Category: Marine Biology

The Fish that Sees Red

5/19/2022

Steve Jenkins

Making Sense of the Natural World

Have you ever noticed how photographs of underwater scenes have a bluish tint? Sunlight is made up of a rainbow of colors, but when it enters the water the reds and yellows in the light are quickly filtered out. The blues and greens penetrate deeper into the water and give those watery scenes their peculiar cast. Because there is very little red light in the deep sea, most of the animals that live there have never evolved the ability to see the color red. This is why many deep-sea animals are red. In the depths of the ocean, a creature that can’t be seen is safe from many predators.

There is an unusual fish that takes advantage of its fellow sea creatures’ colorblindness. The stoplight loosejaw, a member of the dragonfish family, can see the color red. Not only that, but it has a patch on its face that glows red. It also has a glowing green spot on its face, which is probably used to communicate with other dragonfish. These red and green patches explain the “stoplight” part of this fish’s name. The “loosejaw” comes from this fish’s ability to open its mouth extra wide and swallow large prey. Scientists think that the open structure of the lower jaw allows the fish to close its mouth quickly, making it difficult for prey to escape. Relative to its size, the stoplight loosejaw has one of the widest gapes of any fish, with a lower jaw measuring one-quarter of the fish’s length. It’s not easy for animals that live in the dark waters of the deep sea to find prey. Many of them, including the stoplight loosejaw, have large mouths and sharp fangs that help ensure that their prey cannot escape.

Below about 650 feet (200 meters), very little sunlight penetrates the ocean. Below 3,300 feet (1,000 meters), the only light is that produced by living creatures. Almost all deep-sea creatures can bioluminescence, or make their own light. But the light they produce is usually blue or green. When the stoplight loosejaw switches on its red spotlight, other creatures in the water are illuminated. Being blind to the color red, they don’t realize that they’ve been spotted. Dragonfish are not known as picky eaters. If one of the lit-up animals is a fish, shrimp, or other suitable prey, the stoplight loosejaw quickly grabs it and swallows it.

The stoplight loosejaw's attributes include a red spot, hinged jaws, and needle-like teeth. Illustration by Steve Jenkins

There are two kinds of stoplight loosejaws. The Northern (Malacosteus niger) shown here and the Southern. Together they are found everywhere in the world except the North and South Poles. Wikimedia Commons

Steve Jenkins has written and illustrated more than forty
nonfiction picture books, including the Caldecott Honor–
winning What Do You Do with a Tail Like This? and the
Boston Globe Horn Book honor–winning The Animal Book.
His most recent books are Apex Predators: Top Killers Past
and Present and Who Am I?, an animal guessing game
written with Robin Page.

MLA 8 Citation
Jenkins, Steve. "The Fish That Sees Red." Nonfiction Minute, iNK Think Tank, 6
June 2018, www.nonfictionminute.org/the-nonfiction-minute/
The-Fish-that-Sees-Red.

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To the Ends of the Earth

1/23/2020

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Jim Whiting
The Running Encyclopedia

In the early 1900s, becoming the first to reach the South Pole was a huge source of individual and national pride. English explorer Ernest Shackleton came within 97 miles of that goal in 1909 before being forced to turn back.

Fellow Englishman Robert Scott made well-publicized plans to succeed where Shackleton had failed. He was therefore dismayed to learn that Norwegian Roald Amundsen had his own secret plan to reach the Pole. Amundsen hadn’t even told his crew members where they were going until they were at sea.

The two expeditions landed in Antarctica at roughly the same time and spent months preparing for their respective treks. Amundsen departed on October 18, 1911. He was fortunate to encounter relatively good weather. On December 7, he passed the southernmost point Shackleton had reached. One week later, on December 14, he and his four men stood on the South Pole. Each man grasped the Norwegian flag. They celebrated in the evening with seal meat and cigars. Before returning, they erected a tent and put letters for Scott and Norwegian King Haakon inside. Amundsen and his men arrived back at their starting point in late January and sailed to Tasmania, where Amundsen sent a cable trumpeting his accomplishment. Even though the response was mostly favorable, some people in England thought Amundsen had played a dirty trick by being so secretive about his plans.

Meanwhile, Scott and his four men left from their base three weeks after Amundsen. They encountered some of the worst weather Antarctica could throw at them. Several times they had to stay in their tents for extended periods, eating valuable food. They finally arrived at the Pole on January 17, only to have their triumph replaced with bitter disappointment. They found Amundsen’s letters and knew they were five weeks too late.

Their difficulties worsened on the way back. Two men died from cold, hunger, and exhaustion. Scott and the two others made what proved to be their final camp on March 19, confined to their tent by horrific weather. They were about 10 miles from a food depot that would have ensured their survival, but couldn’t reach it. Searchers found their frozen bodies eight months later.

Amundsen died in 1928 in a plane crash during a rescue mission in the Arctic Ocean. Shortly before his death, he told a journalist, “If only you knew how splendid it is up here, that’s where I want to die.”

Can you guess which portrait is of the free-wielding Roald Amundsen and which is the careful planner Robert Scott ? Hint: Credit for the photo at the left is National Library of Norway.

Amundsen's group admires their victory display as they prepare to leave the South Pole.

And here is Scott's party arriving at the Pole. What disappointment for them to reach the end of the earth only to find this tent topped by the Norwegian flag waiting for them.

Map showing the polar journeys of the Scott's expedition (green) and Amundsen's expedition (red) to reach the South Pole. Wikimedia Commons

Aristotle discovered Antarctica nearly 2,500 years ago, though no one set foot on the continent until the 1800s. Exploration went into high gear several decades later during the Heroic Age. The peak came in 1911 when Norwegian Roald Amundsen reached the Pole, followed soon afterward by the tragic deaths of Englishman Robert Scott and four companions. This is one of many of Jim Whiting's books.

MLA 8 Citation
Whiting, Jim. "To the Ends of the Earth." Nonfiction Minute, iNK Think Tank, 18
Jan. 2018, www.nonfictionminute.org/the-nonfiction-minute/
To-the-Ends-of-the-Earth.

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Who Eats the Largest Jellyfish in the World -- and Enjoys It?

9/20/2019

4 Comments

Stephen R. Swinburne

Lifelong Naturalist

Lion’s mane jellyfish can grow seven feet wide with tentacles reaching a length of 100 feet. That’s the same length as a blue whale! Their bodies are 98 percent seawater. They live in the cold, boreal waters of the Arctic, northern Atlantic and northern Pacific Oceans. Slowly pulsating ocean currents carry the big jellies great distances. The long trailing, stinging tentacles capture and tear apart their prey. Swimmers beware when currents sweep lion’s manes close to shore. Their stings cause red swollen welts, and severe body contact with a lion’s mane jellyfish may be deadly.

What animal can happily and safely slurp down a lion’s mane jellyfish as if it were a big bowl of Jello™? The leatherback sea turtle!

Adult leatherbacks are the largest reptiles on earth today, averaging seven feet long. As the planet’s biggest turtle, they range from the Arctic Circle south to Antarctica, and they swim, on average, more than 6,000 miles each year. And they love lion’s mane jellyfish. As a matter of fact, lion’s mane jellyfish make up almost their entire diet. How can a seven-foot long sea turtle consume a creature armored with a hundred feet of stinging tentacles?

Often referred to as Earth’s last dinosaur, leatherback sea turtles have lived on the planet for millions of years, surviving ice ages and major extinctions. For an animal to live that long on a diet of giant blobs of gelatinous saltwater, it better be very very good at tackling and consuming its delicious but dangerous meals of giant stinging jellyfish. And, it better have developed some cool adaptations over the ages. Here’s how they do it

First off, a sharp pointed lip acts like a hook so the turtle can snag the jellyfish and hang onto it.

Second, the turtle’s mouthful of backward-pointing spines prevents the jellyfish from escaping. A scientist once said to me, while looking into the mouth of a leatherback, “It’s the last thing a jellyfish will ever see!”

Once the leatherback has consumed dozens and dozens of jellyfish, there’s the problem of all that salt in its diet. Eating too much salt will cause dehydration. No problem for the leatherback! The turtle is perfectly adapted to rid its body of all that excess salt. Salt or lacrimal glands, located near their eyes, allow leatherbacks to secret saline tears—and then they cry them away.

So the largest marine reptile on earth evolved by getting better and better at eating the most unlikely diet, the largest jellyfish on earth.

Lion's mane jellyfish. Wikimedia Commons. Photo by Dan Hershman

Leatherback turtle.

This photo of Dr. Kimberly Stewart photographing a nesting leatherback gives you an idea of the size of the turtle. Photo by Claudia Lombard, U.S. Fish and Wildlife Service, Sandy Point National Wildlife Refuge, US Virgin Islands

Steve Swinburne has written a book on sea turtles. To see information about the book as well as a study guide and video and picture gallery, click here.

Steve Swinburne is a member of iNK's Authors on Call and is available for classroom programs through Field Trip Zoom, a terrific technology that requires only a computer, wifi, and a webcam. Click here to find out more.

MLA 8 Citation
Swinburne, Stephen R. "Who Eats the Largest Jellyfish in the World -- and Enjoys It?" Nonfiction, iNK Think Tank, 12 Oct. 2017, www.nonfictionminute.org/the-nonfiction-minute/who-eats-the-largest-jellyfish-in-the-world-and-enjoys-it.

4 Comments

The Fish that Sees Red

To the Ends of the Earth

Who Eats the Largest Jellyfish in the World -- and Enjoys It?

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