What Is Red Tide? And What Causes It?

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Red tide is a pretty daunting and ominous phenomenon whereby the water changes color and takes on a deep red hue.

This crimson tide may look like a harbinger of doom but it’s actually a natural and not entirely uncommon event.

But that doesn’t mean it’s harmless, as red tides can be seriously harmful and detrimental to humans and marine life.

What Causes Red Tides?

Red tides are also known as harmful algal blooms or “HABs”.

They are caused by a type of algae.

These organisms are commonly found in the water, but their numbers are usually so low that they can’t be seen with the naked eye.

During a red tide, the numbers increase and become so dense that the water appears to change color.

The organisms that cause red tides have been around for a long time, longer than humans in fact, but they are becoming more frequent due to human interaction.

It’s believed that sewage treatment plants and pollution from agriculture flows into the ocean and causes the algae to breed faster, triggering resulting red tide bloom.

However, we don’t know for sure why these events occur. What we do know is that there are several factors at play here, and red tidal blooms will depend on temperature, wind, pollution, and water salinity.

When And Where Do Red Tides Occur?

In the United States, red tides are often seen in the Gulf of Mexico, where an organism known as Karenia brevis (K. brevis) causes “Florida red tides” and has been known to spread as far north as the Carolinas.

They are also seen in the Gulf of Maine, where a species known as Alexandrium fundyense is the culprit.

Florida Red Tides

Florida red tides are some of the most common, best-known, and most studied of all red tide events. They are triggered by Karenia brevis, which produces a toxin that can harm all marine creatures, as well as humans.

These events can last for several days or weeks, but they can also extend to many months. They are found almost exclusively in the Gulf of Mexico but are also seen near North Carolina.

The first red tide was recorded in Florida during the middle of the 19th century and there have been numerous incidents recorded since.

Seafood is checked in the area to make sure it’s not contaminated with the toxins from a red tide event, and you can find more information on when and where they appear by checking the MOTE website.

Gulf of Maine Red Tides

Red tides in the Gulf of Maine are caused by an organism known as alexandrium fundyense. As with Karenia brevis, this organism can cause problems for humans when it contaminates seafood.

The rate at which alexandrium fundyense appears seems to ebb and flow. There was a serious period of toxicity in the 10 years following 1978 and then again between 2003 and 2009. The rates have seemingly dropped since then, although no one is sure why and it is the topic of continued research.

Where Else Have Red Tides Appeared?

In the United States, red tides are most common along the coast of the Sunshine State, as well as the Gulf of Maine. However, they have appeared in numerous other locations throughout the last couple of centuries.

Some of the deadliest incidents of red tide occurred in Malaysia, and they have also appeared in Japan, the Philippines, and even the Netherlands.

Canada also reports red tide incidents. The first official Canadian case was recorded in British Columbia back in 1793, but there have been appearances at Prince Edward Island and elsewhere.

Can Red Tides be Predicted?

We are not able to predict red tides at present. However, by looking at water currents and wind movements, scientists are able to predict how they will spread once they have bloomed.

Are Red Tides Dangerous?

Some of the organisms that cause a red tide bloom produce toxins that can harm humans and sea life.

Where Florida red tides are concerned, the issue is a category of neurotoxins known as brevetoxins.

Brevetoxins are completely odorless and tasteless, but they can create a wealth of problems when inhaled, touched, or consumed.

Not only can direct contact lead to serious health implications, but humans can also ingest potentially harmful toxins by consuming fish and shellfish that have been in contact with these toxins.

To prevent such issues, seafood is often tested for toxins, although it’s not unheard of for contaminated seafood to make it into the supply chain.

History of Red Tides and Their Damage

During harmful algal blooms, it’s not uncommon to see dead marine animals wash up on the shore. There have also been a few reported issues in humans, although these are rare.

Some of the most serious issues recorded by historic red tides include:

  • 1530 to 1844: The first alleged incident of a red tide in Florida is said to have occurred in 1530. However, this has not been verified and most experts agree that the first recorded incident occurred in 1844.
  • 1916: The year of the famous shark attacks in New Jersey (ones that are thought to have inspired Jaws) was also the year of a major fish kill off the southwest coast of Florida.
  • 1972 to 1973: A red tide in Port Moresby is thought to have killed two people through poisoned seafood. It also destroyed a pearl farm.
  • 1976: 7 people died in Malaysian Borneo and many more suffered adverse reactions.
  • 1987: A red tide in Prince Edward Island caused over 7-figures in damage to the local economy.
  • 2013: Two individuals died after consuming contaminated shellfish following a red tide. The incident occurred in Sepanggar, Malaysia, and the locals were warned not to consume shellfish until the incident passed.
  • 2013: An incident in Sarasota Beach, Florida caused a major fish kill event and led to a number of respiratory problems among beach goers.
  • 2014: A huge red tide appeared in Florida, spanning over 90 miles in length and more than 60 miles in width.
  • 2015: 12 people were admitted to hospital in the Philippines following a red tide incident.
  • 2017 and 2018: Red tide events in Southwest Florida triggered fish deaths and also led to a number of dolphin and manatee deaths.
  • 2021: The Gulf Coast of Florida witnessed a red tide event that led to the death of millions of pounds of fish.

Why Are Red Tides a Problem?

Even if we discount the potential harm that red tides can cause to humans, there are other serious concerns about the frequency of this phenomenon.

Harmful algal blooms can devastate marine ecosystems. As noted above, there have been several incidents in which algal blooms have led to the death of millions of pounds of fish, as well as marine mammals like dolphins.

They take away potential income from local fisheries and also destroy farms. Local hospitals are also placed under great strain following an influx of patients with respiratory issues.

For small fishing towns and tourist resorts along the Florida coast, these outbreaks can be devastating, and it may take many months for them to fully recover.