The ocean covers most of our planet, yet we have mapped more of the Moon than our own seafloor. These stories introduce sea creatures with strange survival tricks, the astonishing world of the deep sea, the scientists and daredevils who explored it, and natural wonders from glowing bays to trenches deeper than Everest is tall. Meet a shark older than the United States, a jellyfish that never truly dies, and the ordinary rock an otter keeps for life.
Every tile in a Oceans and Sea Life game carries one of these. Open one to read it now, or leave them for the board to hand you.
Creatures
nine stories
1The jellyfish that reverses old age
On the tile: Immortal Jelly1980s
Turritopsis dohrnii was described in 1883, but its strangest ability went unnoticed for a century. When this tiny jellyfish is injured, starved or simply aging, it does not have to die. It shrinks into a blob, settles on the seafloor and turns back into a polyp, the rooted stage it grew from. Biologists call this transdifferentiation: mature cells reprogram themselves into completely different types. Researchers stumbled on the reversal in the 1980s, after leaving some of the jellyfish unattended in the lab over a weekend. The cycle can repeat, and in perfect conditions the jellyfish might never die of old age.
A mantis shrimp's club-shaped forelimb strikes at about 50 miles an hour, so fast that the water in front of it boils into a cavitation bubble, a pocket of vapor that collapses with a tiny flash of light. In captivity, these shrimp have been known to break the glass walls of their tanks. Biologist Sheila Patek clocked the true speed in 2004 with a high-speed camera the BBC rented for her team while making a TV series, and measured accelerations of up to about 10,000 times the force of gravity. Later force measurements showed that each strike hits prey twice: once with the club, once with the collapsing bubble.
Sea otters are among the few animals that use tools. When a meal comes in a hard shell, an otter floating on its back may crack it open with a rock, then tuck a good stone into a pouch of loose skin under its forearm and keep it for many dives. A 2024 study that tracked 196 wild otters off California found that tool-using females, despite their weaker bite, could eat prey up to 35 percent harder than males did, and that tool users of both sexes had less tooth damage. That matters, because an otter whose teeth are too worn or damaged can starve.
For centuries, traders sold narwhal tusks in Europe as unicorn horns; Queen Elizabeth I was said to have paid 10,000 pounds for one, the price of a castle. The tusk is not a horn at all. It is an overgrown tooth, usually the left one, that spirals out through a male narwhal's upper lip and can grow nearly 10 feet long. In 1638, the Danish naturalist Ole Worm showed a narwhal skull with its tusk still attached, and the unicorn-horn trade began to fade. Scientists now think the tusk also works as a sensory organ, with fine channels that let seawater reach nerves inside.
Greenland sharks grow only about a centimeter a year and do not reach sexual maturity until roughly age 150, so scientists needed an unusual clock to age them. In 2016, researchers radiocarbon-dated the eye lenses of 28 female Greenland sharks, because the center of each lens forms before birth and its proteins never change afterward. The largest shark studied, about 5 meters long, was estimated at roughly 392 years old, give or take 120 years, making the species the longest-lived vertebrate known, ahead of the bowhead whale at an estimated 211 years.
6An octopus that fits through a hole the size of a lemon
On the tile: Giant Octopus
A giant Pacific octopus has no bones. Its only hard part is its beak, so if the beak fits through an opening, the rest can follow; a full-grown adult can squeeze through a hole the size of a lemon. Each of its eight arms has its own small cluster of nerve cells and can act on its own, which is why a NOAA lab blog credits the octopus with nine brains. At that lab in Kodiak, Alaska, staff taught an octopus named Pi to open jars. He could recognize faces and had moods: some days he wanted to play, others he preferred to be left alone.
Many deep-sea anglerfish males are far smaller than females and cannot feed themselves as adults. When a male finds a mate, he bites onto her body and never lets go. Their tissue fuses, their blood vessels join, and over time the male loses his eyes, fins and most internal organs, surviving as a permanent sperm supply nourished by the female's blood. In August 2016, explorers in a submersible off Portugal's Azores islands filmed such a pair alive for the first time: a six-inch female fanfin seadevil, Caulophryne jordani, with a tiny male fused to her body. Before that, scientists knew the pairing only from dead specimens.
Vampyroteuthis infernalis means vampire squid from hell, a name that suggests a bloodthirsty hunter. The reality is far gentler. The toothlike spines under its cloak are soft and fleshy rather than sharp, it does not feed on blood, and it is not even a true squid, but the last survivor of an ancient branch of the cephalopod family tree. Instead of chasing prey, it drifts through the ocean's oxygen-poor middle depths and uses two long filaments to gather marine snow, the drifting flakes of dead plankton, algae and waste that fall from above, making it the only cephalopod known not to hunt living prey.
The Portuguese man o' war looks and stings like a jellyfish, but it is not one, and it is not even a single animal. It is a siphonophore: a colony of specialized, genetically identical individuals called zooids, most of which cannot survive alone. Some zooids capture prey with stinging tentacles that average about 30 feet long, others digest it, and others reproduce. Above them all rides a gas-filled float that acts as a sail, so the colony goes wherever wind and currents push it. That sail is why the animal was named after a warship.
The Challenger Deep, at the southern end of the Mariana Trench in the western Pacific, is the deepest known point in any ocean. A 2010 multibeam sonar survey by the University of New Hampshire measured it at about 10,994 meters, or 6.8 miles, plus or minus roughly 40 meters. To picture that depth, NOAA points out that if Mount Everest were placed at the bottom of the Challenger Deep, its summit would still sit more than a mile underwater. Pressure at the bottom is roughly 1,000 times what it is at sea level.
In February 1977, geologists diving in the submersible Alvin to the Galapagos Rift were not looking for life; no biologist was even on the expedition, since the deep sea was thought to be a desert. More than 8,000 feet down, pilot Jack Donnelly and scientists Jack Corliss and Tjeerd van Andel found warm water shimmering out of cracks in fresh lava, surrounded by white clams up to a foot long, brown mussels, white crabs and a purple octopus. Water samples reeked of hydrogen sulfide, fuel for a food chain built not on sunlight but on chemosynthesis, microbes turning chemicals into energy.
Before 2004, scientists knew the giant squid only from dead or dying animals that washed ashore or were caught in fishing nets. On September 30 of that year, zoologist Tsunemi Kubodera and Kyoichi Mori of the Ogasawara Whale Watching Association lowered a baited camera 900 meters down near Japan's Ogasawara Islands, where sperm whales hunt. A giant squid attacked the bait, snagged a tentacle on the hook and struggled for more than four hours before the tentacle tore off. By then the camera had taken the first photographs of a live giant squid in its own habitat.
The deep seafloor usually lives on marine snow, a slow drizzle of organic particles from above. Then a whale dies and sinks, and one carcass can deliver as much food as several thousand years of that snow. Scavengers strip it to the bone within months, but at least one whale-fall community has apparently lasted more than 50 years. On a whale skeleton almost three kilometers down in Monterey Canyon, researchers found new species of bone-eating worms, named Osedax, Latin for bone devourer. Fossil clams found with 30-million-year-old whale bones suggest these feasts are ancient.
In 2022, researchers filmed a snailfish of the genus Pseudoliparis 8,336 meters down in the Izu-Ogasawara Trench off Japan, the deepest any fish has ever been recorded. It beat the previous record, a Mariana snailfish filmed by the same team in 2017, by 158 meters. The fish was an extremely small juvenile, swimming up to a baited camera. Snailfish cope with the crushing pressure thanks to gelatinous bodies, no swim bladder and gaps in their skulls. Expedition leader Alan Jamieson puts the depth limit for any fish at around 8,200 to 8,400 meters.
After a B-52 bomber collided with a refueling tanker over Palomares, Spain, in January 1966, one of its four hydrogen bombs fell into the Mediterranean and vanished. The Woods Hole submersible Alvin was flown to Spain, and after weeks of searching, its pilots found the bomb on a steep slope about 2,500 feet down. The first lift failed: the hook bent, and the bomb slid to about 2,800 feet. Alvin found it again, and in early April an unmanned Navy vehicle, CURV, brought it up. A memo afterward noted that the search had exposed Alvin's lack of a working navigation system.
In 1942, near Guadalupe Island off Baja California, wartime researchers Russell Raitt, R. J. Christensen and Carl Eyring watched their echo sounder show the seafloor at 1,500 feet, in water known to be 12,000 feet deep. The phantom bottom was real, and because it scattered sound, it became the deep scattering layer. Scripps oceanographer Martin Johnson predicted that if it was alive, it would rise at evening and re-form by morning. A round-the-clock trip in June 1945 proved him right. The layer is a crowd of fish, squid and jellyfish that hide deep by day and rise at night to eat.
8Most animals in the deep sea make their own light
On the tile: Deep-Sea Glow2017 study
Below about 300 meters, the ocean is essentially pitch black, but many of its animals bring their own light. In a 2017 study, researchers at the Monterey Bay Aquarium Research Institute went through video from 240 dives by robotic submarines in Monterey Bay and tallied more than 350,000 animals living between the surface and 4,000 meters down. About three-quarters of them could produce their own light. Among jellyfish and siphonophores, 97 to 99.7 percent could glow, while only about half of the fishes, squids and octopuses could.
The colossal squid has the largest eyes of any animal ever studied, and possibly the largest in the history of the animal kingdom. In a living colossal squid, each eye measures about 27 centimeters across, roughly the size of a soccer ball, with a lens the size of an orange. Why so big? A 2012 study by Dan-Eric Nilsson of Lund University and colleagues argued that such giant eyes let giant and colossal squid spot sperm whales, a major predator, from a distance in the dark, by the faint glow of tiny animals a swimming whale disturbs.
Before 1943, divers who wanted freedom underwater had few good options: heavy helmets fed by surface air hoses, or oxygen rebreathers that turned toxic at depth. Engineer Emile Gagnan had built a demand valve so cars could run on cooking gas during wartime fuel shortages in France; Jacques Cousteau saw that the same valve could feed a diver air only when he inhaled. The two adapted it into the Aqua-Lung, and Cousteau took his first real dive with it in the Mediterranean in June 1943. He and two friends made more than 500 test dives that year. It became the first open-circuit scuba gear to win worldwide commercial success.
On August 15, 1934, naturalist William Beebe and engineer Otis Barton descended off Bermuda inside the bathysphere, a hollow metal ball less than five feet across and weighing about 5,000 pounds, hanging from a ship on a single steel cable. They reached 3,028 feet, a new record. A telephone line carried Beebe's descriptions of the creatures outside the windows up to the ship. National Geographic's editor, Gilbert Grosvenor, had pledged $10,000 for more dives if the pair reached half a mile down, and four days earlier they had stopped short at 2,510 feet. Their record stood for fifteen years, until Barton broke it himself in 1949.
On January 23, 1960, Jacques Piccard and U.S. Navy Lieutenant Don Walsh climbed into the bathyscaphe Trieste and began a nearly five-hour descent to the Challenger Deep, the deepest point in any ocean. About 30,000 feet down, the crew heard a loud crack: an outer Plexiglas window had fractured under the pressure, though the cabin held. At the bottom, nearly seven miles beneath the surface, they reported seeing a flatfish, a sighting many scientists still doubt, before turning back. No one returned to the Challenger Deep for another 52 years.
In 1982, oceanographer Robert Ballard asked the U.S. Navy to fund the robotic technology he needed to find the Titanic. The Navy agreed on one condition: he first had to use it to investigate the wrecks of two lost nuclear submarines, USS Thresher and USS Scorpion, and keep that mission secret. The submarine work left him just 12 days. The wrecks had taught him that heavy debris sinks fast while lighter pieces scatter, so his team swept the seafloor for the Titanic's debris trail and found the wreck on September 1, 1985. Pieces of the secret leaked in the 1990s, but the Navy discussed it openly only in 2008.
On September 19, 1979, marine biologist Sylvia Earle rode to the seafloor off Oahu, Hawaii, strapped to the front of a small submersible and sealed inside an armored JIM suit. At 381 meters, about 1,250 feet down, she unhooked herself from the vehicle and explored the bottom on her own for more than two hours. It still stands as the Guinness World Record for the deepest untethered sea walk by a woman. Earle, nicknamed Her Deepness, had already led the first all-female team of aquanauts during the 1970 Tektite II project, living under the sea for two weeks.
At Columbia University's Lamont Geological Observatory, women were kept off research ships, and geologist Marie Tharp would not sail on one until 1968. So she spent the early 1950s at a desk, turning ships' sonar readings into profiles of the Atlantic seafloor. In 1952, she spotted a V-shaped notch running down the center of the undersea mountain range and concluded it was a rift valley where the seafloor was spreading apart. Her colleague Bruce Heezen first dismissed the idea as girl talk, and it took her between six months and a year to convince him. Their 1957 map of the North Atlantic helped clear the way for plate tectonics.
On March 26, 2012, film director James Cameron piloted the submersible Deepsea Challenger alone to the bottom of the Challenger Deep, reaching 10,908 meters and becoming the first person to make the trip solo. The descent took about two and a half hours. He then spent about three hours on the bottom, the first crewed scientific exploration of the site, filming with 3D cameras lit by a tower of LEDs. Not everything worked: a hydraulic leak disabled the sub's mechanical arm, so he brought back no biological samples. Cameron had co-designed the sub with Australian engineer Ron Allum.
An injury left naval officer Matthew Fontaine Maury unfit for sea duty, so he studied the sea from a desk instead. As superintendent of the U.S. Naval Observatory, he combed through thousands of ships' logs to chart the ocean's winds and currents, publishing his first Wind and Current Charts in 1847 and distributing them free to captains who agreed to share their own logbook data in return. The charts are credited with shortening the sailing route from New York to San Francisco by about 47 days. In 1855, Maury published The Physical Geography of the Sea, considered the first oceanography textbook, earning him the nickname Pathfinder of the Seas.
Between December 2018 and August 2019, retired naval officer and private equity investor Victor Vescovo became the first person to reach the deepest point of all five of Earth's oceans, an effort called the Five Deeps Expedition. Piloting Limiting Factor, a submersible he spent years developing with Triton Submarines, he dove to the Puerto Rico Trench in the Atlantic, the South Sandwich Trench in the Southern Ocean, the Java Trench in the Indian Ocean, the Challenger Deep in the Pacific, and finally the Molloy Deep in the Arctic. Scientists on the expedition collected samples throughout and turned up dozens of possible new species.
Australia's Great Barrier Reef stretches about 1,430 miles along the coast of Queensland and is made up of nearly 3,000 individual reefs. It was built by tiny coral polyps, which secrete calcium carbonate skeletons that cement their colonies together; over hundreds and thousands of years, the colonies join and become reefs. NOAA calls it the largest living structure on Earth, large enough to be seen from space. Reefs like it punch far above their size: coral reefs cover less than one percent of the ocean floor, yet they support about 25 percent of all marine creatures.
Every other sea on Earth is bordered by land, but the Sargasso Sea, in the middle of the North Atlantic, is bounded only by ocean currents. The Gulf Stream forms its western edge, the North Atlantic Current its northern edge, the Canary Current its eastern edge, and the North Atlantic Equatorial Current its southern edge, together forming a slow, clockwise gyre. The sea takes its name from sargassum, a floating brown seaweed that drifts and accumulates within this current-bound gyre rather than growing attached to any coastline, providing habitat for eels, sea turtles and fish that spend part of their lives far from land.
In 1768, Benjamin Franklin, then deputy postmaster general for the American colonies, was asked about a puzzling complaint: mail packets from England took about two weeks longer to reach New York than merchant ships took to reach Rhode Island. His cousin Timothy Folger, a Nantucket sea captain, explained that the Rhode Island captains knew the Gulf Stream and the packet captains did not, so the packets sailed straight against a current running about three miles an hour. Folger sketched its course, and in 1769 Franklin had it engraved as the first chart of the Gulf Stream. The packet captains, Franklin later wrote, slighted it.
Mosquito Bay, on the Puerto Rican island of Vieques, holds the Guinness World Record for the brightest bioluminescent bay, a title recognized in 2006. The glow comes from Pyrodinium bahamense, a microscopic dinoflagellate packed into the bay at up to 700,000 per gallon of water. Disturb the water, with a paddle stroke or a passing fish, and they flash blue-green light for about a tenth of a second. The bay's narrow mouth keeps the dinoflagellates from washing out to sea, and decaying mangroves supply plenty of food, which is why this bay outshines the other glowing bays on the same island.
Belize's Great Blue Hole is a nearly perfect circle of deep blue water, about 1,000 feet across and roughly 400 feet deep, sitting inside the pale shallows of Lighthouse Reef. It began as a dry limestone cave system during past ice ages, when sea levels were far lower. As the seas rose, the caverns flooded and their roofs collapsed, leaving a vertical cave in the reef. In 1971, Jacques Cousteau brought his ship Calypso to chart the hole, and his team retrieved stalactites from its submerged caves. Stalactites can form only on dry land, proof that the hole once stood above the sea.
The Bay of Fundy, between Nova Scotia and New Brunswick, has the largest tides on Earth. Near Wolfville, in Nova Scotia's Minas Basin, high water can stand as much as 53 feet, about 16 meters, above low tide, while the world's average tide moves sea level only about three feet. The cause is resonance: water in the funnel-shaped bay sloshes back and forth with a natural period of about 12 hours, nearly the same as the tidal cycle, and the match amplifies each tide. At the Hopewell Rocks, visitors walk the beach among rock formations at low tide that become islands when the water returns.
The name Southern Ocean had been used for the waters around Antarctica for decades: the International Hydrographic Organization recognized it in 1937, only to drop it in 1953. On June 8, 2021, World Oceans Day, National Geographic began labeling it on its maps as Earth's fifth ocean. What sets it apart is a current, not a coastline: the Antarctic Circumpolar Current, established roughly 34 million years ago when Antarctica separated from South America. Inside that ring the water is colder and slightly less salty than the ocean to the north, and its unique, fragile ecosystems are home to whales, penguins and seals.
8The tip of the iceberg is the smaller part, by far
On the tile: Iceberg
The saying about the tip of the iceberg is grounded in physics. Glacial ice is only slightly less dense than seawater, so about seven-eighths of an iceberg, more than 87 percent of its mass, floats below the waterline, according to the U.S. Coast Guard. Because bergs come in irregular shapes, some stand taller out of the water than others, but the share of their mass hidden underwater stays nearly the same, set by the densities of the ice and the sea. Whatever a lookout can see from a ship's deck is roughly an eighth of the berg; the rest lies hidden below.
Once a year on Australia's Great Barrier Reef, more than 130 species of coral take part in a mass spawning, releasing bundles of eggs and sperm into the water at night. The timing follows the full moon: spawning comes a few nights after it, once warming water has ripened the egg and sperm bundles, and scientists think the onset of darkness helps set the moment. Inshore reefs usually spawn in October, while outer reefs wait until November or December. Different species spawn on different nights to prevent cross-breeding, and fish and plankton feast on much of the spawn.