Ocean: quotes, facts and reflections

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WonderScience

A dead whale that sinks to the deep seafloor can feed a succession of animals and microbes for decades, becoming a rich island of food where food is scarce.

Scientists call such a carcass a 'whale fall', and it is used up in stages. First, scavengers such as sleeper sharks strip most of the soft tissue over a period of months to about two years. Next, worms, crustaceans and other small animals colonise the bones and the surrounding mud, which the remains have enriched. In the longest stage, which can last decades, bacteria break down the fats inside the bones and release hydrogen sulphide; other bacteria draw energy from this chemical, and mussels and clams that carry such bacteria inside them live on it, in a food chain that does not depend on sunlight. Bone-eating Osedax worms, discovered on a whale fall off California in 2002, bore into the bones with the help of bacteria that digest them.

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StillnessScience

Kelp forests grow in cool coastal seas from giant brown algae, not plants, and shelter a great variety of fish, invertebrates, seals and sea otters.

Kelp are large brown algae. Instead of roots they have a grip-like base called a holdfast, and gas-filled bulbs hold their fronds up towards the light. Giant kelp can grow up to about 60 centimetres a day and reach more than 30 metres, forming a canopy at the surface like the treetops of a forest. Kelp forests grow along cool coasts from California and Chile to South Africa, Australia and Norway. In the North Pacific, sea otters help protect them by eating sea urchins, which graze on kelp. Where otters were hunted out for their fur, urchins multiplied and stripped forests down to bare rock, leaving what are called urchin barrens.

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WonderScience

Corals are tiny reef-building animals; on some nights, whole colonies release eggs and sperm into the sea at once.

Scientists call this mass spawning. On Australia's Great Barrier Reef it usually happens between October and December, a few nights after a full moon, once the water has warmed; the release starts after dark, and many species spawn within the same short window. Divers describe the water filling with drifting pink and orange bundles, like snow falling upwards. Releasing everything at once gives predators far more eggs than they can eat, and raises the chance that eggs and sperm from different colonies meet. Fertilised eggs become larvae that drift for days or weeks before settling on the reef to start new corals. Researchers are now studying whether warming seas are disrupting this timing.

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WonderOcean

In March 2025, researchers filmed a live colossal squid in its natural deep-sea habitat for the first time: a transparent juvenile about 30 cm long.

Schmidt Ocean Institute's remotely operated vehicle SuBastian recorded the juvenile at about 600 m depth near the South Sandwich Islands in the South Atlantic on 9 March 2025, a hundred years after the species was first described. The colossal squid (Mesonychoteuthis hamiltoni) is a different species from the better-known giant squid: shorter, but much heavier. The largest specimen ever weighed, caught in the Ross Sea in 2007, was 495 kilograms, making it the heaviest known invertebrate, and its eyes, about 27 cm across, are the largest measured in any animal. Until 2025 the species was known only from remains in the stomachs of whales and seabirds and from dying adults hauled up by fishing boats.

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WonderOcean

When a giant iceberg broke away from Antarctica in 2025, scientists rushed in and filmed a thriving world of life on the seafloor that had been sealed under ice for centuries.

The iceberg, called A-84, broke off the George VI Ice Shelf on the Antarctic Peninsula in January 2025. It covered about 510 square km, roughly the size of Chicago, and uncovered seabed that had been roofed by floating ice for centuries. Soon after, the Schmidt Ocean Institute's research ship Falkor (too) arrived and sent down its underwater robot SuBastian. It found large corals and sponges, icefish, giant sea spiders, octopuses and a ghostly phantom jellyfish. Some animals were so big that they must have been growing there for decades, perhaps centuries, which surprised scientists who had expected little life without sunlight. Ocean currents probably carry food in under the ice.

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WonderOcean

Rig sharks, small sharks from New Zealand waters, make sharp clicking sounds when they are handled. Recorded in 2025, it was the first documented case of a shark producing sound on its own.

Many bony fish grunt or drum using their swim bladder, a gas-filled sac that sharks do not have, so sharks were long assumed to be silent. A team led by marine biologist Carolin Nieder, working at the University of Auckland, recorded young rig sharks in tanks and found that they clicked when gently held. The clicks seem to come from the shark snapping its flat, overlapping teeth together rather than from a special sound-making organ. What they are for is still unknown; one idea is that they are a startle response to being grabbed. The findings were published in the journal Royal Society Open Science in March 2025, and researchers now want to know whether other sharks make sounds too.

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WonderOcean

In 1872 the American merchant ship Mary Celeste was found drifting in the Atlantic in good order, with its cargo intact, food in the galley and the crew's belongings untouched. The ten people aboard were never seen again.

The Canadian brigantine Dei Gratia came upon the ship off the Azores on 4 December 1872, a month after it had left New York for Genoa with 1,701 barrels of industrial alcohol. Its only lifeboat was gone and the last log entry was ten days old, which suggests the people aboard left in a hurry but in order. Captain Benjamin Briggs had his wife and two-year-old daughter with him. A makeshift sounding rod, used to measure water in the hold, lay on deck, and one early theory is that a false reading made Briggs think the ship was sinking fast. Another is fear of fumes from the alcohol. Arthur Conan Doyle's 1884 short story, which invented many details, did much to turn the case into a legend.

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WonderMigration

Polynesian navigators crossed thousands of kilometres of open Pacific without compass, charts or instruments. They steered by rising and setting stars, the sun, ocean swells and seabirds, and kept track of speed and direction in their heads.

By the 1970s the old skills had almost disappeared, and some scholars argued that the Pacific islands had been settled by canoes drifting there by chance. The Polynesian Voyaging Society set out to test this with the help of Mau Piailug, a master navigator from the small island of Satawal in Micronesia, where a closely related tradition survived. In 1976 he guided the double-hulled canoe Hōkūleʻa about 4,000 kilometres from Hawaii to Tahiti without any instruments. The voyage showed that deliberate long-distance navigation was possible. Piailug went on to teach Hawaiian navigators, among them Nainoa Thompson, and traditional wayfinding has since been revived across the Pacific.

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WonderCulture

The haenyeo of Jeju, an island off South Korea's southern coast, are women who dive without breathing equipment, holding their breath for one to three minutes to gather abalone, sea urchins, octopus and seaweed from as deep as 20 metres.

Haenyeo means 'sea women' in Korean. Girls traditionally learned the work from older divers in their village, and the women run local diving associations that set rules on when and what may be harvested and look after one another's safety. UNESCO recognised this way of caring for the sea when it added the culture of Jeju haenyeo to its Intangible Cultural Heritage list in 2016. Their numbers have fallen sharply, from 23,081 in 1965 to 14,143 by 1970 and a few thousand today. Most are now over 60, and some of the oldest, past 80, still dive.

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WonderOcean

Coral reefs cover less than 1 per cent of the ocean floor, yet they support about a quarter of all known marine species. They also shield coasts from storm waves.

A reef is built by coral polyps, tiny animals related to jellyfish that lay down skeletons of limestone. Most reef corals carry single-celled algae inside their tissue; the algae photosynthesise and pass food to the coral in return for shelter, and they also give it its colour. When the water stays too warm for too long, corals expel the algae and turn white, which is called bleaching; if the heat lasts, they starve and die. A global bleaching event from 2014 to 2017 hit about two-thirds of the world's reefs, and a fourth, from 2023 to 2025, the most severe on record, reached about 84 per cent of reef area.

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StillnessOcean

Mangroves, salt marshes and seagrass meadows draw carbon dioxide from the air and lock it away in waterlogged coastal mud, often for centuries. Scientists call this stored carbon 'blue carbon'.

The term was popularised by a 2009 United Nations report. Coastal mud holds so little oxygen that dead roots and leaves rot very slowly, so carbon keeps building up in the soil instead of returning to the air. These habitats cover only a small fraction of the seabed, yet they are thought to account for about half of all the carbon buried in ocean sediments. Mangroves also break waves, trap sediment and shelter young fish and crabs among their roots. When the wetlands are drained or cleared for shrimp farms or building, the stored carbon can escape back into the atmosphere.

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WonderOcean

Hydrothermal vents, hot springs on the deep ocean floor, support dense communities of animals in total darkness. Their food chain starts not with sunlight but with microbes that make food from chemicals in the vent water, a process called chemosynthesis.

In February 1977 the geologist Jack Corliss and colleagues took the submersible Alvin down about 2,500 metres to the Galápagos Rift, a crack in the Pacific seafloor, expecting bare rock. Instead they found warm vents ringed with clams, mussels, crabs and tube worms. Vent water is rich in hydrogen sulphide, a gas poisonous to most life, but some bacteria can draw energy from it to build sugars, much as plants use sunlight. Giant tube worms, which have no mouth or gut, house these bacteria inside their bodies and live on what they make. The find changed ideas about where life can exist, on Earth and possibly beyond it.

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WonderMigration

European eels live in the rivers of Europe and North Africa but begin life some 5,000 kilometres away in the Sargasso Sea, in the western Atlantic. Adults swim back there to breed, yet no one has ever seen them spawn.

How eels breed puzzled people for more than 2,000 years; Aristotle thought they arose from mud. In the early 1900s the Danish biologist Johannes Schmidt spent almost two decades netting eel larvae across the Atlantic and found that they grew smaller the further west he went, until the tiniest turned up only in the Sargasso Sea. The larvae drift to Europe with the Gulf Stream and turn into transparent 'glass eels' as they near the coast. In 2022 researchers reported the first direct evidence of adults reaching the Sargasso Sea, after tracking satellite-tagged eels released in the Azores. No eggs or spawning adults have yet been found. The species is now critically endangered.

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WonderEvolution

In the Cambrian explosion, which began about 538 million years ago, most of the major animal groups alive today appeared in the seas within roughly 20 million years, among them the first arthropods, molluscs and early relatives of vertebrates.

The name makes it sound sudden, but the Cambrian explosion unfolded over millions of years and built on the simpler life of the preceding Ediacaran period. What changed was the sheer variety: eyes, legs, shells and hard skeletons appear, along with burrows and the first clear signs of predators hunting prey. Two exceptional fossil beds preserve even soft tissue: Chengjiang in China, about 518 million years old, and the Burgess Shale in Canada, about 508 million years old. Trilobites, armoured sea-floor arthropods, appear early in the period and survived for some 270 million years. Leading explanations for the burst include rising oxygen in the oceans, new genetic tools for building bodies, and an arms race between predators and prey.

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WonderTrade

For more than two thousand years, Indian Ocean trade ran on the monsoon winds, which reverse with the seasons. Timing their voyages to them, merchants linked East Africa, Arabia, India, South-East Asia and China through a chain of busy ports.

In the northern Indian Ocean the monsoon blows from the south-west in summer and from the north-east in winter, so a ship could sail out on one season's wind and home on the next. A Greek sailing guide from the first century AD, the Periplus of the Erythraean Sea, already describes this trade between Egypt, Arabia, East Africa and India. Arab and Persian dhows (wooden sailing ships), Indian and Malay vessels, and later Chinese fleets used the same system; Admiral Zheng He's expeditions reached East Africa in the early 1400s. Ports such as Kilwa, Calicut and Malacca grew rich on spices, cotton cloth, porcelain and gold, and Islam, Swahili culture and many words travelled the same routes.

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WonderTrade

From 1565 to 1815, Spanish ships known as the Manila galleons crossed the Pacific between Manila in the Philippines and Acapulco in Mexico, carrying Asian silk, porcelain and spices east and returning with American silver.

Usually only one or two galleons sailed each way a year. The westward run from Acapulco took about three months on the trade winds, but the return had to swing far north to catch westerly winds and could take four to six months, and scurvy and storms cost many lives. Much of the silver, mined at Potosí in today's Bolivia and at Zacatecas in Mexico, ended up in China, whose economy increasingly ran on silver. Chinese porcelain arriving in Mexico influenced the blue-and-white Talavera pottery of Puebla, and Manila grew into a meeting place for Chinese, Spanish, Filipino and Japanese traders. Dozens of galleons were wrecked over the route's 250 years.

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WonderTrade

Cowrie shells, the glossy shells of small sea snails, served as money in parts of Africa, Asia and the Pacific for centuries, because they were durable, easy to count and carry, and hard to fake.

Cowries were used in China during the Shang dynasty, more than 3,000 years ago, and the Chinese sign for 'shell' still appears inside many characters to do with money, such as those for 'goods' and 'buy'. Most of the cowries used in Asia and Africa came from the Maldive Islands. The traveller Ibn Battuta saw them used as currency in the Mali Empire in the 1350s, and from the sixteenth century European ships carried them to West Africa by the ton, often as ballast. There they paid for everyday goods and taxes, and they were also used to buy enslaved people in the Atlantic slave trade. As imports soared their value fell, and colonial currencies replaced them around 1900.

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WonderOcean

Whales feed at depth and release nutrient-rich faeces near the surface, fertilising the phytoplankton, tiny drifting algae, at the base of the ocean food chain. Scientists call this the whale pump.

The term comes from a 2010 study by the marine scientists Joe Roman and James McCarthy, who looked at whales and seals in the Gulf of Maine, off the north-eastern United States. Many whales dive to feed and then rest and breathe at the surface, where they release loose, floating plumes of faeces rich in nitrogen. The researchers estimated that marine mammals return about 23,000 tonnes of nitrogen a year to the sunlit surface layer of the Gulf, more than all the rivers flowing into it combined, and that before industrial whaling the flow was probably much larger. Other studies found a similar effect with iron in the Southern Ocean. Because phytoplankton also absorb carbon dioxide, recovering whale numbers may help both ocean productivity and carbon uptake.

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WonderMigration

Starting from Taiwan more than 4,000 years ago, seafarers speaking languages of the Austronesian family settled the islands of South-East Asia and much of the Pacific, as far as Hawaii, New Zealand and Easter Island, and to the west reached Madagascar.

Most linguists, archaeologists and geneticists agree that the expansion started in Taiwan and reached the Philippines by around 2000 BC, though the newcomers mixed extensively with people already living in the islands. Sailing outrigger canoes, boats steadied by a float on one side, they carried taro, yams, pigs, dogs and chickens. From about 3,300 years ago a distinctive stamped pottery called Lapita marks their spread into the western Pacific. Navigating by stars, ocean swells and birds, Polynesian voyagers later reached Hawaii, Easter Island and finally New Zealand, around AD 1250 to 1300. About 1,500 years ago others crossed the Indian Ocean to Madagascar, which is why Malagasy is most closely related to a language of Borneo.

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WonderMigration

The sardine run takes place off South Africa's east coast from about May to July, when vast shoals of sardines follow a band of cool water north along the shore. Dolphins, gannets, sharks, seals and whales gather to feed on them.

Sardines normally live in the cooler waters off South Africa's southern and western coasts. In some winters a narrow strip of cold water forms close to the shore of the Eastern Cape and KwaZulu-Natal, between the coast and the warm Agulhas Current, and the fish move north along it. The shoals can stretch for several kilometres and are followed from the air by spotter planes. Common dolphins herd the sardines into tight balls near the surface, Cape gannets plunge in from height, and sharks, Cape fur seals and Bryde's whales feed on the exposed fish. Scientists are still not sure what sets the run off: in some years it is weak or barely happens, and why is not fully understood.

KwaZulu-Natal sardine runRead card

DriveTrade

The Suez Canal in Egypt, opened in 1869, links the Mediterranean to the Red Sea, so ships between Europe and Asia no longer have to sail around Africa. Dug partly by forced labour and later fought over by empires, it still carries a large share of world trade.

The French diplomat Ferdinand de Lesseps led the company that dug the canal. In its early years tens of thousands of Egyptian peasants were made to work on it under the corvée, a system of compulsory unpaid labour, until the practice was stopped in 1864. Egypt's debts later forced it to sell its 44 per cent stake to Britain in 1875, and British troops stayed in the canal zone until 1956. That year President Gamal Abdel Nasser nationalised the canal, and Britain, France and Israel invaded. International pressure, above all from the United States, forced them to withdraw, a turning point in the end of European empire in the Middle East. In March 2021 the container ship Ever Given ran aground and blocked the canal for six days.

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WonderNature

Great frigatebirds can sleep while soaring over the ocean, sometimes with one half of the brain and sometimes with both. In flight, though, they sleep only about 40 minutes a day, against more than 12 hours a day on land.

The finding comes from a 2016 study led by Niels Rattenborg of the Max Planck Institute for Ornithology in Germany. His team fitted great frigatebirds nesting in the Galápagos Islands with small devices that recorded brain activity during flights lasting up to ten days. Most sleep came in bursts of about twelve seconds, often while the birds circled upward in rising warm air. When only one half of the brain slept, the eye linked to the awake half usually looked in the direction of flight. Frigatebirds hunt far out at sea, yet their feathers are not waterproof, so they cannot rest on the water. How they cope with so little sleep is still not known.

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WonderOcean

Some sea slugs keep the chloroplasts of the algae they eat, the tiny green parts that turn sunlight into food, working inside their own bodies. The stolen chloroplasts can go on photosynthesising for days or, in some species, months.

These slugs belong to a group called the Sacoglossa, and the habit is known as kleptoplasty, from the Greek for 'thief' and 'formed'. They pierce algal cells, suck out the contents and store the chloroplasts in cells lining the gut. The best-known example, the emerald green Elysia chlorotica of North America's Atlantic coast, can keep chloroplasts from the alga Vaucheria litorea working for months. Scientists once thought the slug had taken algal genes into its own DNA to maintain them, but later genetic studies did not confirm this, and how the chloroplasts last so long is still debated. So is how much they feed the slug: in some experiments, starved slugs kept in the dark survived about as long as those kept in light.

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WonderOcean

Every night, vast numbers of sea animals rise from the depths towards the surface to feed, then sink back before dawn. This daily journey, called diel vertical migration, carries carbon down into the deep ocean.

The migration was first noticed by accident. In 1942 the scientists C. F. Eyring, R. J. Christensen and R. W. Raitt, working with sonar aboard the USS Jasper, found a false seafloor 300 to 500 metres down by day that sat shallower at night. The echo came from millions of animals, above all small fish of the dim middle depths whose gas-filled swim bladders reflect sound. The layer is now called the deep scattering layer. The animals rise under cover of darkness to feed on plankton and descend at dawn to hide from predators that hunt by sight. By mass it is often described as the largest migration on Earth, and it moves carbon downwards as the animals breathe, excrete and are eaten at depth.

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