Scientists from the Woods Hole Oceanographic Institution (WHOI), University of Hawaii, Whitman College and international colleagues will conduct the first systematic study of life in the deepest marine habitat on Earth—ocean trenches.
Due to the extreme pressures of these deep-sea environments and the technical challenges involved in reaching them, ocean trenches are among the least explored environments on the planet
The team was awarded a $1.4 million collaborative grant from the National Science Foundation for a three-year program of studies in ocean trenches whose depths range from 19,685 to 36,089 feet (6,000 to 11,000 meters), known as the hadal zone.
The program takes advantage of recent advances in imaging and collecting technology, and the sampling and exploration capabilities of the deep-diving Hybrid Remotely Operated Vehicle Nereus, which explored Earth’s deepest trench—the Mariana— in 2009, to provide new and unprecedented access to the deepest parts of the ocean floor.
The Hadal Ecosystem Studies (HADES) program includes international collaborators at the University of Aberdeen (UA) in Scotland, National Institute of Water and Atmospheric Research (NIWA) in New Zealand, and The National Oceanography Centre (NOC) at the University of Southampton.
“The program is global in scope. The goal is to conduct detailed studies of the composition, diversity, and adaptations of life in the major deep ocean trenches and then compare these findings between the trenches around the world,” said Tim Shank, a deep-sea biologist at WHOI and lead investigator on the project. “No single trench has been biologically characterized in this detail.”
The work will begin in 2013 at the Kermedec Trench, off the northeastern tip of New Zealand's North Island, and will later include expeditions to the Mariana Trench near the island of Guam in the west Pacific.
At 750 miles long and 32,963 feet (10,047 meters) deep at its deepest, Kermedec is one of the coldest trenches in the world due to the inflow of deep-water originating from Antarctica.
The 2013 expedition will build on recent studies of the Kermadec Trench by HADES program collaborator Alan Jamieson at UA’s Oceanlab and colleagues at NIWA and the University of Tokyo. Using a state of the art, free-falling autonomous baited camera system, the research team documented many new species of animals in the Kermadec and other trenches around the Pacific Rim in the past few years.
Prior to that work, what little is known about life in ocean trenches came from grab samples and trawling done by scientists in the 1950s. When scientists first dredged and cored the trenches, they were able to create lists of the species present. At that time it wasn’t possible to determine from where in the trench the various animals came, exactly what depths, or whether they were living on the sides or right in the trench axis—the deepest point.
“We know from earlier work what species of animals we’re likely to find there,” Shank said. “But we have no idea how these animals make up trench ecosystems or how they are organized. This will be a first-order look at community structure, adaptation, and evolution—how life exists in the trenches.”
Life in the Trenches
With icy temperatures, no sunlight, and intense pressures, ocean trenches provide a hostile environment for living things. Once thought to be devoid of life, trenches may actually be home to many unique species. For one reason, food is plentiful there. Organic material in the ocean gets moved by currents and pulled down into the trenches.
“We know there’s an excess food supply in the trenches, which means it can support more and potentially highly-diverse life forms,” Shank said. “Through systematic imaging and sampling we are looking to discover how trench ecosystems are put together and through analyzing their DNA, how species have evolved to be specific to trenches from what we see in other parts of the ocean.”
In addition to looking at how food supply varies at different depths both in the trench and in the abyssal plain—flat areas of the seafloor usually found at depths between 3,000 and 6,000 meters—the research team will be investigating the role energy demand and metabolic rates of trench organisms plays in the community structure and how it differs from shallow water relatives.
“The energy requirements of hadal animals have never been measured before,” said Jeffrey Drazen from the University of Hawaii, who will lead the efforts to study distribution of food supply and the energetic demands of the trench organisms. “Metabolism is the process of energy partitioning and utilization and can give us an estimate. Some deep-sea animal groups have 10-fold lower metabolic rates than shallow living species.”
Scientists aren’t sure if the animals adjust their requirements strictly to match the food supply or if other factors are at work. Some studies, by Drazen and others, suggest the declines in metabolism stop below about 1,000 meters while food supply (phytoplankton in surface waters) continues to decline with depth.
“Instead the declines in metabolism may be related to light levels and the animals abilities to see predators and prey and react to them,” Drazen said. “Brightly lit surface water makes predators and prey visible over longer distances, resulting in species with robust locomotion to chase or evade, and hence high metabolism. In the dark deep sea, the distances over which eyed predators and prey interact shrinks, and with it locomotory ability and metabolism.”
The animals that have been previously studied were almost all from depths less than 2,000 meters and in areas where both food supply and light decline with depth.
“In the trenches, we suspect food supply increases with depth but, of course, it will be dark throughout. We can test the competing theories,” Drazen said. “We will measure metabolism by placing the animals into small chambers using the HROV Nereus and measuring how fast they consume oxygen. Our experiments will be some of the first manipulative experiments in the hadal zone. Regardless of which hypothesis is correct, the metabolism data will help us understand how food supply regulates the distribution and density of hadal animals, which can help us put together a picture of the flow of energy throughout the food web.”
Exactly how animals in the trench evolved to withstand the pressures is not completely known, but scientists are putting together pieces of the evolutionary puzzle. They know that hydrostatic pressure, which at depths found in ocean trenches can be up to 1,100 times that at the surface, is known to inhibit the activity of proteins.
HADES program collaborator Paul Yancey from Whitman College will be investigating the role that piezolytes—small molecules that protect proteins from pressure— play in the adaptation of trench animals. The use of piezolytes, which was developed and discovered by Yancey and his students, is a novel hypothesis and attempts to explain previous findings that not all deep-sea proteins seem to be able to evolve resistance to pressure within their structures.
“I am trying to discover how life can function under the massive pressures of the hadal zones. This is important because pressure might very well be the primary factor determining what species can live there,” Yancey said. “High hydrostatic pressure in essence inhibits and distorts biomolecules like enzymes and other proteins. One way this happens is that pressure traps dense layers of water molecules around proteins, making it harder for proteins to bind to other molecules which they must do as part of their function.”
At more moderate depths, there is evidence of life adapting to pressure in two ways: by evolutionary changes in protein structures that make those molecules more resistant to pressure effects; and with piezolytes, which seem to help remove the dense layers of water trapped around proteins, Yancey said.
“What we don't know is whether either or both mechanisms work at the greatest ocean depths, and whether they work in all kinds of organisms or only some,” he added. “These are questions we hope to answer.”
In addition to deep-sea life with novel adaptations, there is also evidence to suggest that trenches act as carbon sinks, making the research also relevant to climate change studies. The V-shaped topography along trench axes funnels resources—including surface-derived organic carbon— downwards.
“Trenches are the largest unexplored biome on Earth,” Shank said. “The bulk of our knowledge is only from snapshot visits using mostly trawls and camera landers. Only detailed systematic studies from a team will advance our biological understanding of deep trenches, and also reveal the role hadal trenches may play as the final location of where most of the carbon and other chemicals get sequestered in our ocean, impacting the global carbon budget and ultimately climate.”
The HADES program will utilize the deep-diving Hybrid Remotely Operated Vehicle Nereus, which was developed by a team of engineers at WHOI. First conceived in 2000, it took nine years to design and build the vehicle.
On its first mission in May 2009, Nereus successfully dove to the deepest part of the ocean—Challenger Deep in the Mariana Trench. At about 36,000 feet (11,000 meters), the deepest part of the trench extends farther below the sea surface than Mount Everest reaches into the sky.
Nereus was the first vehicle to explore the Mariana Trench since 1998, when the Japan Agency for Marine-Earth Science & Technology’s remotely operated vehicle (ROV) Kaiko made a series of dives there. Kaiko was lost at sea in 2003, and no other ROV was capable of reaching full ocean depths until the development of Nereus.
In October of 2009, researchers successfully used Nereus to investigate hydrothermal vents along the Cayman Trough—the deepest point in the Caribbean Sea with a maximum depth of 25,217 feet (7,686 meters).
“With a robot like Nereus, we can now explore virtually anywhere in the ocean,” said Andy Bowen, the project manager and principal developer of the vehicle. “It marks the start of a new era in ocean exploration and research.”
The deep-diving, unmanned vehicle can operate either as an autonomous, free-swimming robot for wide-area surveys, or as a tethered vehicle for close-up investigation and sampling. The vehicle will allow HADES program researchers to gather high definition video along the trench axis, as well as recover organisms and sediment samples.
The HADES program will also utilize technology designed at the University of Aberdeen’s Oceanlab. Jamieson and colleagues at NIWA and the University of Tokyo first used the Hadal-lander—an ultra-deep, free-falling baited camera system— during a project called HADEEP (HADal Environments and Education Programme), a five-year collaborative effort to study trench life.
The landers, which are equipped with either full ocean depth rated video (Hadal-Lander A) or still camera (Hadal-Lander B), have amassed tens of hours of high-resolution video and tens of thousands of digital still images from five of the deep trenches around the Pacific Rim since 2006. They are pre-programmed prior to submergence, deployed in free-fall and sink to the trench floor using heavy ballast weights. Once on the seafloor, hadal organisms are attracted to the lander by locally sourced bait and imaged by the cameras. At the end of the dive, the ballast weights are jettisoned by acoustic command from a surface vessel, and they ascend to the surface.
“To date, this method has been successful in observing the deepest fish ever seen alive,” Jamieson said.
The landers are also equipped with small invertebrate funnel traps to collect small crustacean samples. The technology prompted new insights into the distribution of amphipods—crustaceans related to shrimp—in multiple trenches. More recently a new hadal-lander (LATIS) was constructed as a dedicated fish trap and successfully recovered both hadal fish and ‘supergiant’ prawns in the Kermadec Trench.
“By combining WHOI’s HROV Nereus with Oceanlab’s Hadal-Lander technology, the team have the best available technology at their disposal,” Jamieson said. “The HADES project is extremely exciting as it combines a comprehensive baseline biological survey at depths we know little about with high profile and state of art deep-sea technology to conduct biological research.”
The Trench Connection
The development of the Nereus vehicle and new discoveries from the HADEEP project prompted scientists to hold the first international symposium on hadal zone studies. The Trench Connection symposium, which was held at the University of Tokyo's Atmosphere and Ocean Research Institute in November 2010, brought together deep-sea biologists and engineers from all over the world to discuss the latest developments in deep submergence technology and identify the foremost questions that remain in understanding the deepest environments on Earth.
“The meeting not only helped identify the critical questions that need to be addressed in ocean trench research, it helped us gather the expertise to tackle those questions,” Shank said.
“The HADES team comprises a unique team of deep-sea scientists from around the world, bringing together the best skills in molecular, metabolic, physiologic, explorative, ecological and genetic disciplines. There has never been a trench project undertaken with such a variety of expertise and deep-submergence technology,” added Jamieson.
It was no coincidence that an international gathering on ocean trench studies was held in 2010. January 23, 2010, marked the 50th anniversary of the pioneering dive to Challenger Deep in the Mariana Trench by Jacques Piccard and Don Walsh in the U.S. Navy-operated bathyscaphe Trieste.
On March 26, 2012, filmmaker James Cameron became the first person to make a solo dive to the deepest part of the ocean in his submersible, the “Deepsea Challenger.”
While exploring the ocean’s “final frontier” is certainly part of the allure of the HADES program, Shank is quick to point out that it’s about much more than just exploration.
“We’re trying to answer fundamental questions about how life exists and has evolved on our planet—in our deep ocean. Over the years, we’ve made large leaps in understanding life at deep-sea hydrothermal vents, seeps and seamounts, but we know relatively little about life in our ocean trenches,” Shank said. “That’s what makes this project so exciting. There will be major impacts on our understanding about life on Earth as a result of doing this work.”
The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, in Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the oceans’ role in the changing global environment. For more information, please visit www.whoi.edu.