Scientists plunged more than 6,500 feet in the submarine Alvin to investigate the underwater communities that thrive among methane gas bubbles and seeping hydrogen sulfide in the Gulf of Mexico. Activated floodlights revealed the mysterious creatures living in one of the most extreme environments on Earth-cold seeps.
As scientists peered through a tiny porthole to the ocean’s abyss, they wondered: How did these animals get here?
In May and June, 2014, researchers at NC State, Duke University, and the University of Oregon ventured out in to the Gulf of Mexico on the R/V Atlantis, the 274-foot research vessel home to the deep-sea submersible Alvin. The three universities banded together-each equipped with a unique skill set-on a mission to understand the interconnectedness of cold-seep communities there, Barbados, and along the US East Coast.
Cold seeps have a typical deep-sea temperature of 35 to 39 degrees Fahrenheit and leak gases fom the seafloor. Hydrogen sulfide and methane ooze and bubble, providing chemical food to bacteria that live in the sediment and inside the guts of animals such as worms and clams.
Cold seeps are scattered like islands across the ocean floor. They appear disconnected, but ocean currents carry larval spawn to seeps near and far. Even though seeps are some of the largest and most abundant geologic features on the planet, scientists are just beginning to understand how these communities are colonized.
Researchers from the three universities partnered to study cold-seep communities as part of a multi-year project funded by the National Science Foundation. “It was like getting the A-team together,” said Cindy Van Dover, the lead scientist on the project. She’s a biology professor and director of the Duke University Marine Lab.
David Eggleston, NC State biologist and Director of the Center for Marine Sciences and Technology (CMAST), and NC State physical oceanographer Roy He brought expertise on the movement of marine larvae and ocean currents.
The collaboration allowed scientists to compare results and synthesize their information to form a more holistic study of cold-seep communities.
NC State graduate student Doreen McVeigh is building a particle-tracking model to simulate the movement of larvae. Her model predictions are compared against genetic information to see if they match up. These tools reveal whether cold-seep “island” populations are isolated or connected.
Scientists deployed larval traps, plankton nets, and hydrophones on mooring lines anchored to the sea floor by train wheel weights to collect their data. The most advanced technologies on the ship were the submarine Alvin and the unmanned remotely-operated vehicle Sentry. Sentry used sonar to map the seafloor and target areas for Alvin to explore. “This was a tremendous asset,” said Eggleston. “We can have maps of targets in hand before going down in the submarine.”
Guided by Sentry’s map, Eggleston directed Alvin to a deep-sea brine lake surrounded by mussels, a location not seen since the late 1990s. The close proximity to the brine pool of mussels suggests that they are consuming bacteria seeping from the pool, an exciting find for the scientists. Alvin’s large robotic arm collected specimens and captured video footage of the sea-floor teaming with mussel beds, 150-year-old tube worm forests, bizarre fish and a type of sea cucumber called the headless deep-sea chicken. Calm seas enabled Alvin to complete all of its scheduled dives, giving more students the opportunity to direct an expedition.
The team collected and deployed large moorings equipped with time-release larval traps, current meters, and sound-recording hydrophones. These hydrophones recorded the sounds of deep-sea life for the first time. Traveling larvae may use sound to find the right habitat to live.
In the ship’s laboratory, scientists identified specimens, studied their behavior, and preserved samples for genetic analysis.
“By studying how these organisms are adapted to extreme environments,” Van Dover said, “we can learn a lot about the diversity of life.”