What Is a Red Tide?

If you reside near a coastal region, then you might have heard about red tides occasionally. Despite their pleasant-sounding name, red tides often come with serious warnings.

Red tide is a commonly used but misleading term for a natural occurrence that regularly happens along most coastal areas. Instead of red tide, scientists refer to these events as harmful algal blooms or HABs.

Seawater always contains small plant-like organisms known as algae. Normally, algae can only be seen through a microscope. Under specific conditions, algae can begin reproducing rapidly. This causes the algae population to grow at a fast pace or “bloom.” During an algal bloom, a single gallon of seawater can contain millions of algae.

Not all algal blooms are harmful. However, some algae produce harmful substances called toxins. For instance, the Florida Gulf Coast frequently experiences harmful algal blooms of a specific type of algae called Karenia brevis, which produces toxins known as brevetoxins.

Blooms of Karenia brevis can change the color of the water, turning it yellow, orange, pink, brown, or red. This change in color is likely what led some people to use the term red tide. Nevertheless, scientists do not prefer the term red tide for several reasons.

Harmful algal blooms do not always change the color of the water, and when they do, it is not always red. Furthermore, harmful algal blooms are not related to tides. This is why scientists prefer the more accurate term harmful algal bloom instead of red tide.

Harmful algal blooms are called harmful because the toxins produced by the blooming algae can kill millions of fish and other marine organisms. One clear sign of a harmful algal bloom is a beach covered with dead fish.

Harmful algal blooms can also be dangerous for humans. People have been known to become ill from consuming shellfish that feed on the toxic algae. Some experts also believe that there may be negative effects associated with breathing the air near or swimming in water during a harmful algal bloom.

Due to the impact on marine and human health, as well as shoreline quality and the fishing industry, scientists are working to learn more about the causes of harmful algal blooms. Some believe that they are simply natural occurrences caused by the seasonal movement of ocean currents. Others believe that human factors, such as pollution, may also contribute.

Algal blooms of non-toxic algae are not necessarily harmful. In fact, they are often beneficial because they provide more food – the algae – for the marine life that feeds on them.

Scientists have discovered that even harmful algal blooms may have benefits. For example, despite the death of some fish, scientists have observed that other marine populations appear to increase. This has led some scientists to theorize that harmful algal blooms may be one of nature’s ways to balance the populations of various marine species.

Try It Out

Are you ready to learn more about red tides? Make sure to explore the following activities with a friend or family member:

  • Although a red tide has many negative effects, there is a unique positive outcome. In certain areas, bioluminescent phytoplankton create a captivating light display at night. As they are tossed by the waves, they emit flashes of light. When the evening surf arrives, beachgoers are treated to a natural light show courtesy of Mother Nature. Take a look at these videos showcasing the bioluminescent phytoplankton in action: + LaJolla, California + San Diego, California.
  • If you were a scientist tasked with preventing red tides, how would you approach researching the subject and developing solutions? What inquiries would you have? How would you gather data? How could you assist fish in defending themselves against harmful algal blooms? Have fun thinking like a scientist! Share your ideas with a friend or family member.
  • Interested in getting some hands-on experience with algae? With the assistance of a friend or family member, go online and explore The Algae-in-a-Bottle Experiment. Gather your materials and enjoy experimenting with the cultivation of algae in a bottle!

Sources of Wonder

  • http://www.whoi.edu/redtide/ (accessed on 8 May, 2023)
  • http://oceanservice.noaa.gov/facts/redtide.html (accessed on 8 May, 2023)
  • http://www.marine.usf.edu/pjocean/packets/sp01/sp01u3p2.pdf (accessed on 8 May, 2023)

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