Microbial populations at deep-sea hydrothermal vents link the transfer of geothermal energy to the production of organic carbon, known as chemosynthesis. As the particulate organic food source for the filter-feeding and grazing vents animals, free-living bacteria function as the chemosynthetic base of the food chain for this part of the vent communities. During the continuation of the RIDGE Initiative, this project will focus on those bacteria from hydrothermal vents. Dr. Jannasch will address the question - which chemosynthetic bacteria are quantitatively the most important in terms of productivity at hydrothermal vents? To answer this question, newly-developed techniques will be used to assess aerobic and anaerobic chemosynthetic bacteria at a large variety of vent environments. Rates of growth and chemosynthesis will be measured by a variety of in situ and laboratory experiments. It's assumed that these natural microbial populations are highly responsive to environmental conditions and, therefore, representative of temporal geophysical-geochemical changes of vent systems. Work at the Mid- Atlantic Ridge vent sites will deal with new approaches for in situ rate measurements of chemosynthetic activity by microbial populations covering the polymetal sulfide deposits. In addition, work is also planned for the Guaymas Basin Beggiatoa mats. These studies will involve the use of two submersibles, the ALVIN and JASON/MEDEA.//
