Lights of the deep sea

On her tenth birthday, Lina went deeper than anyone else in her class: a thousand metres below the surface of the ocean. She sat next to her Aunt Maya, a marine biologist, inside the Bubble, a small round submarine just big enough for two, with a porthole as thick as a dictionary.

At first the water was a bright blue. Then, as they sank, the blue grew darker. "Sunlight doesn't travel very far through water," Aunt Maya explained. "By a thousand metres there's none left at all. Down here it's always night." Lina pressed her forehead to the porthole. In the beam of the lights, white specks drifted slowly down. "Snow?" "It's called marine snow. Tiny bits of stuff sinking from the surface. Lots of animals down here eat it."

Lina was a bit disappointed. She had expected monsters, colours, something. There was only black water and that slow snow. Aunt Maya smiled. "Want to see who really lives here? Then we have to turn the lights off." She switched off the floodlights. The dark became so thick that Lina couldn't see her own hands.

Then a blue spark drifted past the porthole. Then another. Soon there were dozens, blinking, rippling, lighting up one after another. "Most of the animals that live here make their own light," Aunt Maya murmured. "It's called bioluminescence. It's often blue, because blue is the colour that travels furthest in water."

A jellyfish went by, spinning rings of light around itself like a carousel. "That's an Atolla. When a predator grabs it, it lights up like an alarm, to attract a bigger animal that will scare the attacker away." A little further off, a lanternfish crossed the dark with rows of glowing dots along its belly. Then Lina spotted a small light bobbing all on its own at the end of a kind of fishing rod. "An anglerfish," said Aunt Maya. "It wiggles its light, and curious little fish come closer."

Lina was quiet for a long time. She had thought the deep sea was empty, and it was full of signals, of little lamps that nobody ever saw. "They're not lighting up for us, are they?" "No. It's to find each other, or hide, or eat. We're just lucky to be here tonight."

The trip back up took more than an hour. Aunt Maya had turned on a small red night light in the cabin, and the motors hummed steadily. Wrapped in a blanket, Lina watched the black water turn midnight blue, then navy. She thought about the jellyfish spinning like a carousel. Long before they reached the surface, she was asleep, her cheek against the cool glass.