City Without Sunlight: Deep Sea Life, Glass Skeletons and Science at Loki's Castle

On 17 February 1977, off Ecuador, 330 kilometres from the Galapagos Rift, the small white submersible Alvin slipped into the Pacific. Inside were a pilot and two geologists hunting for hot-water sources — hydrothermal vents. Textbooks at the time agreed on one rule: without sunlight no food chain can start. Two days earlier a 2-ton steel sled named Angus (a towed camera platform with strong lights) had sensed hot water at 2.5 kilometres depth. As Alvin approached the vent, the window showed not theory but a crowded city — white clams about a foot long and red-capped tube worms sprouting from rock. In minutes the crew understood this was no barren plain. That day biology opened a new door: life does not need the sun.

By deep sea we mean below 200 metres. Light fades around 200 metres and by 1,000 metres it is total darkness. The scale is startling: 98.5% of Earth's living volume is in this dark zone. Forests, grasslands and rivers together make only 1.5%. Yet as of April 2026 only 28% of the ocean floor is mapped to modern standards; more than 70% remains poorly known. We have sharper maps of the Moon and Mars than of our own seabed. A May 2025 analysis in Science Advances gathered 43,681 dives since 1958 (every submersible, ROV and camera record) and calculated that humans have directly seen just 0.001% of the deep floor. How do we protect a world we have barely seen?

Life here must solve three problems: pressure, darkness and hunger. The Mariana Trench's Challenger Deep tells the story best — about 10,900 metres deep. Turn Everest upside down into it and 2 kilometres remain between summit and bottom. There, load on every square inch is about 7,300 kilograms, like 100 elephants on your head. Human lungs (air-filled) and sinuses would be crushed. Why are deep animals not crushed? Simple physics: crushing needs air, gas or empty space. Most deep creatures are almost entirely water (water-based bodies) and water does not compress; they have neither lungs nor gas bladders. Like a water-filled balloon that keeps its shape at depth, they balance pressure from within.

In 1979 scientists returned to the same Galapagos ground, this time with biologists and a breakthrough television camera that filmed never-before-seen motion pictures in the black abyss. They found giant tube worms up to 2 metres long. No mouth, no gut — how do they eat? Inside the body lies the trophosome (a bacteria-packed organ) that answers it. Worms take hydrogen sulphide (toxic for most animals) and oxygen from vent fluids and carry them via blood to bacteria. Bacteria make energy from the chemical, and that energy feeds the worm. The process is chemosynthesis (chemical food production without sunlight). Think of it in four steps: 1) collect sulphide plus oxygen, 2) deliver to bacteria, 3) convert to chemical energy, 4) grow. It works so well the worms can grow 80 centimetres a year, the fastest growth among marine invertebrates.

Not every animal lives by a vent. On the open abyssal plain food arrives as marine snow — dead plankton, fish waste and organic bits that drift down like snowflakes. Most is lost on the way; only 0.5% to 2% of surface production reaches the bottom. The deep sea is Earth's most food-starved kitchen. Scarcity drives two odd outcomes. One is gigantism (deep-sea gigantism — same family grows far larger than shallow relatives). Example: the giant isopod Bathynomus, up to 20 inches, cat-sized. The other is extreme slowness. Both are two sides of the same equation: coping with rare and patchy food.

The most dramatic demo is a giant isopod caught off Mexico in 2007 and kept at Japan's Toba Aquarium. After eating normally, on 2 January 2009 it took a small fish piece and then stopped. Keepers tried fresh fish and varied diets; it ignored them. One year passed, then two, then five — it kept walking the tank and became a small celebrity in Japan. When it died on 14 February 2014 it had gone 1,868 days without a meal. Dissection found no obvious cause. How did it last? A June 2026 Cell study by the Chinese Academy of Sciences gave a two-part answer: 1) the stomach stretches like a warehouse and holds food for months, 2) metabolism is very low and energy management in the cold is ultra-efficient. The team also found an ancient energy gene ND1 that arrived by horizontal transfer from microbes, then duplicated and became ultra-expressed; in zebrafish it boosted starvation survival by 37%. Gigantism demands energy, but the same system solves famine — the paradox resolved.

The flip side of famine is a windfall: when a large whale dies. For the deep sea this is like thousands of years of marine snow arriving at once — a lottery win. First scavengers like hagfish and deep sharks strip soft tissue over months or years. Then bacteria take the bones, break down fats and release sulphide. That sulphide builds a mini vent-like ecosystem. In 2002 a whale skeleton in Monterey Canyon revealed a new animal: Osedax (bone worm — "bone-eating"). No mouth, no stomach; it roots into bone and with symbiotic bacteria digests fats and oils. The reproductive twist stunned biologists: at first only females were found. Where were males? Inside females. Microscopic dwarfs — more than 600 can live in one female's gelatinous tube — they do not feed or grow, their only job is to release sperm. A single whale fall can feed this system for up to 100 years, as a 2022 study estimated.

The deep sea's most famous face, the anglerfish (remember Finding Nemo's toothed fish with a glowing head bulb), takes reproduction even further. The bulb is the esca, packed with light-making bacteria Photobacterium. Fish gives bacteria housing and food, gets a dark-water lure to attract prey. Males have no esca and finding a female across thousands of kilometres of total darkness is statistically near impossible. Evolution found a bizarre fix: when a male finds a female he bites and never lets go. The tiny male fuses completely to the much larger female — mouth parts recede, blood systems join. He loses eyes and most organs, receives nutrients from her and gives only sperm. This fusion is unique among vertebrates and defies a 500-million-year-old adaptive immune system that normally rejects foreign tissue, as with human organ transplants. Work published in 2020 in Science and Nature Reviews Immunology showed anglerfish have lost key immune genes (especially the a3/a4 antibody diversity family), so the female does not reject the male because she has lost the system to do so.

Cold water also slows time. In April 2007 a submersible at 1,400 metres spotted an octmodel on a rock over its eggs. Thirty-eight days later the same animal was still there. Over the next 4.5 years scientists returned 18 times; each time the same sight — fading skin, dull eyes, no feeding. Fifty-three months later, in October 2011, the eggs had hatched and the mother was gone. It is the longest known egg-brooding period for any animal — cold slows embryo development and maternal metabolism alike. A champion of slowness is the Greenland shark (a slow, nearly blind shark of the North Atlantic and Arctic). It swims slower than a walking person, at a crawling baby's pace. In 2016 biologist Julius Nielsen dated eye lenses from 28 females (the central lens forms at birth and never changes) with radiocarbon dating. The largest was 392 years old, plus or minus 120 — potentially 500 years; it reaches maturity only at 150. The oldest shark alive today may have been born when Aurangzeb ruled India and become ready for pups around 1857.

How much of this strange life have we seen? Disturbingly little. In May 2025 Science Advances gathered 43,681 dives and estimated humans have observed only 0.001% of the deep seafloor directly. Mapping tells a similar story: about 72% remains unmapped to modern standards. That is why Norway's 2024 decision to open large Arctic waters to deep-sea mining triggered alarm; the plan Rathee had previously covered and petitioned with hundreds of thousands of signatures was halted at least until 2029 after protest. The most striking point: the area slated for mining had not even been properly observed. Greenpeace launched the Deep Arctic Expedition to fill the gap, bringing top researchers from Sweden, Spain, Norway and Germany.

The stage was off Norway at Loki's Castle (a ridge rich in hydrothermal vents). The original plan was to sail on Greenpeace's ship Witness, but Norwegian authorities denied permission and the team chartered a boat; water depth hit 15 metres almost immediately, with tight safety rules (hooked life jackets, overalls, helmets). On the larger research vessel they met ROV Holly — a vehicle that dives to 3 kilometres, pressure-tested, with two robotic arms and an ultra-high-definition camera. Holly is not driven but flown — it hovers just above the seabed to avoid harming life — and needs three pilots. Its winch, control room with three stations and more than 100 hours of video were ready. On deck Rathee held glass-skeleton sponges with gloves — bare hands would hurt from glass spines.

Sponges were the cruise's secret heroes. Deep-sea sponges are the only animal group on Earth that builds a glass skeleton; humans need high heat to make glass, sponges do it naturally. For sponge scientist Dr. Paco Cardenas the real superpower is elsewhere: sponges filter water continuously and trap DNA fragments of surrounding life. One sponge becomes a natural eDNA recorder for its area. Species never seen by cameras can be detected from sponge DNA traces. Tiny crustaceans taken from inside sponges looked like aliens under the microscope. Their symbiosis is also unique: while bacteria in humans are mostly in the gut, in sponges they live between cells and even inside cell nuclei — a total symbiosis where neither is complete without the other. That makes sponges priceless for understanding biodiversity.

The most symbolic moment came at 2,300 metres: Holly opened its arms and unfurled a banner reading "Listen to the Science!" It entered the record as the deepest banner protest in history, at a depth equal to about 130 five-storey buildings stacked, as Mongabay reported on 28 May 2026. Back on the ship, videographers watched hours of footage and cut highlights — shrimp swarms, spaceship-like jellyfish, white squid wrestling fish. Data and video are now in labs for analysis; new species are expected in coming months. Greenpeace's two aims are clear: stop deep-sea mining for good and create protected areas at sea. As Rathee puts it in the video, we often talk about saving forests and rivers we can see, but will we save a world we have not yet properly seen — or lose it without ever discovering it?