Expedition log by MBARI Graduate Research Assistant Anik Grearson

We woke up bright and early with the sunrise to launch remotely operated vehicle (ROV) Doc Ricketts on a dive to 2,200 meters (approximately 7,200 feet) below the surface at a station north of Davidson Seamount, an underwater mountain offshore of Central California. While part of our team stayed in the control room and worked with the ROV pilots to observe and collect deep-sea midwater animals, Steve, Lena, Shannon, Drew, and I set off in a smaller boat to collect shallow-water animals just below the surface using a specialized scuba technique called blue-water diving. In this setup, divers are tethered together via a central down-line to control our descent and ascent, and so we don’t drift too far apart from each other. 

The amazing team on R/V David Packard got the dive boat safely over into the water, and we motored off with our trusty boatswain, Scott, at the helm. Today, a pod of common dolphins joined us, playfully leaping out of the water and riding the bow of the small boat as we headed a kilometer away from the larger vessel. Once on station, we donned our gear, rolled backward into the water, clipped into our lines, and dropped down 18 meters (60 feet) below the surface. We found ourselves surrounded by gelatinous animals of all kinds: delicate jellies, beautiful siphonophores, large salp chains, and hungry ctenophores! The water surrounding us had a bluish-green tinge, and the sunlight shining from above illuminated the near-invisible creatures we were seeking. Many of these animals are so fragile that the only way to truly see their natural behaviors and morphology is on a blue-water dive like this. 

We sometimes encounter rare and unexpected organisms on blue-water dives. Today, we found a species of tropical ctenophore called Ocyropsis, which has muscular lobes that it uses for quick swimming to escape predators. We also found a beautiful pink siphonophore, Athorybia rosacea, which uses its stinging tentacles like a jig to catch its prey. We typically only see Ocyropsis and Athorybia in warmer waters farther south, so we were surprised to find them 60 miles off the coast of Big Sur, California. As El Niño strengthens, warm water is moving up the California coast. During past El Niño events, we have seen visitors from tropical waters here in Central California, so we expected to see some southern species venturing farther north. We even encountered a tiny ribbonfish larva who greeted us with its long, thread-like fin rays.

We carefully collected a variety of gelatinous animals in glass jars and brought them back to R/V David Packard for closer inspection. Back on the ship, our team examined, photographed, and preserved these specimens for scientific study. Our lab is particularly interested in gelatinous marine animals, such as ctenophores, jellies, and siphonophores. These precious samples will allow us to answer many new biological questions, including:

• Many ctenophores, siphonophores, and jellies produce their own light, a phenomenon known as bioluminescence. How do they do that? Why do they do that?
• Some jellies also have light-sensitive structures and even simple eyes. What is the molecular and genetic basis of light detection in these animals?
• Some of these shallow species have relatives living much deeper, even several thousand meters below the surface. How do some species survive in the deep sea, where the pressure is immense and temperatures drop to near freezing, while other species live only at the surface?
• The open ocean has seemingly no geographic barriers, so how do distinct populations of gelatinous pelagic species occur?  

After a productive morning of diving and processing samples, we had a delicious lunch prepared by the ship’s incredible cook, Sue. The next step is to get ready to process the precious deep–sea specimens coming up on the ROV, which usually takes us into the late evening. Then we get up tomorrow and do it all again! We hope our wetsuits have dried out a bit before the morning. While these long days at sea are a lot of work, very few people get to encounter these weird and wonderful animals, so I feel very lucky to be a part of this expedition exploring the largest and least understood habitat on our planet.