Yesterday's Island Today's Nantucket
Volume 38 Issue 11 • July 10 - 16, 2008
now in our 38th season

Red Tide Rising

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

Our surrounding salt water and the water in our ponds are full of microscopic algae and bacteria that form the basis of the food web. Sometimes due to a combination of factors, the algae species can “bloom” or increase rapidly in numbers, tinting the water and causing adverse impacts.  The phenomenon is not that different from the way cancer cells multiply in tissue: something triggers a beneficial growth situation, introducing more food, a change in temperature, or something else metabolically advantageous that causes these organisms to multiply out of control.  The term “red tide” is usually used by lay people to refer to any number of large explosions of algae populations. Oceanographers and marine biologists use the term “harmful algal blooms” (HABs) to refer to large outbreaks of algae that release toxins that can be concentrated in creatures which ingest algae, or can cause fish kills and other adverse effects. When people use the term “red tide,” they sometimes are referring erroneously to blooms that discolor the water but cause no harm (such as the swirls of red macro-algae off of Codfish Park).  And sometimes, an HAB is made of blooms of highly toxic cells that cause problems at very low cell concentrations with no obvious color that can be seen with the naked eye.  A fluorometer, which measures the natural emission of electromagnetic radiation, or fluorescence, given off by phytoplankton is used to detect these “clear” blooms.

According to the Center for Disease Control, the term red tide is used specifically when referring to the marine algae called Karenia brevis (K. brevis) which, when it grows quickly, creates blooms that can make the ocean appear red or brown.  K. brevis produces powerful toxins called brevetoxins, which have killed millions of fish and other marine organisms.  Red tides have damaged the fishing industry, shoreline quality, and local economies in states such as Texas and Florida.  Because K. brevis blooms move based on winds and tides, pinpointing a red tide at any given moment is difficult. 

In addition to killing fish, brevetoxins can become concentrated in the tissues of shellfish that feed on K. brevis.  People who eat these shellfish may suffer from neurotoxic shellfish poisoning (NSP), a food poisoning that can cause severe gastrointestinal and neurologic symptoms, such as tingling fingers or toes.  In addition, this algae and several others that form HABs release a stinging spray into the air that causes respiratory distress, burning eyes, and asthma-like constrictions for people near the seashore when the algae blooms under certain weather conditions (onshore wind, or low wind). If you never want to swim again, go to and click on species to read about the many types of organisms which cause a wide range of damage to the ecosystem, and occasionally, to humans.

In ancient historical Egyptian texts and in the Bible (Exodus, one of the 10 plagues), the story "and all the waters were turned to blood, and the fish died, and the water stank" was probably testament to early blooms of marine algae. In the 1600s, early explorers noted that the native tribes of the St. Lawrence River basin had definite taboos against eating shellfish during certain seasons which was likely a protection against consuming shellfish when these toxins may be in the water.  This same reasoning lies underneath the Cajun tradition closely followed in New Orleans of not eating oysters in any month that does not have an “r in it (May-August). 

In New England, and more specifically Massachusetts, red tide was relatively unknown until 1972.  According to the Massachusetts Division of Marine Fisheries (Mass-DMF), during the fall of 1972, Hurricane Carrie slowly passed through the Gulf of Maine 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 fundyense/ tamarense, along the Maine, New Hampshire and Massachusetts coasts.  This was the beginning of the red tide menace in the Bay State.  There is quite a bit of healthy genetic debate and discussion in the scientific literature about whether the primary species responsible for HAB blooms in New England is Alexandrium tamarense or Alexandrium fundyense, so for the rest of this article, we’ll stick with the term Alexandrium. Both species are very similar in appearance and certainly in action and are indistinguishable even when using RNA gene sequence data which indicates some cross variant between the species (called the “tamarensis” complex) may be occurring.  NOAA and Woods Hole Oceanographic Institute scientists tend to use the term Alexandrium fundyense, which was identified early on as the more toxic of the two species and the more common in the Gulf of Maine, where “red tides” in New England are born.

Our culprit, Alexandrium, exhibits similar dangerous toxin effects to other HAB species, but its spread is fortunately often restricted to smaller areas due to New England’s cold water temperatures and enclosed bays.  Alexandrium is a single-celled dinoflagellate 30 to 40 microns in size, or just half the size of the diameter of a human hair.  It looks somewhat like a soccer ball with a tail. A dinoflagellate is a protozoans with two flagellums, which are whip-like appendages for locomotion (from the Greek dīnos, whirling + Latin flagellum, diminutive of flagrum, or whip). Few people know that many phytoplankton species actually are very mobile and will move up and down in the water column to “chase” nutrients and even avoid excess sunlight.

Scientist believe that the cause for some of our recent outbreaks of “red tides” are large storms in the spring which wash excess nutrients such as fertilizers (containing phosphate and nitrate) and fresh water into our coastal waters.  This sheet flow effect has been exacerbated by land use changes from farming to paving to the reduction and drainage of our protective salt marshes.  These nutrients feed the relatively small populations of algae, which then begin to grow faster (going from sexual reproduction to asexual reproduction, no time for romance!). During nonvegetative (no-growth) periods, the phytoplankton will encapsulate into a cyst stage that settles into the benthic substrate (bottom mud) 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.

Alexandrium toxin (saxitoxin) causes paralytic shellfish poisoning (PSP) as opposed to some of the other biotoxins released by other organisms which cause Amnesic Shellfish Poisoning (ASP), and Diarrhetic Shellfish Poisoning (DSP).  Now the reference to plagues seems a little too fitting.  Saxitoxin attacks the human nervous system within 30 minutes with symptoms that may include numbness of the lips, tingling of the extremities, uncoordinated movements, incoherent speech, and nausea.  PSP symptoms may be mistaken for drunkenness.  In severe (and very rare) cases, paralysis of the breathing mechanism can cause death within a few hours.  From the 1950s until President Nixon ended the program in 1969, the CIA experimented with saxitoxins which can be 1000 times more lethal than Sarin gas.

No cases of death attributed to PSP have been reported in New England, although this syndrome is associated with fatalities elsewhere in the U.S. and the world.  The effects are definitely noticeable in shorebirds which feed on clams and other shellfish which are constantly filter feeding on phytoplankton including Alexandrium.  The birds that have been suspected of PSP poisoning have a staggered, drunken gait and often will die of starvation due to their inability to feed if they don’t die from the toxin. 

The shellfish accumulates the toxins in their tissues although they are typically not harmed by the toxins, then an unsuspecting bird or person who ingests the entire shellfish can become exposed to the toxin. The toxin is stored in the gut, gonads, and other soft tissues of shellfish, not the muscle, which is why it is all right to eat some species such as scallops in which we are only eating the adductor muscle.  The ability of blue mussels (Mytilus edulis) to quickly take up and release the toxins makes them a perfect indicator species; in other words, the concentrations of Alexandrium in a blue mussel will correspond directly to the concentration of the bloom organisms in the water.  The Marine Department (and similar officials through the state and region) sends these mussels in weekly or even twice a week to be tested in state lab facilities and the results are available very quickly, making it possible to detect whether a bloom has spread. The state also tests 16 primary sites of concern and up to 47 secondary sites on the north and south shore. As biotoxin levels rise above 50ug/100mg of shellfish tissue, sampling is conducted more frequently at affected primary sites and extended into selected secondary sites.  When levels equal or exceed 80ug/100mg, an area is closed and sampling continues until 3 consecutive samples result in levels of less than 80ug.

According to Mass-DMF, as of July 4th, the southern and eastern waters off Nantucket are closed to fishing for ocean quahogs, whole sea scallops, moon snails, and surf clams.  Finfish, lobsters, shrimp, and crabs are safe to eat even when they are caught in red tide waters.  Tests have not indicated that a closure is needed yet for the Nantucket Sound or for Nantucket Harbor although bacterial related closures are still in effect.  The Mass-DMF’s web page on HABs documents the testing done in Massachusetts ( and the Woods Hole Oceanographic Institute has a national and international program dedicated to research on HAB’s that has collected over thirty years of research.

Unfortunately, in addition to birds and humans, marine mammals can be harmed by HAB and scientists reported that in 1987, the deaths of 14 humpback whales off Massachusetts in Cape Cod Bay were traced to the whales eating mackerel, which in turn had eaten smaller fish and zooplankton, which had consumed large amounts of Alexandrium.  In 2005, Massachusetts had the largest Alexandrium bloom observed since 2005, with many areas closed that had never recorded closures before. A combination of two unusually late Nor'easters following heavy spring rains caused this large outbreak.  In Massachusetts alone, direct economic impacts to the shellfish industry were estimated at $18 million. Although not quite as severe as the influx we had in 2005, a “red tide” is rising around Nantucket in 2008.  These organisms exist naturally in our oceans and bottom sediments and some blooms will occur regardless of our actions, but better management of land surrounding freshwater rivers and estuaries that spill into our harbors and bays and less use of fertilizers can help alleviate these problems and protect our fishing industry.

Good News: As of Monday, July 7 and just before we went to press, fishing grounds on the North Shore and in Chatham and Orleans were reopened as the red tide was dispersed by warmer waters.  Hopefully this means that the red tide of 2008 will not be as devastating as the 2005 season.

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