Cooperative Research: Studies on the Physiological Ecology of Hydrothermal Vent Chemoatotrophic Symbioses

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Vent fauna is a largely ancient fauna of global distribution in the deep?sea. It has limited taxonomic affinities to most deep?sea communities, and yet it has affinities to the faunas of deep?sea hydrocarbon seeps and other seep environments. Deep?sea hydrothermal vents are one of the major ecosystem types on the earth, but probably the least known. The high biomasses of these communities largely reflect the ability of a few invertebrate/bacteria symbioses to oxidize reduced chemical species (sulfide or methane) from the vents using oxygen from the surrounding deep?sea water to power primary production. The allegation that vent communities are highly productive is often seen in the literature based on the high biomasses estimated, the rapid establishment of vent communities and the rapid growth of some vent animals. However, there are currently no well?founded estimates of primary production by the symbioses at any hydrothermal vents. The central objective of this study is to quantify the major vent symbioses' chemical interactions with the vent fluids and the abundances of those symbioses in such a way that primary and secondary production and other chemical exchanges can be modeled for entire assemblages of symbiotic animals. This involves determining the range of production and exchange rates of the symbioses and the relations between environmental conditions and those rates. Environmental data will then be used to estimate in situ rates for entire assemblages at single points in time and over the lifetime of vent sites. This consists first of the Childress group expanding its study of the rates of exchanges to a range of sizes of all the major autotrophic symbioses. Complementing this, the Fisher group will characterize and sample sites at 9'50'N on the EPR so that the biomass, organism abundance and organism sizes are documented and size/weight relationships are developed. These data will enable the estimating of production in entire symbiotic assemblages and they can also be used with existing photographic datasets to estimate biomasses at other EPR sites which have been photographically documented and for which chemical datasets exist. The results will greatly increase the understanding of the nature of the interactions between the vent animals and their chemical environments and enable the first solid estimates of production and other exchanges by the symbiotic components of vent communities, making a major contribution to the understanding of the functioning of vent and other chemoautotrophically supported ecosystems.