Archaea, one of three separate domains of life on our planet, were undiscovered until 1970. Since then, they had been found mostly in extreme environments such as high-temperature volcanic vents on the ocean floor, continental hot springs and fumeroles, and highly salty or acidic waters. Now, scientists funded by the National Science Foundation (NSF) have found unexpected, astounding numbers of archaea living in Earth's largest biome, the open sea.
The researchers--David Karl and Markus Karner of the University of Hawaii, and Edward DeLong of the Monterey Bay Aquarium Research Institute--have published a paper in this week's issue of the journal Nature on their discovery: "Archaeal dominance in the mesopelagic zone of the Pacific Ocean." The concentration of archaea in their study leads the scientists to conclude that archaea are "a large percentage of the biomass of the open ocean," says Karl. "These organisms could make up 50 percent of life in the open sea." The research is the first to note their numerical abundance.
"This remarkable new insight will have a major impact on our view of how the oceans function ecologically, "says Phil Taylor, director of NSF's biological oceanography program, which, along with NSF's chemical oceanography program, funded the research. "We are compelled by this discovery to increase our efforts to understand the diversity of life in the oceans, and the specific roles that important species and groups play in the sea."
The research is part of the Hawaii Ocean Time-series (HOT) project, an NSF-sponsored study of the north Pacific Ocean. Monthly sampling was conducted throughout the water column, from the surface to 4,750 meters deep. Two specific archaeal groups-pelagic euryarchaeota and pelagic crenarchaeota--were found in high numbers in the samples.
In the past, archaea were known as archaebacteria, but it has since been found that they are fundamentally distinct from true bacteria. Very little is known about these life forms. According to Karl, they were only discovered because of "their unusual genetic and molecular structures." Marine scientists have yet to understand how archaea take in nutrients, multiply, or what ecological role they play.
The habitat range for these archaea, the Nature paper authors note, is unusually broad. "As a dominant component of the ocean, archaea are thus far from confined to extreme niche habitats," they write. "Rather, the distribution of these archaea suggests that a common adaptive strategy has allowed them to radiate throughout nearly the entire water column."
The discovery of these numbers of a group of microorganisms living in a previously unsampled area "points out the basic ignorance we have of the planet we live on," maintains Karl. This research, he says, further reveals the need for a reclassification of the characteristics of the archaea kingdom.