Microbial Population and Chemosynthetic Primary Production in Hydrothermal Plume along the Southern East Pacific Rise
Akihiko MARUYAMA*a, Tetsuro URABEb, Junichiro ISHIBASHIc, Richard A. FEELYd, and Edward T. BAKERd
a Applied and Environmental Microbiology, National Institute of Bioscience and Human- Technology, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan
b Geological Survey of Japan, 1-1 Higashi, Tsukuba, Ibaraki 305, Japan
c Faculty of Science, U. of Tokyo, 1-1-1 Yayoi, Bunkyo, Tokyo 113, Japan
d Pacific Marine Environment Laboratory, National Oceanic and Atmospheric Administration, Sand Point Way N.E., Seattle, WA 98115-0070, U.S.A
A dense microbial population was detected extensively in hydrothermal plumes along the southern East Pacific Rise (S-EPR) between 13°40' and 18°40'S. The population shows an excellent correlation with hydrothermal parameters such as nephelometer intensity, particulate sulfur and methane concentration, particularly over the ridge crest south of 17ー20'S, where many plumes rich in volatile gases were detected. At several stations, however, maximum cell density is found at the hydrothermal plume's upper and lower boundaries, not at the center. Plume layers at 2,300 to 2,600 m in depth were also characterized by the dominance of coccus microbes, while the rod-shaped microbes increased downward to seafloor venting sites, ca. 2,600-2,700 m. Using geochemical and geophysical parameters such as an excess amount of particulate carbon, water volume in the plume and mean plume velocity, total chemosynthetic net primary production (CNPP) is estimated at ca. 3.3 x 108 kg yr-1 for the S-EPR. Applying mean spreading rate in the global ridge system, oceanic CNPP is finally estimated at 0.1 to 1% of total photosynthetic net primary production in the ocean. This hydrothermal new production reaches to 1 to 25% of total downward carbon flow from the ocean surface. The contribution of hydrothermal primary production should be amplified more than this estimates in the vicinity of worldwide ridge environments. In hydrothermal fluids collected by a submersible, Shinkai 6500, many microbes and microbe-like filamentous particles were detected. Portions of near-vent microbes in the S-EPR appear likely to originate in a subsurface biosphere beneath the seafloor, especially with the concentration ranges of 0.3 to 30μM in dissolved Mn and/or 1 to 100μM in H2S.
