To date, the deep-sea hydrothermal ecosystem is thought to reach 100 to 100,000 times more in animal biomass than that of ambient deep-sea; e.g., 2 to 8.5 kg wet weight m super(-2), as the standing stock of benthic macrofauna around hydrothermal vents on the northern East Pacific Rise (Gage & Tyler, 1991), compared to 0.01 to 100 g wet weight m super(-2) in the general deep-sea at depths between 1000 to 3000 m. (Rowe, 1983). Although a considerable number of benthic animals in hydrothermal regions, such as a tube-worm Riftia pachyptila Jones, 1981 and large-sized bivalves Calyptogena magnifica Boss & Turner, 1980 and Bathymodiolus thermophilus Kenk & Wilson, 1985 are known to have developed symbiotic relationships with chemoautotrophic bacteria (Gage & Tyler, 1991), free-living microorganisms must also be important as a potential food source for many suspension-feeding zooplankton and benthic animals. The southern East Pacific Rise (S-EPR) between 13o40' and 18o40'S is a representative superfast-spreading mid-ocean ridge with a full spreading rate of ca. 15 cm yr super(-1). In 1993 and 1994, we conducted Ridge Flux'93 cruises via the RN Melville, Scripps Institution of Oceanography, and MODE'94 cruises via the R/V Yokosuka, with a manned submersible, Shinkai 6500, Japan Marine Science and Technology Center, for an extensive study of the S-EPR region. |
