When we think of animal eyes, humans, birds, and cephalopods might come to mind. But gelatinous animals like medusa jellies also have eyes that vary in complexity and rely on light sensing for several important biological functions. In the deep sea, the dominant light deep-sea animals detect isn’t sunlight, but living light: brilliant displays of bioluminescence. Although these phenomena are common in the ocean, we know surprisingly little about the full diversity of ways organisms interact with light. One of our main goals as a research team is to better understand how animals produce and sense bioluminescent light in the ocean.

On this research expedition aboard R/V David Packard, we are collecting animals to characterize their light-sensing capabilities, document their bioluminescent displays, and prepare samples for further study using the advanced genetic and biochemical tools we have on shore. 

We are particularly interested in examining poorly-studied animals with unique light-producing and light-sensing chemistries to better understand the evolution of these traits across the tree of life. So far, we have successfully collected many samples that will be useful for this. During our blue-water scuba dives near the surface and collections with MBARI’s remotely operated vehicle (ROV) Doc Ricketts thousands of meters underwater, we encountered numerous medusae, ctenophores, and siphonophores, including some deep-sea medusae with pigment eye spots in unusual places and shallow-water ones with eyespots that make them strongly reactive to light.

On two of our ROV dives to below 2,000 meters (6,560 feet), we were lucky enough to encounter a rare bathypelagic nudibranch—a swimming snail—called Bathydevius caudactylus, which was described in 2024 by MBARI scientists Steve Haddock and Bruce Robison. We were really excited to find them because this species is one of the few known bioluminescent swimming nudibranchs, and its biochemistry is completely unknown. 

We were able to collect these two nudibranchs and observe them in our shipboard dark room to document their bioluminescent properties, including the color of their light, which is a beautiful blue-green. We preserved the samples for further study to identify the genes responsible for light production and compare them with those in other known bioluminescent systems. 

On this trip, we’ve also collected a number of other bioluminescent animals, including sponges, polychaete worms, and comb jellies, as well as filmed light displays in situ using an ultra-sensitive low-light camera mounted on the ROV. We’re really excited to see what we learn from all of these amazing animals!