What's Really Hiding In The Deepest Oceans

TL;DR

The deep ocean harbors millions of undiscovered species, and environmental DNA sampling can now detect unknown life from just a drop of water.

Key Points

• 1.Colossal squid remain virtually unseen despite their massive size. Making up ~80% of a sperm whale's diet and growing over 9 meters long, a live colossal squid was only first filmed in 2025 — 100 years after we discovered the species existed.
• 2.The ocean's largest daily migration dwarfs anything on land. Every night, billions of tons of animals rise hundreds of meters from the deep to feed at the surface — more biomass moving than the great African migration — while also pulling carbon deep into the sea.
• 3.Deep-sea gigantism produces creatures up to 16x their normal size. Cold water (0–4°C) holds more oxygen and slows metabolism, enabling isopods to reach 40 cm, amphipods 30 cm, and potentially the colossal squid — a phenomenon called polar gigantism.
• 4.Filming a giant squid in its natural habitat required extraordinary effort. In 2012, scientists used red LEDs (invisible to deep-sea animals), silenced motors, and a blue bioluminescent lure at 700m depth — backed by 20 years of whale data and over 100 dives — for just a few minutes of footage.
• 5.Environmental DNA (eDNA) lets scientists detect ocean life from a single water sample. By filtering water for shed DNA — scales, mucus, feces — researchers can target specific species like the critically endangered angel shark or sweep broadly for hundreds of species at once without expensive submersibles.
• 6.90% of DNA found in abyssal ocean samples is completely unknown 'dark taxa.' Scientists estimate over 2 million marine species exist but fewer than 10% are documented; researchers are now using AI and machine learning to classify these unknown sequences and map ocean biodiversity at scale.