Year 7 NAPLAN Reading Prep — Set 2

Light in the Deep

More than a kilometre beneath the ocean's surface, sunlight vanishes entirely. In this permanent twilight zone, an astonishing survival strategy has evolved: producing light from living tissue. Scientists call this phenomenon bioluminescence, and it is far more common than most people realise. An estimated 76 per cent of deep-sea creatures — from anglerfish to jellyfish to tiny plankton — can generate their own glow.

The chemistry behind this glow is remarkably consistent across species. A molecule called luciferin reacts with oxygen, catalysed by an enzyme called luciferase, releasing energy as light rather than heat. This efficiency is extraordinary: while an incandescent light bulb wastes around 90 per cent of its energy as heat, a firefly or anglerfish converts nearly all of its chemical energy into visible light.

Deep-sea creatures have adapted this ability for wildly different purposes. The anglerfish dangles a luminous lure above its jaws, tempting curious prey close enough to strike. Some squid eject clouds of glowing ink instead of the usual black variety, momentarily blinding predators while the squid escapes into the darkness. Perhaps strangest of all is the cookiecutter shark, which uses a glowing underside to disguise its silhouette from creatures lurking below — a trick marine biologists call counter-illumination.

For decades, bioluminescence was considered a curiosity, of interest mainly to biologists and documentary filmmakers. That view is changing rapidly. Researchers have adapted luciferase into a laboratory tool used to detect contamination in food and water, and to track how genes switch on and off inside living cells. A discovery once dismissed as an oceanic oddity is now helping scientists monitor diseases and test the safety of drinking water.

The deep sea remains one of the least explored regions on Earth — humans have mapped more of the surface of Mars than the ocean floor. Every research voyage into these depths uncovers new species and new ways that light is used to hunt, hide and communicate. What other secrets might still be glowing, unseen, in the dark?