Biologists with the National Oceanic and Atmospheric Administration (NOAA) were locating and surveying deep water beds of corals and sponges.
They found a number of species of coral new to science and others that will have to be re-categorized.
"Right at the end of the dive we found one sponge there that was absolutely incredible. It was on maybe a three-foot stalk," said Chris Kelley, HURL program biologist.
"I saw sponges that were more than six feet tall and corals that were more than twenty feet long," Papahanaumokuakea research coordinator Cori Kane said.
They used a submersible from the Hawaii Undersea Research Laboratory (HURL) to descend a mile below the ocean surface.
"It's like shaking a tree in the Amazon," submersible pilot Max Cremer said. "Most likely no human being has ever set eyes on that particular parcel of the earth's surface."
The scientists said they've barely scratched the surface of the area.