An ecosystem in perpetual night
Krubera Cave, in the Arabika Massif of the Western Caucasus mountains, is the second-deepest known cave on Earth. Ukrainian diver Gennady Samokhin set its current maximum depth record of 2,199 meters (7,215 feet) in 2012. For years it was considered the world's deepest, but it is now ranked second to the nearby Veryovkina Cave. Krubera is one of only two caves known to be deeper than 2,000 meters.
The cave is a network of deep pits and narrow passages carved through Upper Jurassic and Lower Cretaceous limestone. Beyond the entrance zone, no sunlight penetrates, creating a completely dark environment with near-total humidity and stable, cold temperatures between 2 and 4 degrees Celsius.
Life in these deep zones is completely dependent on allochthonous organic material—nutrients that wash down from the surface. Water percolating through the rock carries dissolved organic matter, fungi, and microbes, which form the base of the food web. This sparse nutrient supply supports a community of highly adapted organisms.
The inhabitants of the abyss
The deep zones of Krubera Cave host a unique biological community of more than 12 species of arthropods. Many of these are troglobites, animals that are physiologically adapted to life in permanent darkness. Typical adaptations include a lack of eyes, no pigmentation, and better non-visual senses. The cave's fauna includes species of pseudoscorpions, spiders, crustaceans, beetles, and dipterans.
During a 2010 expedition, researchers made a remarkable discovery. At a depth of 1,980 meters (6,500 feet), they found a species of springtail named Plutomurus ortobalaganensis. This arthropod holds the record for the deepest-living terrestrial animal ever found. It survives by feeding on fungi and decaying organic matter in the lightless, near-freezing environment.
Three other new species of springtail were also discovered during that expedition: Anurida stereoodorata, Deuteraphorura kruberaensis, and Schaefferia profundissima. These animals demonstrate that life can persist far deeper into the Earth's crust than previously thought, subsisting on the planet's most limited energy budgets.