The first time I saw a red tide licking the sands at the beach, I was mesmerized.
For as far as I could see, the waves were a a rusty red.
My initial thought was wow, but my second thought was what’s causing the ocean to look so red?
So I took a deep dive into everything you need to know about red tides.
What are Red Tides?
A red tide is when colonies of microscopic algae multiply at higher-than-usual levels and cause discoloration in the water. It basically looks like someone spilled red or brown coloring in the ocean.
Even though most people call these algae blooms red tides, the more scientifically sound term for these ocean events is harmful algal blooms (HABs) because they are not always visible.
Algae are simple aquatic plants that include larger species like seaweed and tinier single-celled species like Karenia brevis.
K. brevis is one of the best-known species of algae that causes harmful algal blooms.
Where Do Red Tides Happen?
According to the National Ocean Service, red tides have been reported in every coastal state in the United States. This includes the states that border the oceans and those that border the Great Lakes.
Red tides most commonly occur in three locations in the United States: off the coast of California, in the Gulf of Mexico, and in the Gulf of Maine. (Other locations like the Pacific Northwest and the Great Lakes are seeing an uptick, however.)
Red Tides in the Gulf of Mexico
HABs are probably most famous for occurring in the Gulf of Mexico, primarily off the coast of Florida.
K. brevis is the algae behind the red tides in the gulf. The algae are present at lower levels of concentration throughout the whole year but cause a red tide about once a year. You’ll mostly find these red tides in Florida, but sometimes storms will push the tides to Texas, Alabama, and Louisiana.
The central and southwestern coasts of Florida will typically see the most red tides.
Red Tides in California
The first red tide I saw was off the coast of Southern California in Huntington Beach.
The most common organism that causes red tides along the West Coast is Pseudo-nitzschia, according to the U.S. National Office for Harmful Algal Blooms.
Red Tides in the Gulf of Maine
The Gulf of Maine is another area of concern for red tides. It covers about 93,000 square kilometers and borders Maine, New Hampshire, Massachusetts, and parts of Canada.
Along the Atlantic coast, Alexandrium fundyense and Alexandrium catenella are the two organisms typically responsible for HABs. These are particularly notable because they can poison shellfish and sicken people who eat them. But more on that later.
When Do Red Tides Happen and How Often?
When red tides happen depends on several factors and the location you’re talking about. Let’s break it down by location.
- In the Gulf of Mexico along the coast of Florida, red tides happen roughly every year in the late summer or early fall.
- In Texas, blooms happen about every three years.
- In California, red tides happen approximately every three to seven years between early spring and late summer.
- The Gulf of Maine sees a red tide about every year in the spring and summer.
How Long Do Red Tides Last?
Like all the other questions in this article, the answer depends.
Red tides can last anywhere from days to weeks to months. Some even last longer than a year.
According to the Florida Fish and Wildlife Conversation Commission, most red tides in Florida last three to five months and extend hundreds of square miles.
In one notable red tide event, a harmful algal bloom lasted from October 2017 and dissipated sometime in early 2019.
California red tides typically only last one or two weeks, but they can be difficult to predict.
Can You Predict and Monitor Red Tides?
Unfortunately, scientists cannot predict the occurrence of a red tide right now. However, several organizations aim to research different methods of possibly predicting when and where a red tide might happen.
Predicting red tides would be a huge development, considering the massive impact they have on certain industries. During the 2018 red tide bloom, Florida lost an estimated $184 million from tourism.
The good news is that we can forecast the occurrence of harmful algal blooms. A prediction estimates when a red tide might happen with unseen data, while a forecast estimates when a red tide might occur based on real-time data.
Currently, the National Centers For Coastal Ocean Science forecasts HABs “based on understanding the causes of HABs and how they respond to changing weather and ocean conditions.”
They currently have forecasts for the Gulf of Mexico and Florida, the Gulf of Maine, and Lake Erie. Forecasts for the Pacific Northwest and California are coming soon.
Are Red Tides Becoming More Common?
Yes! Red tides are becoming far more common in the past few decades. The NOAA says red tides are 30 times more common now than in the 1960s.
The culprit behind the escalation of harmful algal blooms is us, of course. Chemicals we use in farms, sewage treatment plants, and factories eventually find their way into the oceans and lakes, helping algae grow quicker.
Climate change is another major contributor to red tides. The Washington Post did a great piece on how climate change causes red tides. Essentially, it causes warmer waters, more weather events for fertilizer to run off into the ocean, shallower waters, and higher carbon dioxide levels to help algae grow.
Are Red Tides Dangerous to Swim In?
Harmful Algal Blooms are called harmful for a reason. They can be very dangerous… but not every instance and not always for humans.
In California, some red tides are not at all harmful to humans. Other times, even nontoxic red tides have been associated with irritation around the eyes and mouth, potentially causing flu-like symptoms.
Florida officials say it’s safe for most people to swim in red tides. They do warn that those with respiratory illnesses may experience respiratory irritation.
This is even the case for those who are onshore. Wind can blow the microscopic organisms onto the beach where people can breathe them in.
Simply put: I would not swim in a red tide.
How Are Shellfish and Fish Affected?
The real danger of red tides is how it affects the animals living in the ocean. Red tides can cause massive die-offs of fish and poison sea creatures we commonly eat. The endangered manatee has been a frequent victim of red tides in Florida.
In places like Maine, a red tide can cause shellfish like clams, oysters, mussels, and scallops to become contaminated with toxins. When contaminated, shellfish are not safe to eat.
If someone accidentally ate a shellfish exposed to a harmful algal bloom, it could cause paralytic shellfish poisoning (PSP). Here is more from the Massachusetts government:
After ingestion, this poison immediately affects the nervous system, with symptoms usually occurring within 30 minutes. Severity depends on the amount of toxin consumed. Initial reactions are tingling of the lips and tongue, which spreads to the face, neck, fingertips, and toes. Headache, dizziness, and nausea follow.
In more severe cases, a person may have trouble breathing or suffer from muscular paralysis. Death from PSP has also been reported.
Fish are usually safe to eat as long as they are filleted.
Can Red Tides Be Stopped or Prevented?
Right now, there is nothing we can do to stop a red tide currently in progress.
Some scientists are looking into ways to treat red tides, including recruiting the natural enemies of algae, killing algae through an ozonation process, and more.
On the prevention side, it is far trickier. Red tides are naturally occurring and have been going on for millions of years. However, there are a lot of things that have caused the exponential growth of red tides.
To truly minimize the occurrence of harmful algal blooms, we would need to tackle climate change on every front: from minimizing the use of water-altering chemicals to stopping the use of fossil fuels.
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