Red Tide

A Deadly HAB


Red tide is caused by an outbreak in phtyoplankton, specifically dinoflagellates, due to an increase in nutrients and temperature in the water. The mass of algae expands and feeds off the excess nutrients in the water, created by pollution and chemical run off, and turns the water a deep red color. An example of pollution comes from fertilizer on farms. The fertilizer that farmers put on their crops gets washed away when it rains and runs into rivers and streams. The rivers carry the chemicals to the ocean, where it stays and eventually cause a red tide.

- (NOAA) (Beachapedia) (Gale Science in Context)
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Eutrophication." Tutor Vista. NCS Pearson, 2016. Web. 2 Feb. 2016.

Who's Involved?

Red tide involves dinoflagelletes, or uni cellular phytoplankton. There are three types of dinoflagellates that cause red tide:

  • Alexandrium fundyense- Occurs in the Atlantic, along the coast of the Canadian Maritimes and Southern New England. Releases paralytic shellfish toxins that can cause harm to humans.
  • Alexandrium catenella- Occurs in the Pacific, along the coast of Southern California to Alaska. Also produces paralytic shellfish toxins, and an increase in fish mortality.
  • Karenia brevis- Occurs in the Gulf of Mexico, the West Coast and along the coast of Florida. More toxic than the other types. Can cause severe respiratory illnesses in humans, mass mortality in marine animals, and neurotoxic shellfish poisoning.

(Gale Science in Context) (Carleton)

Ecological Impacts

Red tide has a big health impact on both humans and marine life. The algae in the red tide can produce toxins that lead to illnesses such as:

  • Paralytic shellfish poisoning- This toxin is absorbed by filter feeders (mussels, oysters, scallops,etc.) and can cause severe nervous system damage to humans when ingested, including paralysis, respiratory failure and even death.
  • Amnesic shellfish poisoning- Also absorbed by filter feeders and when ingested can cause loss of short term memory, irregular heart beat, comatose and possible death.
  • Diarrhetic shellfish poisoning- gastronomical illness, causes vomiting, dizziness and abdominal pain when eaten by humans.

If humans submerge themselves in red tide polluted waters they will suffer from respiratory issues, including lung and nose irritations, and respiratory infections (bronchitis, walking pneumonia, etc. )

In marine life, red tide causes many disruptions in the food chain. When the phytoplankton that cause red tide begin to die off, they decompose at the bottom of the ocean, causing a severe decrease in dissolved oxygen. This can cause hypoxic and anoxic water conditions (water with 2 mg/L of DO or less). Small organisms will become paralyzed and die, while larger organisms will swim away. This causes the food web to be destroyed because the producers and primary consumers have died and therefore the predators have no food source. The predators will travel elsewhere to find food, and wherever they go, cause an increase in consumers. There will be less producers and an increase in consumers, and the balance will be thrown off.

(Gale Science in Context) (NOAA)

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Economic Impacts

Every outbreak of red tide is sure to bring some negative impacts on the economy. These impacts are found at both the local and regional levels and can come from many industries including the following;
  • Commercial Fisheries
  • Public Health (Treatment Costs)
  • Shellfish Industry
  • Aquaculture Industries
  • Recreation and Tourism Industries
  • Research
Loss of investment and money in all of the above industries during a red tide outbreak help to contribute to the "estimated annual HAB cost of $50 million" (Woods Hole Oceanography Institute).


Nationwide, there are two main geographic coastline locations most common for red tide.
  • New England/Maine Gulf
  • Florida/Texas Gulf

New England:
The kind of algal species responsible for red tide in the Maine Gulf is Alexandrium that makes toxins in shellfish. Ride tide off the coast of New England is largely based on wind patterns over the span from May to July and can be predicted with the help of seasonal trend observations (NOAA).

Florida and Texan Gulf: The type of algal species causing red tide in these Southern waters where it can grow and thrive is Karenia Brevis. The severity of this Southern algal bloom can be determined by looking to the tides and currents and the time of year (summer months)


What Can Be Done?

There is a constant effort to produce ideas that could help solve the issues brought with HAB's.

  • Decrease amount of human activity increasing nutrient input and changing hydrology of an area
  • Attempt of restricting transportation of cells or resisting cysts of HAB species to areas with live shellfish that threaten public health
  • Technological advancements to monitor suspected regions most susceptible to HAB's
  • Outreach and public education of Harmful Algal Blooms

-(NOAA) (National Sea Grant College Program) (Department of Commerce)-

Works Consulted by: Olivia Freud & Sophi Oehler


Works Cited

“Donate to Mote.” Mote Marine Laboratory and Aquarium. Mote, 2016. Web. 8 Feb. 2016. <>.

“Eutrophication.” Tutorvista. NCS Pearson, 2016. Web. 2 Feb. 2016. <>.

“Harmful Algae Economic Impacts.” Woods Hole Oceanographic Institution. WHOI, 21 July 2012. Web. 1 Feb. 2016. <>.

“Improved NOAA Forecast for Red Tide in Florida.” National Oceanic and Atmospheric Association. NOAA, 3 Aug. 2015. Web. 1 Feb. 2016. <>.

National Sea Grant College Program, et al. “Prevention, Control and Mitigation of Harmful Algal Blooms: A Research Plan.” Woods Hole Oceanographic Institution. WHOI, Sept. 2001. Web. 9 Feb. 2016. <>.

“Red Tide Off Florida.” Visible Earth. NASA, n.d. Web. 9 Feb. 2016. <>.

“Red Tide Wave.” Wordpress. Wordpress, n.d. Web. 9 Feb. 2016. <>.

“Researchers work to find ways to kill red tide.” Herald-Tribune. Gatehouse Media, 6 Sept. 2005. Web. 1 Feb. 2016. <>.

“Shellfish Harvesting Closure Sign.” Woods Hole Oceanographic Institution. Woods Hole Oceanographic Institution, 10 Aug. 2005. Web. 9 Feb. 2016. <>.

“Unprecedented 2009 New England Red Tide Season.” National Oceanic and Atmospheric Association. NOAA, 2009. Web. 1 Feb. 2016. <>.

“What are the economic impacts of red tides and other harmful algae blooms?” About News. About News, 12 June 2015. Web. 4 Feb. 2016. <>.


"What is red tide?" . 3 September, 2014. 1 February, 2016. Web

Bruckner, Monica. "Red Tide." 1 February, 2016. Web.

"Harmful Algal Blooms." 30 September, 2015. 1 February, 2016. Web.

Freedman, Bill. "Red tide." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmouth Lerner. 5th ed. Farmington Hills, MI: Gale, 2014. Science in Context. Web. 2 Feb. 2016.

Aldridge, Susan, and K. Lee Lerner. "Algal blooms." The Gale Encyclopedia of Science. Ed. K. Lee Lerner and Brenda Wilmoth Lerner. 5th ed. Farmington Hills MI: Gale, 2014. Science in Context. Web. 2 Feb. 2016.

"Red Tide." Environmental Encyclopedia. Gale, 2011. Science in Context. Web. 2 Feb. 2016.

"Red Tide." Smithsonian Ocean 1 February, 2016. Web.

" An Insight Into The Red Tide Phenomenon." 1 February, 2016. Web.

"The destructive effects of improper fertilization." Fertilize 1 February, 2016. Web.