When beluga whales want to communicate with each other, they just use the ol’ melon—a blubber-filled structure on their forehead. Researchers have found that the whales intentionally change the shape of the melon. That may convey different emotions or intentions—whether they want to play, mate, or just hang out.

Belugas live in and around the Arctic Ocean. They have a thick layer of blubber to protect them from the cold. And they don’t have a fin on their back, which allows them to easily glide below the ice.

They use their melon to send out pulses of sound, which helps them locate prey and predators and keep tabs on their fellow whales. They produce such a variety of sounds that they’re called “the canaries of the sea.”

Belugas are the only whales known to change the shape of the melon. Researchers studied what the shapes might mean. They spent a year observing two males and two females in an aquarium. And they followed up with shorter looks at more than 50 whales in a second location.

The scientists recorded more than 2500 melon shapes, which fit into five major categories. Almost all of the changes in shape took place when a beluga was around another whale. Many of the changes were associated with courtship, with males about three times more likely to make a change than females. But other changes were related to other social interactions, such as playing. So when a beluga has something to say, it just uses the ol’ melon.

The most powerful undersea volcano ever recorded had an impact on our entire planet—from pole to pole, and all the way to outer space. And it may continue to impact parts of the world for years.

The Hunga Tonga volcano is in the southern Pacific Ocean, well east of Australia. It staged a massive eruption in January of 2022. It blasted more than two cubic miles of rock and ash into the sky, and created tsunamis all across the Pacific. Shock waves in the atmosphere raced around the planet for days.

Satellites and balloons recorded effects at altitudes of up to about 180 miles. The eruption rattled the ionosphere—an electrically charged region that extends well into space. That disrupted some GPS signals and radio communications.

Hunga Tonga also blasted about 150 million tons of water vapor into the atmosphere. By late 2023, most of the water was still there. In fact, a layer of atmosphere a few dozen miles high contained more water vapor than had ever been seen there before.

In the southern hemisphere, the combination of water vapor and sulfur from the eruption damaged the ozone layer during the winter and spring of 2023.

And one study found that the aftermath of the eruption could affect the climate in parts of the world through 2029. North America could see warmer winters, while the winters in Scandinavia and parts of Australia could be colder and wetter—lingering effects of a monster volcano.

One of the changes that goes along with aging is hair color. Red, blonde, black—regardless of the original color, our hair almost always turns gray or silver.

Fish don’t have hair, but many of them do change color as they age. They can take on different color schemes as they move through different stages of life.

Fish change color for many reasons. Some of the changes happen in a flash—a fish might blend into the background to protect itself from predators. Other changes are more gradual. A fish might change color when it switches gender, for example.

Many fish keep the same basic scheme throughout life—especially those that spend their lives in the open ocean. The ones that are more likely to change color as they age are those that move around—they’re born in one place, but they shift habitats as they grow and mature.

Salmon, for example, have stripes when they hatch, in rivers and streams. When they move out to sea, though, they take on a smoother, silvery tone. American eels, on the other hand, are colorless when they hatch, in the open ocean. But as they mature, and move into rivers and streams, they turn dark on top and light-colored on the bottom. And when they return to the ocean to spawn, they turn silvery bronze.

And in some species, only some members change color as they age. Only males of the bluehead wrasse adopt the namesake color, and only when they mark out a territory—a colorful signal that they’re ready to take a mate.