (along with other pigments that give them a reddish color), and they have two flagella for swimming through the water, one of which is contained in a spiral groove on the body.

Besides the notoriety of the Red Tide dinoflagellates, many beach goers are familiar with another dinoflagellate know as “sea sparkles.” These are in fact a large (at least for a single-cell organism – 1mm) plankton-eating species of dinoflagellate called Noctiluca that can be seen scintillating in the water as bright sparkles of light at night. [Ctenophore jellies are also bioluminescent, and also cause flashes during nighttime swimming in Buzzards Bay, but they are another story.].

Brown Tides

In recent years, brown tides have been frequently reported in a broad region from Rhode Island to New Jersey, with many occurrences in Long Island embayments, The term “brown tide” is somewhat generic, and can refer to several different phytoplankton species that color the water brown at high concentrations. In Long Island waters, the most common species is Aureococcus anophagefferens. This species is not a dinoflagellate, but is in a diverse class of single celled and multicelled yellow-green and brown algae that includes kelps and diatoms. Unlike Alexandrium spp., as described above, this organism produces a non-toxic bloom and is harmless to humans.