Boiling hydrothermal vents and areas where cold methane seeps from the ocean floor exist together, researchers said, in areas they've dubbed hydrothermal seeps.
Writing in the journal Proceedings of the Royal Society B: Biological Sciences, researchers described a large number of previously unknown deep-sea species that have adapted to the hybrid environments.
"The discovery shows that we still have much to learn about hydrothermal vents and methane seeps and about the vast depths of the oceans," said David Garrison, director of the National Science Foundation's Biological Oceanography Program, which funded the research led by the Scripps Institution of Oceanography in La Jolla, Calif.
"We need to re-think the boundary," he said, "of where a vent begins or a seep ends."
The most interesting aspects of the site, Scripps researcher Lisa Levin said, "are the presence of vent-like and seep-like features together, a vast cover of tubeworms across large areas, and a wealth of new species."
In addition to tube worms, the researchers found deep-sea fish, mussels, clam beds and high densities of crabs.
It's possible other hybrid or "mosaic" ecosystems remain undiscovered with marine life specialized to live in such environments, the researchers said.
"Plenty of surprises are left in the deep sea," Levin said. "There are new species, and almost certainly new ecosystems, hidden in the oceans."
2014: The Year in Music [PHOTOS]