Scripps researchers uncover the mysteries of the planet’s deepest, darkest secrets
The deep sea, Earth’s largest ecosystem, also remains its least explored frontier. Humanity’s ideas of the deep ocean have long been misconceived; not long ago scientists perceived the deep as a barren and lifeless abyss. However, researchers at Scripps Institution of Oceanography at UC San Diego are now shedding light on the ocean’s darkest depths and sharpening science’s characterization of the deep’s unique features, as well as the bizarre and fascinating inhabitants that call it home.
The bone munchers
When it comes to strange inhabitants of the deep, here’s one of the most bizarre: Osedax, a feathery, mouthless and gutless creature known as the “bone worm” because it secretes acid on dead whales and other carcasses in order to consume their bones for sustenance. But if their appetite sounds strange, think of their social life. Where researchers once thought large female bone worms were found to dominate over harems of tiny dwarf males, in late 2014, Scripps’ Greg Rouse and his colleagues announced the startling finding of an evolutionary reversal: large males were discovered that were tens of thousands of times larger than their previously studied male counterparts.
“The discovery was very unexpected,” says Rouse. “It’s the first known example of such a dramatic evolutionary reversal from dwarf males.”
And if the story wasn’t odd enough, Rouse and his colleagues probed deeper and found that the newly discovered males offered an even stranger element related to their mating habits. Previously studied Osedax male dwarfs were permanently attached to their female hosts, and therefore did not need mobility to mate. Rouse and his colleagues wondered how these newly discovered males are able to seek out a mate, given their unfettered independence.
The evolutionary solution? Make the male’s body extremely extendable, some 10-times its contracted state, so he can reach far out to find female counterparts. In fact, Rouse found that the entire body of the new species has evolved as a tool for mating. “That’s why we named it Osedax priapus,” says Rouse, “after the Greek/Roman god of fertility.”
New maps and deep seeps
Beyond bizarre animals, Scripps researchers are defining new boundaries of the deep sea, in the most literal sense.
Lead scientist David Sandwell and his colleagues tapped into new streams of satellite gravity measurements as well as shipboard sonar for a new, unprecedented depiction of the entire world’s seafloor. The most detailed map of the deep ever pieced together is the visually stunning equivalent of draining all of the water from the oceans and mapping the features at the bottom with striking clarity.
The previously unseen deep ocean structures include thousands of uncharted sea mountains rising a kilometer or more from the seafloor. The new map also gives us clues about the formation of continents, furthering our understanding of the planet’s evolution.
“The kinds of things you can see very clearly now are abyssal hills, which are the most common landform on the planet,” says Sandwell. “These elongated hills reveal the direction and speed of seafloor spreading over the past 180 million years.”
Scripps researchers are not only zeroing in on details of the deep at a global scale, but right in UC San Diego’s proverbial backyard.
In 2012, Scripps graduate students led an expedition off the San Diego County coast and discovered a deep-sea site just 30 miles west of Del Mar where methane is seeping out of the seafloor, the first such finding in our region.
Such “methane seeps” are unique and fascinating environments because of their extraordinary chemical features, at times with bubbling methane streams, and often inhabited by odd and uniquely adapted creatures.
“The diversity of habitat types we saw within this one seep was really striking,” says UC San Diego alumnus Ben Grupe, SIO ’14, lead scientist of the study. “Some areas featured really dense but patchy clam beds, others had sediments covered with bacterial mats, while others had snails and carnivorous sponges living on large carbonate rocks.”
Each of these organisms employed its own adaptations to make a living at the Del Mar seep. Clams position themselves in the mud where they can breathe oxygen and absorb seeping fluids to feed their symbiotic bacteria, while sponges have adapted to the unique chemical conditions by feasting on methane-consuming microbes.
Interestingly, scientists say these methane seeps may be connected with each other across vast distances as well as with other ocean ecosystems. Because marine species produce larvae that drift on the ocean currents before maturing, any snail or worm from the Del Mar seep may have parents that live at a different methane seep, such as those near Santa Barbara, Oregon or even Costa Rica.
Stewardship of the deep
Not only are Scripps researchers intimately involved in unlocking the mysteries of extremely deep environments—including the deepest spot on the planet—but they are active participants in protecting these worlds only now coming to light.
Graduate student Natalya Gallo and biological oceanographer Lisa Levin, SIO ’82, a renowned deep-sea expert, recently announced the findings of a study that analyzed data from the Deepsea Challenge Expedition, filmmaker James Cameron’s record-setting dive to the Mariana Trench, the deepest location on Earth. On March 26, 2012, Cameron made exploration history by completing the first solo dive to the Mariana Trench’s Challenger Deep at 6.8 miles below the ocean surface.
Gallo spent more than a hundred hours poring over high-definition video footage taken from Cameron’s submersible, along with images taken with deep-sea lander instruments developed by longtime Scripps engineer Kevin Hardy.
Like the Del Mar seep, Gallo was struck—not by a lack of life at such harsh and highly pressurized depths—but by the vibrant mix of the abundant life, especially when comparing one deep-sea community with another. The trench floor ecosystems in the New Britain Trench off Papua New Guinea harbored a forest of ghostly anemones growing on the trench wall, while hundreds of small sea cucumbers, acorn worms, amphipods and annelids moved along the soft sediments of the trench floor.
A never-before-seen jellyfish was observed drifting along with the currents and feeding on the trench floor bottom, while at the entrance to the trench a newly discovered squidworm was encountered. Even further within the Mariana Trench in the Challenger Deep, the world’s deepest community of sea cucumbers was observed showing that the world’s most remote locations can still support complex life forms and robust communities.
“It’s incredible to think that life can exist in those conditions,” says Gallo. “Exploring these environments more and exploring the animals that live there may allow us to understand how they are able to function in a high-pressure environment.”
Scripps professor Doug Bartlett, who served as chief scientist of the Deepsea Challenge Expedition, says the project was unique in that it supported basic scientific exploration at a time when other funding sources were reluctant to do so.
“Because of this expedition, scientists are in a position to ask questions about the diversity, adaptations and activities of life in an environment in which the physical and chemical properties are distinct from those that operate on Earth’s surface,” says Bartlett.
As a longtime researcher and advocate of the deep and its resources, Levin believes such research provides crucial information in understanding an environment that has become increasingly threatened by human activities, especially as oil and gas exploration has moved into deeper waters and fishing activities have shifted to deep-sea species.
We humans don’t have a great track record with stewardship of land and our coastal ocean, but hopefully we can do a better job with the deep half of the planet.Lisa Levin, ’82
“Most of the deep ocean has never been explored. But what we have seen reveals a vast diversity of life forms and habitats,” says Levin. “The need to preserve deep-sea ecosystems is now urgent due to growing threats from the search for new sources of food, energy and precious materials.”
Levin started and helps lead a campaign known as the Deep Ocean Stewardship Initiative, an effort designed to bring together natural and social scientists, regulators, the private sector and civil society to provide guidance on the environmental management of the deep ocean.
“Vast tracts of deep seabed are now being leased in order to mine nodules, crusts, sulfides, and phosphates rich in elements demanded by our advanced economy,” says Levin. “We humans don’t have a great track record with stewardship of land and our coastal ocean, but hopefully we can do a better job with the deep half of the planet.”