April 10 (UPI) -- There a few ecosystems on Earth where the sun doesn't shine. The largest is the deep sea. Below 1,000 feet, the ocean is pitch black.
According to new research, the vast majority of creatures found at such depths create their own light.
Researchers from the Monterey Bay Aquarium Research Institute analyzed the footage from 240 dives conducted by the institute's remote-controlled submersibles. The survey identified more than 350,000 individual animals using the Video Annotation and Reference System.
Scientists compared the results of their survey with a database of species known to be bioluminescent and classified the identified individuals into one of five categories: definitely bioluminescent, highly likely to be bioluminescent, very unlikely to be bioluminescent, definitely not bioluminescent and undefined.
The research showed nearly three-quarters of all deep-sea dwellers produce their own light. Surprisingly, scientists say, the percentage of bioluminescent species is consistent at a range of depths. However, the groups of animals responsible for bioluminescence at each depth changes.
Between the surface and roughly 5,000 feet, bioluminescence is mostly produced by jellyfish and comb jellies. Between 5,000 and 10,000 feet, most bioluminescent creatures are marine worm species. Most of the glowing species below 10,000 feet are small sperm-like filter feeders called appendicularians, or larvaceans.
"I'm not sure people realize how common bioluminescence is," MBARI researcher Severine Martini said in a news release. "It's not just a few deep-sea fishes, like the angler fish. It's jellies, worms, squids...all sort of things."
Study authors Martini and Steve Haddock published their work in the journal Scientific Reports.