This month, Museum Curator John Sparks is leading The Explore21 Solomon Islands Expedition. A part of the Museum's Explore21 initiative, this three-week research journey is headquartered aboard the Research Vessel Alucia.
Expedition member Chris Filardi, who is the director of Pacific Programs in the Museum’s Center for Biodiversity and Conservation, recently wrote in with this dispatch.
One of the most exceptional aspects of this expedition is ready access to deepwater submersibles or submarines. These allow us to probe depths that are out of reach to even the deepest SCUBA divers and beyond, into the aphotic zone where sunlight cannot penetrate—the darkest place on the surface of the Earth.
Alucia’s yellow submarine doesn’t just get us there. It can also carry equipment impossible for a swimming diver to transport and operate.
And, unlike a SCUBA diver breathing compressed air or other mixed gases, the sub allows scientists to linger at depth for hours, without the need to clear their bodies of excess nitrogen. Lingering at depth enables new kinds of data collection, high-tech imaging, and novel observations of behavior, all of creatures rarely seen as specimens, let alone alive in their natural habitat.
Each dive begins with a long sequence of battery charging, filling compressed air (for buoyancy compensation) and re-breather chambers (with pure O2), checking tracking, communications, and safety gear, and then readying the harness on the Yellow Submarine for launch. Instead of small portholes of subs in the past, the Alucia’s Triton sub Nadir has a large acrylic sphere that houses the cockpit. Capable of withstanding the crushing pressures of deep ocean, the acrylic has nearly the same refractive index as water, meaning it disappears when submerged, giving scientists the sensation of actually being surrounded by the sea, without getting wet or requiring SCUBA gear.
That sphere does come at a price. It is very buoyant, 2 tons worth. The sub must compensate for all that float power to be able to dive, and this makes it very heavy. On Alucia this problem is solved by a 21-ton A-frame crane that lifts the sub from the aft deck and swings it out over the sea, gently lowering the craft into the water. And then she is off and down, into the underwater habitats home to animals and natural phenomena that are the focus of this expedition.
Sub dives will generally have one or two primary scientific objectives that determine the depth and trajectory of the dive and ascent. Right now the sub is ascending from a night dive down to nearly 950 meters with a focus on capturing bioluminescent organisms in action. A big swell makes the sub recovery quite dramatic, as it swings pendulum-like before the crew. Some of us help to stabilize the Nadir as she comes aboard safely at around midnight.
Previous dives have focused on using specialized lighting and filter systems to visualize the remarkable worlds of fluorescent color invisible to humans but, based on studies of fish eyes aboard Alucia, apparently visible to many fishes. We have also used baits to draw in scavengers that roam the abyss, with eerie results: a ravenous chambered nautilus relishing a meal, an odd benthic shrimp, a few shy passes of a strange deepwater shark.
Tonight’s dive was in open water and focused on using the sub’s specialized low-light cameras to film bioluminescence. By flashing white light in different patterns, team members Vincent Pieribone, of the Pierce Lab at Yale University, and David Gruber, a Museum research associate who is at the City University of New York, are able to “excite” animals that respond with a dazzling light show that scientists are just beginning to understand.
Ramifications of these studies are twofold. First, the high-tech imagery combined with the ground-breaking systematics work that John Sparks is doing enables us to probe the biological significance of bioluminescence. In the night sea, animals are literally talking with light—at almost light speed. The team is finding that organisms responding to light stimuli in the pitch black have an almost immediate luminescent response. This is a real surprise of the trip, which leads to the second upshot of our work. Near-instant response times expose a cellular system absolutely unique to bioluminescent organisms.
Ultimately, for neurobiology, or the study of the machinery of nervous systems, this vanishingly narrow cellular time horizon between light reception and light production can be co-opted or mimicked and placed into human cells to reveal otherwise invisible processes of disease or health. A real and profound potential, but for now, most of us on board are simply reeling from the universe of moving lights swarming along the reefs and sea mounts of far-flung islands.
See all dispatches from the Explore21 Expedition: