Nereus
Photo by Advanced Imaging & Visualization Lab ©Woods Hole Oceanographic Institution.

The ocean vehicle Nereus implodes on a six-mile-deep dive, witnessed by Whitman Professor of Biology Paul Yancey.

By Mackenzie Gerringer ’12, Gemma Wallace ’14 and Professor of Biology Paul Yancey

Paul: I study adaptations to high pressure in deep-sea animals. Recently, I co-wrote a proposal to the National Science Foundation to extend my research into the planet’s least-explored habitat, the deep-ocean trenches known as hadal (“of Hades”) zones for their harsh conditions of low temperatures, eternal darkness and highest ocean pressures. A full survey of topography, ecosystems and adaptations in the trenches, which run from 6,000 meters to 11,000 meters maximum in the Mariana Trench, has never been done; we actually know more about the surfaces of the Moon and Mars! The geology of the trenches, which are sites of major earthquakes and tsunamis, is also poorly known. Exploring this realm is a daunting and risky task, as the vast majority of marine equipment cannot function at depths below 6,000 meters. The proposal sought to use a variety of advanced pressure-hardened technologies: camera landers (which descend to one site and film animals attracted to bait), traps and Nereus, the world’s only robotic submersible capable of full ocean depth. Built at the Woods Hole Oceanographic Institution, Nereus was designed to cruise along the seafloor filming with five different cameras (including one HD set donated by director James Cameron) and to grab specimens with a high-tech manipulator arm. Nereus was controlled remotely from a mother ship via a hair-width fiber optic cable.

From this proposal was born the NSF-funded HADES Project (Hadal Ecosystem Study), an international collaboration of 32 scientists, postdocs, students and Nereus engineers from six countries. HADES’ first mission – 40 days on the Research Vessel Thompson – was to the Kermadec Trench, which plunges to a depth of 10,000 meters and runs northeast of New Zealand (where we boarded) towards Samoa (where we disembarked). The team included three from Whitman – Gemma Wallace ’14, Mackenzie Gerringer ’12 (a graduate student at the University of Hawai’i, one of the collaborating institutions) and me.

All: Life at sea is exhausting in the best possible ways. We ran operations around the clock, with deployments up to 10,000 meters. The days all blur together in one big dance – standing watches, deploying traps and landers, logging Nereus discoveries, recovering gear, processing animal and sediment samples, repeating again … cherishing the occasional two hours in the rack when we could. We were sustained by the excitement of discovering something new from each depth. Every dive has this palpable anticipation and potential, so we keep working, even through times of failure – and there were many of those in this high-risk project: the Nereus cable broke several times, its winch was damaged by the fringes of a passing cyclone, one lander camera was destroyed by pressure and, most traumatically, Nereus itself imploded under pressure after finishing most of its deepest (10,000 meter) survey.

Supergiant amphipod found at 7,100 meters. Photo by Paul Yancey.Despite this loss, Nereus conducted a record-setting set of surveys at depths up to 10,000 meters. In addition to dozens of hours of high definition videos and many animals, the vehicle collected mud cores that will help collaborators measure carbon input in the trench. This will be critical knowledge for climate research as we know that some of Earth’s carbon recycles through the trenches, but we do not know how much. We also discovered new species and behaviors, and that ecosystems change rather dramatically with depth over smaller distances than previously thought. At the shallower depths, dives revealed deep-sea specimens found worldwide, including rattail fish, cusk eels and amphipods, universal ocean scavengers familiar to most as those near-microscopic “beach fleas” hopping around kelp debris on beaches and relatives of your tiny garden pill bugs. Diving to true hadal depths at 6,500 to 7,000 meters, things really changed. On rocks were “gardens” of sea lilies (crinoids), a stalked echinoderm group that was far more widespread in the oceans millions of years ago. In large numbers were numerous amphipod species including the “supergiant” amphipod.

Gemma: Amphipods are perhaps the best model animals for studying adaptations to extreme pressure. They are one of the few groups to live across all ocean depths, and they can be readily collected in large numbers with baited traps. Among the many species we collected, one specimen was especially striking: a “supergiant” brought up from 7,000 meters. “Supergiant” is an excellent way to describe this animal: compared to those tiny beach fleas, these are enormous, up to almost a foot long! An eerie, translucent yellow, supergiants are uncommon and mysterious creatures. This special specimen will shed light on how biochemical adaptations allow animals to survive the extreme conditions of the deep sea. Thus far, we have identified a number of compounds in deep-sea amphipods that may protect them from the crushing effects of extreme pressure. Interestingly, some of these compounds may have biomedical applications, and one is currently being tested in drug trials for Alzheimer’s disease.

Mackenzie: Also found in surprisingly large numbers were – in my admittedly biased opinion – one of the most fascinating fish in the sea, the hadal snailfish. These are the deepest-living fish and the lone vertebrates from about 6,500 to 8,000 meters. This particular species of hadal snailfish is exclusively native to the Kermadec Trench. These little pink fish feast on amphipods. Incredibly, they have no scales, just a thin, transparent layer of skin and a gel-filled body that leave their internal organs visible even in Nereus footage. Prior to this cruise, only a handful had ever been caught. Our collection from this cruise will be groundbreaking in understanding these amazing animals.

All: At 8,100 meters and deeper, no fish live (Paul has proposed that this is due to their inability to cope with the highest pressures). Unchecked by predatory fish, amphipods were seen swarming in staggering numbers, scavenging anything dead that sinks to the bottom and eating each other – not just carnivorous but also cannibalistic! We even found a mysterious eight-armed gelatinous animal seemingly new to science.

Mackenzie: Seeing the few shattered pieces of Nereus rise to the surface further instilled in me a sense of awe at the barely fathomable extremes of the environment into which we delve. It is one thing to know the number 10,000 meters, or to cite your favorite depth factoid (far deeper than Everest is tall, the psi equivalent of 8,000 elephants standing on a car). It is something else entirely to witness the power of that amount of pressure. It makes me marvel ever more profoundly at hadal animals such as the snailfish – so seemingly fragile – are positively thriving under the crushing weight of 7,000 meters of water.

With the misfortunes of this cruise in mind, it may seem odd that this is my dream job. My hands smell relentlessly of fish bait; I spend a good part of my day squeezed into a fish trap tying knots from awkward angles; I have earned more bruises than I can count and we work around the clock for weeks. But I can say without a doubt that this is exactly what I want to be doing. We’re pulling back the curtains on one of our planet’s most extraordinary and least understood habitats, an area that so few have glimpsed at all.

All: There is an innate curiosity and attraction to understanding the extremes of life and pushing the extremes of technology. We’re always looking to know the limits, to challenge them, to redefine them. This perpetual drive for progress and exploration is something very fundamental to the human spirit. For us, trench exploration embodies these goals. We will continue to develop and harness the technologies that allow us to discover and understand the species with whom we share our planet.