What Are Harmful Algal Blooms (HABs)?

     Harmful algae are microscopic, single-celled plants that live in the sea. Most species of algae or phytoplankton are not harmful and serve as the energy producers at the base of the food web, without which higher life on this planet would not exist.

     Occasionally, the algae grow very fast or "bloom" and accumulate into dense, visible patches near the surface of the water. "Red Tide" is a common name for such a phenomenon where certain phytoplankton species contain reddish pigments and "bloom" such that the water appears to be colored red. The term "red tide" is thus a misnomer because they are not associated with tides; they are usually not harmful; and those species that are harmful may never reach the densities required to discolor the water.

     Unfortunately, a small number of species produce potent neurotoxins that can be transferred through the food web where they affect and even kill the higher forms of life such as zooplankton, shellfish, fish, birds, marine mammals, and even humans that feed either directly or indirectly on them. Scientists now prefer the term, HAB, to refer to bloom phenomenon that contain toxins or that cause negative impacts.

Humans at the Top of the Food Web

     The consumption of shellfish (e.g. mussels, clams) is one the most common ways for algal toxins to reach the highest levels of the food web affecting humans. In the United States, state management programs are responsible for monitoring the concentration of the toxins in shellfish and closing the shellfish beds for harvest if the levels rise above dangerous limits. Marketable shellfish are generally considered to be safe, but in spite of these precautions, there are known illnesses.

     One dramatic example was from 1990, when six fishermen almost died from eating mussels during a fishing trip on Georges Bank, a productive offshore finfish and shellfish area 100 miles east of Cape Cod, MA. After a hard day of fishing, the fishermen settled down in the ship's galley to eat a pot of steamed mussels that they had incidentally caught in their nets. The Captain, who had joined the meal later than the rest of the crew, witnessed his fellow fishermen become incapacitated due to the paralytic effects of the toxin. He himself also became ill, but was capable of sending an urgent radio message to the US Coast Guard. The Coast Guard airlifted the men to the nearest hospital located on Nantucket Island, MA where they were treated using respiratory therapy to sustain their breathing and prevent them from dying due to paralysis of the lungs. Fortunately, all the men recovered and were back fishing within a few weeks. The event, presumably caused by a massive Alexandrium bloom transported offshore from areas along the northeast coast, closed the surf clam industry on Georges Bank to further harvest. Georges Bank is an offshore area too vast to monitor and is outside the states' jurisdiction, so the US government maintains jurisdiction and currently has a ban in place for the harvest of surf clams which are known to retain the toxins for many years.

Human Illness Associated with Harmful Algae

     Man is exposed principally to the naturally-occurring toxins produced by harmful algae through the consumption of contaminated seafood products. The most significant public health problems caused by harmful algae are:

• Amnesic Shellfish Poisoning (ASP)
• Ciguatera Fish Poisoning (CFP)
• Diarrhetic Shellfish Poisoning (DSP)
• Neurotoxic Shellfish Poisoning (NSP)
• Paralytic Shellfish Poisoning (PSP)

Each of these syndromes are caused by different species of toxic algae which occur in various coastal waters of the US and the world. With the increase in interstate and international transport of seafood, as well as international travel by seafood consumers, there are virtually no human populations that are free of risk. Since 1978, illnesses in the US due to natural algal toxins have included PSP, NSP, CFP, and ASP. No incidents of DSP have yet been verified in this country. Although records are incomplete because reporting to the Centers for Disease Control (CDC) is voluntary, evidence indicates that ciguatera was responsible for about half of all seafood intoxications. A growing body of evidence indicates that incidents of ASP are on the increase and that DSP may shortly make its debut in the United States, since the causative organisms occur throughout the temperate coastal waters of the US.

• Amnesic Shellfish Poisoning (ASP)

Causative organisms: Pseudo-nitzschia sp.

Toxin produced: Domoic Acid

• ASP can be a life-threatening syndrome. It is characterized by both gastrointestinal and neurological disorders (Bates et al., 1989). Gastroenteritis usually develops within 24 hours of the consumption of toxic shellfish; symptoms include nausea, vomiting, abdominal cramps, and diarrhea. In severe cases, neurological symptoms also appear, usually within 48 hours of toxic shellfish consumption. These symptoms include dizziness, headache, seizures, disorientation, short-term memory loss, respiratory difficulty, and coma. In 1987, four victims died after consuming toxic mussels from Prince Edward Island, Canada. Since that time, Canadian authorities have monitored both the water column for the presence of the causative diatom, and shellfish for the presence of the toxin, domoic acid. Shellfish beds are closed to harvesting when the domoic acid concentration reaches 20 µg/g shellfish meat. Fish and crab viscera can also contain domoic acid, so the risk to human consumers and animals in the marine food chain is more significant than previously believed.

Ciguatera Fish Poisoning (CFP)

Causative organisms: Gambierdiscus toxicus, Prorocentrum spp., Ostreopsis spp., Coolia monotis, Thecadinium sp. and Amphidinium carterae

Toxins produced: Ciguatoxin/Maitotoxin

• CFP produces gastrointestinal, neurological, and cardiovascular symptoms. Generally, diarrhea, vomiting, and abdominal pain occur initially, followed by neurological dysfunction including reversal of temperature sensation, muscular aches, dizziness, anxiety, sweating, and a numbness and tingling of the mouth and digits.  Paralysis and death have been documented, but symptoms are usually less severe although debilitating (Miller, 1991). Recovery time is variable, and may take weeks, months, or years. Rapid treatment (within 24 hours) with manitol is reported to relieve some symptoms. There is no antidote, supportive therapy is the rule, and survivors recover. Absolute prevention of intoxication depends upon complete abstinence from eating any tropical reef fish, since there is currently no easy way to measure routinely ciguatoxin or maitotoxin in any seafood product prior to consumption.

Diarrhetic Shellfish Poisoning (DSP)

Causative organisms: Dinophysis sp.

Toxin produced: Okadaic Acid

• DSP produces gastrointestinal symptoms, usually beginning within 30 minutes to a few hours after consumption of toxic shellfish (Yasumoto and Murato, 1990). The illness, which is not fatal, is characterized by incapacitating diarrhea, nausea, vomiting, abdominal cramps, and chills. Recovery occurs within three days, with or without medical treatment.

Neurotoxic Shellfish Poisoning (NSP)

Causative organism: Gymnodinium breve

Toxins produced: Brevetoxins

• NSP produces an intoxication syndrome nearly identical to that of ciguatera. In this case, gastrointestinal and neurological symptoms predominate. In addition, formation of toxic aerosols by wave action can produce respiratory asthma-like symptoms. No deaths have been reported and the syndrome is less severe than ciguatera, but nevertheless debilitating. Unlike ciguatera, recovery is generally complete in a few days. Monitoring programs (based on G breve cell counts) generally suffice for preventing human intoxication, except when officials are caught off-guard in previously unaffected areas.

Paralytic Shellfish Poisoning (PSP)

Causative organisms: Alexandrium spp.,Gymnodinium catenatum, Pyrodinium bahamense

Toxins produced: Saxitoxins

• PSP, like ASP, is a life threatening syndrome. Symptoms are purely neurological and their onset is rapid. Duration of effects is a few days in non-lethal cases. Symptoms include tingling, numbness, and burning of the perioral region, ataxia, giddiness, drowsiness, fever, rash, and staggering. The most severe cases result in respiratory arrest within 24 hours of consumption of the toxic shellfish. If the patient is not breathing or if a pulse is not detected, artificial respiration and CPR may be needed as first aid. There is no antidote, supportive therapy is the rule and survivors recover fully. PSP is prevented by large-scale proactive monitoring programs (assessing toxin levels in mussels, oysters, scallops, clams) and rapid closures to harvest of suspect or demonstrated toxic areas.

Student Activities

1. Find out if there have been any harmful algal blooms in waters near you in the last few years.  What kind of organism was involved? Was it dangerous to other marine life, or to humans? What was believed to be the cause of the bloom?

2. Pfiesteria is an algal bloom that has been featured in the news in recent years.  Investigate whether it poses a serious health threat to humans, and under what conditions it is believed to thrive.

3. Ask students if they or anyone they know has ever gotten sick from something related to the ocean. Ask the students what illnesses humans or other organisms can contract from the ocean.

Assign students to groups. Each group is responsible for researching an illness on the above list.  Presentations on their assigned illness will be made to the class. The presentation must include:

• Description of organism responsible for the illness, including a picture or other visual aid
• Locations of recent outbreaks
• How humans contract the illness
• Symptoms of illness
• Length of beach/fishing closure, if applicable
• Treatment, if available
• Severity / Potential mortality rate
• Preventative steps, or ways to reduce the outbreak
• Does the illness occur in isolation or in conjunction with other HABs
• Description of organisms other than humans that are affected by the HAB

Assessment for this activity:  Groups are assigned an illness, and they act out the symptoms related to the ailment, and the other students are responsible for diagnosing them, based on what they learned from each other’s presentations.

 Assessment

1. Discuss how the following types of pollution affect marine life: nutrients, pathogens, and plastics.

2. What are Harmful Algal Blooms and why do they pose threats to human health? Discuss two types of seafood poisoning, including the type of toxin produced, and several physical symptoms.

3. List three marine organisms (plants or animals) and describe their contributions to human health.

Additional Resources

The Harmful Algae Page

http://www.redtide.whoi.edu/hab/default.html

Sea Grant Focal Points, April, 1998 newsletter

http://www.epa.gov/owow/estuaries/coastlines/summer98/harmfulalga.html

Bigelow Laboratory -- Toxic and Harmful Algal Blooms

http://www.bigelow.org/hab/

Links to many more HAB sites

http://www.coexploration.org/habs/html/resources.html

Blue Flag Beaches

http://www.blueflag.org/

Pfiesteria

http://www.boatus.com/cleanwater/outreach/pfiesteria.htm

Oceans and Human Health Links

Ocean PharmaSea

http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/sea_store_PharmaSEA.html

Article from Bermuda Biological Station for Research, How the Health of Our Oceans Affects Our Well-being

http://www.bbsr.edu/Ocean_Human_Health/currents/currents.html

Workshop on Indicators of Ocean and Human Health (Bermuda Biological Station for Research)

http://www.bbsr.edu/Ocean_Human_Health/workshop/workshop.html

National Sea Grant Office article on Marine Environmental Health Linkages to Human Health

http://www.seagrantnews.org/news/19990120cpbrief_health/