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As most people are aware, around 70% of Earth's surface is covered by water. In total, there are approximately 1.3 billion cubic kilometers (332.5 million cubic miles) of water, and the vast oceans, seas, and rivers that contain it remain among the least understood areas of our planet—and so do the fascinating creatures that inhabit them.
10. Colossal Squids Use Their Brains to Digest Food
The colossal squid, scientifically known as Mesonychoteuthis hamiltoni, was once thought to be a mythical creature, with only a few real-life sightings. In 2007, however, the largest specimen ever recorded was captured by New Zealand fishermen in the Ross Sea near Antarctica. This massive squid measured an astonishing 10 meters (33 feet) in length and weighed nearly 450 kilograms (1,000 pounds). It was brought to New Zealand for research, and scientists discovered something extraordinary: Its digestive system runs directly through the center of its brain.
The brain of the colossal squid resembles a doughnut—a ring of flesh with a hole in the center. When it consumes prey, the esophagus funnels the food through the brain, where nutrients are absorbed before reaching the stomach. These gigantic squids live in the cold depths of the ocean, and due to their sluggish metabolism, they require very little food to sustain themselves. In fact, this half-ton creature only needs about 30 grams (1 oz) of food daily—roughly the weight of a single AA battery.
9. Piranha-Resistant Fish Armor
Piranhas, the razor-toothed predators of the Amazon River, have few natural enemies and a constant supply of potential prey. While a lone piranha may fall prey to a dolphin or a cormorant, their habit of swimming in large schools protects them from most predators, allowing them to live almost without fear. Consequently, other Amazonian fish have evolved defenses against these aggressive neighbors, including the largest fish in the Amazon—the Arapaima gigas, or giant arapaima—which has developed its own form of armor.
Giant arapaima are massive creatures, reaching weights of up to 130 kilograms (300 lbs) in adulthood. However, as Teddy Roosevelt observed, even their immense size is no deterrent to a school of piranhas. To protect themselves, these giant fish evolved an armored skin, made up of two layers. The outer layer consists of a tough, mineralized shell, while the inner layer is softer with a complex collagen structure that forms rotating stairways. When a piranha’s tooth bites down on the outer shell, the stairway-like structures flex and twist to absorb the impact without breaking. It’s like striking a pillow rather than a pane of glass—the pillow returns to its original shape.
8. The Invisible War
The most prevalent life form in the ocean is one you'll never notice—a group of bacteria known collectively as SAR11. Found across every ocean, from the Arctic to the tropics, these bacteria are incredibly efficient at their task—transforming dissolved carbon into CO2. The ocean's most widespread predator also resides at the microscopic level—a related group of viruses called pelagiphages. These viruses are in a constant battle with the SAR11 bacteria.
This is a fierce evolutionary arms race. In 1990, the SAR11 bacteria were first observed, though they were largely overlooked at the time. Their behavior seemed unremarkable—they’re just abundant. But earlier this year, during a standard water test off the Oregon coast, a large number of SAR11 cells were found dead. Swimming in the same water were previously unknown pelagiphage viruses, and researchers watched as these viruses slaughtered the remaining SAR11 cells in real-time.
The SAR11 bacteria are so skilled at sharing genetic information that they’ve stayed one step ahead of the pelagiphages, continuously evolving to fend them off. But the viruses are not far behind. A completely new subfamily of pelagiphages has already evolved to target the more advanced SAR11 strains. It’s a microscopic war unfolding right before our eyes.
7. Catfish Possess Around 100,000 Taste Buds
Humans typically have between 2,000 and 8,000 taste buds, concentrated around the mouth. But catfish take things to a whole new level, boasting around 100,000 taste buds scattered across their bodies. Essentially, a catfish is like a giant swimming tongue. Each taste bud is about 50 nanometers wide (50 billionths of a meter, or 164 billionths of a foot), and the bigger the fish, the more taste buds it has. Larger catfish can sport over 175,000 taste buds all over their bodies.
Why would an animal, particularly one that lives in muddy ponds, need such an acute sense of taste? Catfish use it to hunt. As you descend deeper into the water, visibility diminishes, so sight isn’t always effective for bottom dwellers like catfish. With their taste buds, they can “taste” prey from meters away, much like how a wolf detects a scent. Thanks to the many taste buds all over their bodies, catfish can pinpoint the location of their prey by sensing which parts of their body feel the strongest taste. Most of these taste buds are concentrated near the front of the catfish, helping it zero in on its target once it’s oriented in the right direction.
Although catfish do rely on their eyes, research has shown that their taste buds are far more important for hunting than vision. If you take away a catfish’s eyes, it will still be able to find food. But if you remove its taste buds, it’s essentially blind.
Photo credit: Lukas Jurek
6. Dolphins Have the Ability to See Through Other Creatures
Dolphins, as we all know, use sonar for a variety of tasks such as navigation, hunting, communication, and more. This process, called echolocation, involves dolphins emitting high-frequency sound bursts generated by pushing air through a series of tissues near their blowholes. A fat-filled sac beneath their jaws captures the returning sound waves and sends them to the dolphin’s inner ear, where the information is relayed to the brain, creating an 'acoustical holographic image'—essentially a mental picture of the ocean ahead.
The frequency of these echolocation bursts—ranging from 40 to 130 kHz—isn’t ideal for traveling long distances in water, but its short wavelength is perfect for passing through soft tissues. This means the sound waves move through the soft bodies of fish and dolphins and only bounce off denser surfaces—like bones and cartilage. In other words, it works much like X-ray vision, enabling dolphins to peer inside other animals. Observations suggest dolphins can even look into a shark’s stomach to check if it’s full, or detect if a female dolphin is pregnant. Dolphins have also been seen clicking along the seafloor to find hidden fish buried beneath up to 1 meter (3 feet) of sand.
5. Swellsharks
While most sharks intimidate predators simply by being sharks, they still have their share of enemies, and the smaller the species, the more dangerous it becomes. The swellshark, for example, is one of the smaller varieties, growing to only about 1 meter (3 feet) in length, roughly the size of a small doberman. These sharks are bottom feeders, opting to ambush crabs and unsuspecting cuttlefish rather than chase faster fish. On a particularly daring day, they might even raid lobster traps. When it comes to defense, the swellshark is a master of camouflage: When threatened, it sucks water into sacs around its belly, causing it to inflate to twice its normal size.
But then, the swellshark does something even more bizarre—it curves its body into a crescent, catches its tail in its mouth, and turns itself into a giant, inflated ring. This makes it incredibly difficult to eat. Plus, since swellsharks typically hide in rocky crevices, the inflation helps wedge them firmly into their safe spots. So, even if a predator manages to catch one, it can only get a small bite. It’s often called the most awkward shark in existence.
4. Pompeii Worms Have A Living Shield
“The hottest creature on Earth, but also the most challenging to study,” is how the Pompeii worm, or Alvinella pompejana, has been described. These worms live at an astonishing 2,500 meters (8,000 ft) below the ocean's surface, near volcanic vents that heat the surrounding water to a scorching 80°C (176°F). The problem? They tend to die when brought to the surface. For years, scientists believed the Pompeii worm was the most heat-resistant creature on the planet. Reaching a length of about 13 centimeters (5 inches), these worms live in tubes attached directly to the sides of “black smokers”—volcanic exhaust vents on the East Pacific Rise.
However, their title as the heat champions has been contested. Using pressurized capsules, researchers were able to bring a few worms to a lab, only to find that after just 10 minutes of exposure to temperatures of 50°C (122°F), the worms perished, their tissues becoming as hard as a boiled egg. They had been cooked. But, the fact that Pompeii worms thrive in these extreme conditions led scientists to dig deeper. What they discovered was fascinating: a layer of bacteria surrounding the worms acted as a living shield, absorbing some of the heat from the scalding water, much like a fireman’s blanket. In exchange, the worms produced a mucous layer that nourished the bacteria—creating a perfect symbiotic relationship.
3. Google Street View: Oceans
Google Street View is a widely-used feature on Google Maps that allows you to view any location from a street-level perspective. In 2007, Google deployed a fleet of cars worldwide to capture images of literally everything. These images were then stitched together into a continuous string, enabling users to 'walk' any route with just a click. While this was groundbreaking at the time, it’s now considered somewhat old news and far less thrilling.
Street View: Oceans is a similar concept, but instead of peering into your ex-girlfriend's house, you can now explore the Great Barrier Reef or any number of underwater locations across six oceans. New locations are being added rapidly, but currently, the program features reefs around the Galapagos Islands, Heron Island, Wilson Island, and Hanauma Bay, among others. This initiative serves as both a publicity campaign and a scientific endeavor—while the public enjoys the virtual tour, scientists use the images to monitor the growth and decline of the world’s most vital coral reefs, which host 25 percent of all marine life.
2. The World’s Largest Migration Happens Every Day
The Sargasso Sea stands out as one of the most unusual bodies of water on Earth. Lacking defined borders, it is held in place by converging currents, despite being situated right in the middle of the Atlantic Ocean. Essentially, it’s a body of water within another body of water—where the Gulf Stream, the North Atlantic Current, and the Canary Current meet, creating a calm center. Sailors once dubbed it the 'Sea of Lost Ships' because the area is so eerily calm that ships could get trapped there for days or even weeks.
Above all, the Sargasso Sea is a remarkably self-sustaining ecosystem. The sargassum, a floating seaweed that blankets the surface of the sea, offers both food and shelter to thousands of species, and in turn, these species nourish the sargassum with their waste. The layers of marine life in this sea range from surface creatures to deep-sea organisms living over 5,000 meters (16,000 ft) below. At night, it becomes the stage for the largest migration on Earth—over 5,000 species of sea creatures, numbering in the millions, rise up from the depths to feed, only to descend again before dawn.
Photo Credit: NOAA
1. Anguilla Eels Can Walk On Land
Anguilla eels, also known as European eels, inhabit the lakes and rivers of northern Europe and the UK. They can grow up to nearly 2 meters (6.5 ft) in length, though they are typically smaller, usually around half that size or less. But these eels don’t always stick to the water—they can leave it and crawl across dry land for short distances. They do this for two main reasons: first, to feed on insects and earthworms, and second, to migrate.
Anguilla eels spend around 20 years in the same lake. However, their life journey begins and ends 6,500 kilometers (4,000 miles) away, in the Sargasso Sea. To travel from their freshwater homes in Europe to the Atlantic, these eels use a mysterious navigation method that has yet to be fully understood. If they encounter obstacles, like dams, they don't hesitate to leave the water and slither across fields and forests to find another stream or river. Environmentalists are using this fascinating skill to create 'climbable ladders' on dams and weirs to help the eels complete their migrations. On a more unsettling note, the larger relatives of anguillas, known as conger eels, are also capable of crossing land and have been known to attack people.
