The Red Tide

The red tide occurs when the algae from algal blooms becomes so numerous that it discolors the water. It is also sometime referred to as a Harmful Algal Bloom or “HAB”. This is where the name “red tide”comes from. Some key factors involved in red tides forming are warm ocean surface temperatures, low salinity, high nutrient content, calm seas, and rain followed by sunny days during the summer months. Some effects of the red tide are that it could deplete the oxygen in the water and/or release toxins into the water. The toxins in the water could have negative effects on the health of humans and animals exposed to them. There are three types of algae that can release these harmful toxins, they are Alexandrium fundyense, Alexandrium catenella and Karenia brevis.

This is a great video that helps explain more about red tides and the effects that they can have.


Negative Effects of the Red Tide

The red tide can have negative effects on a wide variety of marine animals. Fish are very commonly affected by the toxins that the algae produces. This is very bad because once some fish are poisoned by the toxins, they can then work their way up the food chain to larger marine animals or even birds that eat the fish. Even whales can be poisoned by the harmful toxins produced by these algal blooms.

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The Red Sea” by St Stev under Flickr

Harmful algal blooms can also be a threat to human health. This most commonly occurs when humans eat shellfish that have been exposed to the toxins. Paralytic Shellfish Poisoning is typically found along the Pacific and Atlantic coasts of the United States and Canada. It can cause paralysis and in extreme cases death. Some of the toxins that cause Paralytic Shellfish Poisoning can be 1,000 times more potent than cyanide.

Diarrhetic Shellfish Poisoning is another example of a harmful effect from eating contaminated shellfish. It is caused by Okadaic acid, which is produced by several species of dinoflagellates, and is usually non deadly to humans. Small amounts of the Okadaic acid usually do not have any harmful effects and only become an issue when large amounts are consumed.

Amnesic Shellfish Poisoning is the third common poisoning that humans will get from eating contaminated shellfish. It can be life threatening and cause both gastrointestinal and neurological disorders.The disorders are caused by the domoic acid. After an incident in Canada in 1987 where 4 people died from Amnesic Shellfish Poisoning, the levels of domoic acid in shellfish are now being monitored.

Positive Effects of the Red Tide

Although some Algal Blooms can be negative towards the environment, this is not always the case. It is actually only a small percentage of Algal Blooms that are harmful. Most are actually beneficial to the environment. This is because they do not produce the harmful toxins, and instead they provide a major source of food and energy to the marine world.

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Toxic Algae Bloom in Lake Erie” by NASA Earth Observatory under  public domain

Effect On Corals

Algal Blooms can have serious effects on corals. Red algae, brown algae, and green algae are a few examples of macroalgae that can have a very negative effect on corals. They do this by outcompeting, overgrowing and eventually replacing sea-grasses and coral reef habitats. According to some research that is being done, harmful tropical algal blooms are increasing in frequency and intensity. This can have a significant impact on coral reefs.

Notable Red Tides

  • 1844: First recorded case off the Florida Gulf Coast.
  • 1972: Red tides killed 3 children and hospitalized 20 adults in Papua New Guinea.
  • 2005: The Canadian red tide was discovered to have come further south than it has in years prior by the ship (R/V) Oceanus, closing shellfish beds in Maine and Massachusetts. Authorities were also alerted as far south as Montauk to check their beds. The experts who discovered the reproductive cysts in the seabed warned of a possible spread to Long Island in the future. This halted the area’s fishing and shellfish industry.
  • 2013: In  January, a red tide occurred on the West Coast Sea of Sabah in the Malaysian Borneo. There were two fatalities reported after they consumed a shellfish that had been contaminated with the red tide toxin.
  • 2015: In September, a red tide bloom occurred in the Gulf of Mexico, affecting Padre Island National Seashore along North Padre Island and South Padre Island in Texas.

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Map of Padre Island National Seashore” by U.S. National Park Service under  public domain

What is Being Done

Scientists have been able to help control the spread of the effects of harmful algal blooms by developing new technology to help track them better. Tracking these harmful algal blooms could help prevent people from eating contaminated shellfish and knowing which areas will be most effected by them. Some examples of the technology that can help with monitoring them is better and more advanced satellite imagery. Also the development of an antidote to the toxins produced is another way to reduce the harmful effects.


8 thoughts on “The Red Tide

  1. Wow, I love this post! I did not know much about red tide prior to reading this and I tried talked about it in my most recent post “Bioluminescence as a Biological Phenomenon in the Ocean”. Maybe I’ll make some edits to my post now that I know more. I find it most scary that it can kill people indrectly by traveling through the food chain to shellfish!

    Liked by 1 person

  2. I did not realize the detrimental effects the Red tide can have on not only organisms living in but also humans that consuming the shellfish. Is it more likely to get poisoned by eating the shellfish raw or cooked? Or is there any difference between the two and if the shellfish is contaminated you get sick either way. I know you stated that the increase of algal blooms is what causes the discolored water, but what makes the algal blooms increase in the first place? Great post and very informative.

    Liked by 1 person

    1. Thank you! And to answer some of your questions, a person definitely has a higher chance of getting sick from eating raw shellfish but there is still a high risk even when it is cooked. Also warm surface temperature, high nutrient content and calm seas are a few of the factors that increase the algal blooms.


  3. I think this post is very cool! Who would of guessed that this phenomenon can be both positive and negative. It amazes me that there are different sickness that one can get by eating shellfish that come in contact with the red tide. Do you know if more areas are affected by others, and if so why?


  4. Alana, this was an interesting post! I had heard about the red tide before but never actually realized what it was and the harmful affects. Here is another great example of how red tides can harm the marine life and such, and even harm us in the food we eat! We need to be careful of that when eating seafood as well as other diseases that could be lurking.


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