Expedition log by Senior Scientist Jim Barry

R/V David Packard is steaming back toward Moss Landing, and after 10 days at sea, we’ve accomplished nearly all we set out to do. Behind us, we’ve left a network of instruments—some of them recording for the next full year—designed to test a single idea: that Davidson Seamount, through its interaction with ocean currents, concentrates and enriches the life around it.  

Is Davidson Seamount a biological hotspot? 

The seamount effect 

Some seamounts are known to boost both the diversity and the sheer abundance of animals nearby, from the base to the top of food webs. The mechanism is largely physical. When a current encounters an underwater mountain, flow is deflected and accelerated around it, delivering more suspended food to corals, sponges, and other filter-feeders anchored on the slopes. Additionally, nutrients may be upwelled and stimulate phytoplankton growth if the seamount peak is shallow enough to sit in the photic zone. The surplus in productivity can cascade upward through the food web—more filter-feeders support more fishes and cephalopods, which in turn support predators as large as whales. 

This idea is usually applied to the upper ocean. We suspect it also operates in the abyss and the cold and permanent dark at the seamount’s base. 

Furrows on the seafloor 

Our 2020 exploration around Davidson Seamount turned up something we rarely see: numerous jagged gouges in the seafloor mud, each roughly two meters (6.6 feet) long. Despite decades of seafloor observation across this region, we’ve seen only a handful of these features. 

We suspect that they are the work of deep-diving beaked whales foraging for cephalopods and fishes, and this supposition stimulated the research carried out on this cruise. We hypothesize that the furrows are more common near Davidson Seamount—and perhaps near other seamounts—precisely because of the enrichment effect described above. If foraging whales are making these scars, the whales are presumably benefiting from the seamount: prey may be more abundant near it, easier to capture, or both. 

The toolbox 

We left port with the back deck of the David Packard crowded with gear and a straightforward experimental design: two study sites near Davidson Seamount and two control sites far enough away to be outside its influence (see map). 

At each site, we deployed hydrophone moorings that will record continuously for a year, capturing any sound within a two- to three-kilometer (one- to two-mile) radius. We dropped baited time-lapse cameras for shorter intervals to document the scavenger community. Remotely operated vehicle (ROV) Doc Ricketts flew transects just above the bottom, surveying seafloor animal life and looking for fresh evidence of beaked whale foraging. 

Each night, a rosette sampler collected water from depths spanning from the bottom to the surface for environmental DNA (eDNA) analysis—the genetic material organisms continuously shed into the water, which lets us inventory a community without ever laying eyes on it. Sediment samples we collected will feed into the same analysis, including paired samples taken from inside recently formed gouges and from the undisturbed seafloor alongside them. Late nights were reserved for acoustic surveys of prey density. 

Early returns 

Our preliminary comparison across the four sites largely supports the notion that beaked whales are more active near Davidson Seamount than away from it. 

The key to a definitive answer, though, is sitting on the seafloor right now, listening. We will return next year to recover moorings and continue our observations. We can’t wait to analyze hydrophone recordings and compile datasets to see if we detect the signature of the “Davidson Seamount Effect.”