Expedition log by MBARI President and CEO Antje Boetius

Diving to a seamount always comes with surprises. Such underwater mountains can reach thousands of meters above the seafloor, forming unique ecosystems. Like islands in the sea, they attract and sustain their own communities of marine life. I have studied seamounts in almost all oceans, including the ice-covered polar seas, and was always intrigued by the abundance of life they host, be it corals, sponges, fishes, or anemones. 

Often, the densest communities are found at the top of the mountain. Not so at Davidson Seamount, where “Octopus Garden” was found at the base in more than 3,000 meters (approximately 9,800 feet) of water. When I learned years ago from Senior Scientist Jim Barry about the discovery of thousands of breeding octopus here, I was fascinated and wished I could one day go out to sea and see this amazing find for myself. 

Today was the day when this wish was fulfilled: At about 9:00 a.m., the dive with MBARI’s remotely operated vehicle (ROV) Doc Ricketts reached the seafloor, and minutes later, we saw the first octopus, guiding the way to a huge accumulation of female cephalopods, called “Octopus Spa.” I have never seen anything like it. In literally every crack of the rocky seafloor, where warm fluids are seeping up from below, an octopus mother forms a nest. To do that, they flip their arms above their head for protection and cover dozens of eggs with their large body, breathing slowly but steadily through their siphons. From a distance, they look like violet soccer balls. 

What a fantastic opportunity for me to come along to better understand MBARI’s art in ROV operations and the integration of observation and experimentation using our new ship, R/V David Packard. It is really busy on deck starting with sunrise. Before and after the dive, there are moorings to place, CTD (conductivity, temperature, and depth) profiles to measure, and multibeam mapping to do. For the ROV, it takes about 1.5 hours to dive down to 3,000 meters and 1.5 hours to come up, so we have about six hours at the seafloor to work and enjoy. Obviously, I am now in love with Doc Ricketts.

It is simply stunning how, by zooming into the nests with the 4K cameras, we can film the hatching of little baby octopus, which leave the nest with amazing determination. MBARI’s skilled submersible pilots use the ROV’s large titanium manipulator arms to carefully pluck some sea anemones, feather stars, and other delicate critters around the nests. 

One important question is about the food web developing around the octopus’s breeding grounds: How does the presence of one species create a niche for so many others to thrive? Answering this requires video transects, taxonomic analyses, and probes of tissue, to tease apart who feeds on whom. For the broader ecological context, the biochemical signatures of Octopus Garden are archived by pumping bottom water into Niskin bottles, which are later filtered for environmental DNA (eDNA) analyses. 

What a pleasure to learn how we can explore the secrets of this and other fertile subsea landscapes of life out here on the California margin.