Researchers discovered a thriving ecosystem in the Saudi Arabian Red Sea.

Shannon Klein and her team probed two deep-sea zones during the 2022 Red Sea Decade Expedition, revealing a hidden world beneath the vibrant coral reef.

They uncovered unexpected fish lurking in the shadowy, oxygen-starved depths of the sea.

Using remotely operated vehicles and crewed submersibles, the researchers dived into the Amq Deep, plunging 619 m (2,031 ft) below the surface. They spotted lace corals and a trio of fish species—lightfish, soldierfish, and vast schools of lanternfish. This group of lanternfish, dawdling at a pace five times slower than their cousins in oxygen-rich waters, may sneak upward at night to gulp air and snatch a meal.

The Farasan Deep, a 491-metre (1,611-ft) plunge where near-anoxic conditions below 2 micromoles of oxygen per kilogram should spell doom for air-breathing creatures. However, unidentified fish were caught gliding along the sediment's surface. Persistent low-oxygen zones like these are familiar in temperate seas, but the tropics have kept their secrets—until now.

The researchers said: 'The warm and saline environment of the Red Sea interacts with deep enclosed depressions to restrict vertical mixing, limiting oxygen resupply at depth—and similar zones are likely to occur in abundance in other tropical coastal areas, perhaps with their own adapted fauna.'

The Red Sea's warm, salty embrace and deep, enclosed pockets stifle oxygen flow, crafting these strange habitats. Experts reckon similar spots dot tropical coasts worldwide, each potentially hiding its own quirky cast of underwater survivors.