What Causes Red Tides?

William West/AFP/Getty Images
William West/AFP/Getty Images

Every once in a while, the ocean turns the color of blood and scores of dead fish rise to the surface. The phenomenon might look like a biblical plague, but the source is far more mundane. It's just algae.

Red tides occur when there’s a sudden population boom among specific kinds of algae, which in enormous quantities become visible to the naked eye. They occur all over the world. In the Gulf of Mexico, the culprit behind red tides washing onto coastlines from Texas to Florida is usually a type of microscopic algae called Karenia brevis. It produces toxic chemicals that can cause symptoms ranging from sneezing and eye irritation to disorientation, vomiting, and breathing difficulties. It's often fatal for fish, shellfish, turtles, and other wildlife.

The water appears red because of the particular depth at which the algae live. Light waves don’t penetrate seawater evenly, and certain wavelengths travel farther than others. The algae that cause red tides grow at depths that absorb green and blue frequencies of light and reflect red ones.

Not all algal blooms are red; some are blue, green, brown, or even purple. Nor do all algae harm humans or animals. Why and how certain species of algae multiply like crazy and wipe out entire swaths of marine life is still a scientific mystery.

The worst red tide on record occurred in 1946, when a mass of algae stretching for 150 miles along the Florida coastline killed more than 50 million fish, along with hundreds of dolphins and sea turtles. Tourists shied away from the beaches as the bodies of dead sea creatures washed ashore. Smaller incidents are more common, but just as costly. In the past decade alone, fishing and tourism industries in the United States have had an estimated $1 billion in losses due to red tides—and the cost is expected to rise.

Editor's note: This story, which originally ran in 2015, was updated in August 2018.

Does Washing Your Fruits and Vegetables Really Do Anything?

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iStock

Washing produce is one of those habits that some people follow religiously and others shrug off altogether. If you're someone who struggles to find the motivation to cook in the first place, you might fall into the latter group. But cleaning your fruits and vegetables at home isn't just an outdated precaution: As Popular Mechanics reports, a thorough rinse could mean the difference between a meal that nourishes you and one that leaves you sick.

Produce is one common carrier of norovirus—a foodborne viral infection that triggers such symptoms as nausea, vomiting, and diarrhea. There's no way to know whether your lettuce is contaminated with harmful bacteria before it hits your plate, but cleaning it with plain tap water does make it safer to eat. According to USA Today, rinsing produce is effective enough to remove 90 percent of the pathogens left on it by the growing, harvesting, and shipping process. Rinsing is also a good way to remove any of the visible matter you don't want eat, such as grit and soil.

Cleaning your fruits and vegetables is definitely an improvement over eating them straight from your crisper drawer, but be warned that this isn't a foolproof way to avoid food poisoning. Water won't remove all the microbes living on the surface of your food, and even an extremely thorough rinse isn't enough to make produce contaminated with potentially deadly bacteria like E. coli safe to eat. But that doesn't mean the risk outweighs the benefits of including produce in your diet.

If you have a pile of veggies that need to be prepared for dinner, the best way to make them safer for consumption is to rinse them under cold water and rub them in a bowl of water, starting with the cleanest items and progressing to the produce that's more soiled. Give all the food a final rinse before moving it to the cutting board. Peeling the outside of your produce and cooking it when possible is another effective way to kill or remove stubborn bacteria.

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What's the Difference Between Pigeons and Doves?

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iStock

To the layman, the difference between pigeons and doves has something to with color, maybe. Or location. Or general appeal (doves usually get much better press than pigeons do). But what’s the actual, scientific difference between doves and pigeons?

As it turns out, there isn’t one. Paul Sweet, the collection manager for the department of ornithology at the American Museum of Natural History, says the difference is more linguistic than taxonomic.

“The word dove is a word that came into English from the more Nordic languages, whereas pigeon came into English from French,” Sweet tells Mental Floss.

Both dove and pigeon refer to the 308 species of birds from the Columbidae family, Sweet says. There’s no difference between a pigeon and a dove in scientific nomenclature, but colloquial English tends to categorize them by size. Something called a dove is generally smaller than something called a pigeon, but that’s not always the case. A common pigeon, for example, is called both a rock dove and a rock pigeon.

“People just have their own classification for what makes them different,” Sweet says. “So in the Pacific, for example, the big ones might get called pigeons and the smaller ones might be called doves, but they’re actually more closely related to each other than they are to other things in, say, South America, that are called pigeons and doves.”

The difference boils down to linguistic traditions, so feel free to tell people you’re releasing pigeons at your wedding or that you’re feeding doves in the park. Scientifically speaking, you’ll be correct either way.

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