KINGSTON — To Brennan Phillips, University of Rhode Island assistant professor of ocean engineering, it was an unparalleled sight.
In the depths of the sea off the Solomon Islands in the South Pacific, he and a team of researchers saw what he described as “a magic carpet of stars.” The stars were actually bioluminescent lights emitted from thousands of flashlight fish (Anomalops katoptron). The team’s findings demonstrated that the fish synchronize bioluminescent flashes in order to organize as a school in the absence of ambient light.
The study, led by American Museum of Natural History researchers, reveals a novel function for bioluminescence in ocean waters. It also raises the possibility that fish schooling may occur in the deep sea, where it had been assumed to be too dark for fish to coordinate their movements as a group. The study was published Wednesday in the journal PLOS ONE.
Through an analysis of video recordings and modeling, Phillips and the other researchers were able to demonstrate that flashlight fish are, in fact, swimming in a well-organized position relative to one another, as opposed to “shoaling,” a looser form of grouping.
“Fish like to communicate. This is something we’ve known, but to be able to show that quantitatively, and to share supporting video footage that we were able to get, is remarkable,” he said.
Bioluminescence is the ability of living organisms to generate visible light through organic chemical processes. Flashlight fish, which tend to hide in caves and reef crevasses by day, go out to explore only on moonless nights. The fish have pockets containing bioluminescent bacteria located beneath their eyes, which they manipulate to create flashing patterns.
The research team serendipitously came across a school of thousands of flashlight fish while diving off the Solomon Islands.
They collected video images of the school — the largest recorded aggregation of bioluminescent flashlight fish — as part of a 2013 trip, and returned to the remote, uninhabited volcanic island in 2016 and 2019 to gather more data.
Phillips modified a deep-sea low-light camera system so it could be used by scuba divers.
“Everything had to come together to get these data—the new camera system, the weather, the divers, and, of course, the fish," he said. "It was one of the hardest challenges I have faced as a marine roboticist.”
To capture video of the fish’s nighttime behavior, observations had to be made without artificial light. Both divers and a three-person submarine used a suite of low-light cameras, including a custom-built underwater high-speed, high-resolution scientific complementary metal-oxide-semiconductor (sCMOS) camera.
“What we saw and experienced was truly extraordinary,” Phillips said. He calls the flashlight fish “the fireflies of the sea” and said he hopes that his team’s project will inspire more research.
Other authors of the study include lead author David Gruber of Baruch College, who also serves as a research associate at the American Museum of Natural History; Rory O’Brien, Ganesh Vasan, Peter O’Brien, and Vincent Pieribone, from the Yale University School of Medicine; and Vivek Boominathan and Ashok Veeraraghavan, from Rice University.