During the eight-day Diving Deep for Delicate Drifters expedition, Haddock and team set out to study gelatinous animals like jellies, siphonophores, and ctenophores. Combining blue-water scuba diving near the surface with ROV surveys hundreds of meters underwater, this expedition supported the team’s ongoing work to understand how gelatinous animals have adapted to life in the deep water column.

With science operations complete for the day, MBARI’s submersible pilots were “flying” ROV Doc Ricketts back to the surface for recovery when Research Specialist Shannon Johnson spotted the barreleye and called out for them to stop. Most of the science team had relocated to the ship’s wet lab to prepare to catalog the incoming specimens from the ROV and ran back to the control room, joined by the ship’s crew, when they heard the news. The sighting of a barreleye fish was an exhilarating surprise capping off a long and productive week of deep-sea research.

Past MBARI observations by Senior Scientist Bruce Robison and Research Specialist Kim Reisenbichler were instrumental in revealing this fish’s unique feeding behavior. 

Macropinna lives in the ocean’s twilight zone, scanning the waters above for the silhouettes of prey. Large fins provide stability and maneuverability as a barreleye drifts in place, eyes transfixed on the waters above. After spotting a tasty morsel, those large tubular eyes rotate beneath a dome of transparent tissue to keep prey in sight. The gelatinous shield also protects the fish’s eyes when plucking small crustaceans caught in the stinging tentacles of deep-sea siphonophores. 

The expedition team spent approximately 20 minutes observing the barreleye, leveraging a high-resolution 4K camera on ROV Doc Ricketts to get a closer look at the animal’s body and behavior. They experimented with different lighting conditions to showcase the fish’s unique transparent head shield. ROV Pilot/Technician Cameron Law was even able to maneuver Doc Ricketts close enough to film the fish with the vehicle’s VR camera, capturing 3D stereo imagery that can contribute to future education and outreach efforts.

Scientists in the Biodiversity and Biooptics Team study how marine animals interact with light. They have conducted extensive research on the visual systems of deep-sea animals. MBARI researchers did not collect this barreleye, but the footage they recorded will be a vital resource for continued research on this elusive species. Their close-up examination of the eyes of Macropinna will help the team better understand vision in the dim depths of the ocean’s twilight zone. The pigments in the lenses of the fish’s eyes are thought to serve a similar function as the green pigments in the eyes of the strawberry squid (Histioteuthis heteropsis), one of the barreleye’s deep-sea neighbors that the Biodiversity and Biooptics Team has studied in the past.

“Macropinna reminds us of the surprising ways that animals have adapted to thrive in the ocean’s midwater,” said Haddock. “So many of them survive by looking for subtle optical cues, like a shadow passing overhead, and this sets off evolutionary competition, pitting bioluminescent camouflage against increasingly sophisticated visual capabilities.”

In nearly 40 years of ocean exploration, MBARI has completed roughly 7,000 ROV dives and recorded more than 41,000 hours of deep-sea video, yet we have only encountered this species 11 times. MBARI’s last sighting of Macropinna was in 2021. This recent sighting is our first to be filmed in 4K and the first from MBARI’s new flagship research vessel. This summer, MBARI researchers leading an expedition with Schmidt Ocean Institute in the mid-Atlantic Ocean recorded footage of another species of deep-sea barreleye, the binocular fish (Winteria telescopa).

The Diving Deep for Delicate Drifters expedition was made possible thanks to the David and Lucile Packard Foundation’s longtime support of MBARI’s work.

Learn more about the barreleye fish.

Read logs from the Diving Deep for Delicate Drifters expedition.

Story by Senior Science Communication and Media Relations Specialist Raúl Nava

For additional information or images relating to this article, please email pressroom@mbari.org.