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Deep within the dark depths of the sea many marine animals are providing their own electricity.

In a new study conducted by the Monterey Bay Aquarium Research Institute, researchers Séverine Martini and Steve Haddock found that three quarters of the animals in Monterey Bay waters between the surface and 3,900 meters deep can produce their own light.

According to the researchers, it is difficult to get a true inventory of illuminated animals because very few cameras are sensitive enough to show the pale glow of many marine animals and below 300 meters the ocean is essentially pitch black, meaning animals do not need to glow very brightly.

“I'm not sure people realize how common bioluminescence is,” Martini said in a statement. “It's not just a few deep-sea fishes, like the angler fish. It's jellies, worms, squids...all sort of things.”

Most animals also don’t glow continuously because making light takes extra energy and can attract predators.

The research team compiled data on every animal larger than one centimeter that appeared in videos from 240 dives by MBARI’s remotely operated vehicles (ROVs) in and around Monterey Canyon.

The team counted more than 350,000 individual animals, each of which had been identified by MBARI video technicians using a database called the Video Annotation and Reference System (VARS), which contains over 5 million observations of deep-sea animals and has been used as a source of data for more than 360 research papers.

Martini compared the list of animals observed during the 240 ROV dives with a list of animals and animal groups previously known to be bioluminescent, which was based on a review of previous scientific papers and firsthand observations.

Martini divided the observed animals into five different categories based on the likelihood they are bioluminescent.

While the total number of glowing animals decreased with depth, the researchers attributed this to the fact that there are simply fewer animals of any kind in deeper water.

And while the percentage of glowing to non-glowing animals was similar at all depths, the researchers observed that different groups of animals were responsible for the light produced at different depths.

For example, from the sea surface to 1,500 meters deep, the majority of the glowing animals were jellyfish or comb jellies and from 1,500 meters to 2,250 meters’ deep worms were the most abundant glowing animals. Below that, small tadpole-like animals called larvaceans accounted for about half of the glowing animal population observed.

The findings also show that between 97 and 99.7 percent of cnidarians in the video produce their own light while only about half of the fishes and cephalopods are bioluminescent.

The next step is to develop instruments that can reliably measure the total bioluminescence from all animals at a given depth.

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