摘要：

The phenomenon of hydrothermal venting is a product of the deep-earth processes that drive plate tectonics and the genesis of ocean crust at spreading centres. Trapped sea water circulates below the crust and emerges near spreading axes as heated fluids with many dissolved substances derived from the lower rocks. It is the presence of dissolved sulphide ions that is responsible for the formation of polymetallic sulphide deposits and of unusual animal communities in which chemosynthetic microbes produce organic carbon. The best known vent sites are those on the Galapagos Rift, the East Pacific Rise and in the northeast Pacific. Recent discoveries include vents at back-arc spreading centres in the western Pacific and on the Mid-Atlantic Ridge. Chemoautolithotrophic bacteria form the base of the trophic structure at vent communities in at least four pathways: in the emergent plume that disperses over large distances, in local particulates used by vent suspension-feeders, in the microbial mats consumed by grazers and in symbiotic association with macro-invertebrates. The vent macrofauna is now known to have 236 species, of which 223 are new to science. The fauna is endemic and taxonomically distinct from that of the normal deep-sea. Faunal biomass is several orders of magnitude higher than that of the deep-sea although diversity is markedly low. Little is known about the biology of most vent species although the more spectacular animals have received attention. Several features of reproduction and growth of the vent tube-worms, bivalves, polychaetes, and crabs have been studied for clues to larval dispersal and recruitment; no vent-specific pattern is recognised. Variations in vent outflow and in fluid chemistry may cause much local heterogeneity. Distinct groups of organisms can be identified in relation to venting vigour and the supply of dissolved sulphides. Competition for such fluids may alter the aspect of an assemblage over time. The requirement for mutually exclusive oxygen and sulphide molecules in symbiont-hosts has fostered adaptations for spatial separation of uptake sites or for temporal separation as local turbulence induces fluctuations in dissolved concentrations. It is likely that any one vent field exists for decades during which time several generations may establish, but development of field-specific adaptations will not occur. Substantial changes in biota have been witnessed at several vents in which both geological and biological agents have been implicated. Vent fields may be separated by tens to hundreds of kilometres while magmatic processes controlling rifting may separate vent sites over many ridge segments. Faunal composition over large distances is not predictable and may relate to larval dispersal and chance recruitment. The vent fauna may have several origins including the adjacent deep-sea, shallow water and a pool of opportunistic sulphide-exploiters. But most vent animals have no extant close relatives and represent new taxonomic levels above the genus. Several taxa suggest a great antiquity and that evolutionary divergence of much of the assemblage may have occurred in the Mesozoic. Biogeographic work in concert with study of tectonic history suggests that geology has a tight control on the modern features of vent communities especially when considering Cenozoic plate patterns. Information on evolution of vent fauna from paleontological evidence is sparse but, late Palaeozoic assemblages are described. The only constraint on the invasion of this rich habitat by megafauna is the availability of dissolved oxygen in the deep-sea. Whether or not life originated at vents in the Archaean is debatable, but hydrothermal conditions probably supported chemosynthetic microbes early in their evolution.

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