When stimulated, this sea cucumber (Pannychia moseleyi) produces a frenzy of bioluminescent light.

Advances in video cameras and low-light sensors are revealing animal behaviours in the deep sea that researchers have never recorded before.

The behaviours include a worm-like predator shooting off rings of blue light, and an animal anchored to the sea floor sending flashes of light dancing along its body, creating the illusion of a tiny creature swimming upwards.

Steven Haddock, a marine biologist at the Monterey Bay Aquarium Research Institute (MBARI) in California, will showcase videos of these phenomena and more for the first time on 13 September at the Deep Sea Biology Symposium in Monterey. He is one of a handful of researchers around the world who are using extremely high-resolution cameras and ultra-sensitive sensors to capture unprecedented footage of marine organisms in the wild.

“We can see natural behaviour in a way that we’ve never been able to before,” says Haddock.

This animal, called a sea pen (Halipteris californica), produces a train of bioluminescent light that gives the illusion of a swimming creature.

Until recently, researchers needed to use bright lights to capture footage of animals living in the deep dark ocean. The lights scared many creatures away, and when scientists tried filming under low-light conditions, poor camera resolution made it difficult to pick out fine details such as a small ring of light.

In 2016, Haddock’s team attached a 4K camera, which has four times as many pixels per image as a high definition (HD) camera, to one of MBARI’s remotely operated vehicles (ROVs). On one of Haddock’s first voyages with the camera, he recorded a 2.5-centimetre-long animal called an arrow worm emitting a trail of doughnut-shaped rings of blue light. Haddock speculates that the creature uses the display to distract predators as it escapes. “Our HD camera wouldn’t have captured this at all,” he says.

In mid-August, another research team deployed an 8K camera in the deep sea for the first time to explore hydrothermal vents in the Okinawa Trough near Japan. The 8K camera’s resolution nearly matches that of the human eye, and it enabled Dhugal Lindsay, a marine biologist at the Japan Agency for Marine-Earth Science and Technology in Yokosuka, to film near-microscopic plankton in enough detail to identify their species.

Seeing in the dark

Other marine biologists are fine-tuning the latest low-light camera sensors that also reduce noise from scattered, indirect light. This allows researchers to use a lot less illumination to record ocean life, decreasing the chances of their ROVs scaring off animals.

The sensors also allow scientists to pick up phenomena such as bioluminescence — the production of light by an organism — and identify the animals giving off the light show.

“I can’t tell you how many times I’ve seen bioluminescence in the dark and said, 'hey, that was cool, but I have no idea what it is',” says Brennan Phillips, an oceanographer at the University of Rhode Island in Narragansett.

A few years ago, Phillips recorded an as-yet unidentified species of Tomopteris, a marine worm that looks like a centipede, using cameras fitted with advanced low-light sensors. He was able to capture footage of light glowing within the animal’s central nervous system and then radiating into each of its legs.

And on a trip off the coast of Mexico in May, Phillips and other researchers used another new, specialized sensor to record an elusive 68-centimetre-long jellyfish called Deepstaria enigmatica1. This jellyfish lacks tentacles and researchers had long wondered how it captured its prey. The detailed footage showed how the jellyfish moved, which enabled scientists to deduce that the animal ‘bags’ its meal using the thin, membrane-like sac of its body.

Roughly three-quarters of marine organisms, excluding microscopic species and those that live on the sea floor, produce light. But researchers are only beginning to learn how the creatures use this ability to communicate, to attract mates or prey, or to defend themselves, says Haddock.

The footage that he and others are collecting shows animals acting in ways scientists have never before recorded, prompting more questions than answers. “We are going deeper than ‘gee-whiz’,” Haddock says.