Studies on the Physiological Ecology of Hydrothermal Vent Chemoautotrophic Symbioses

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9632861 CHILDRESS The vent fauna is an ancient fauna of global distribution in the deep-sea. It has limited taxonomic affinities to other deep sea communities, and yet it has affinities to the faunas of deep-sea hydrocarbon seeps and other seep environments. This deep-sea vent environment may have been a refuge protecting vent taxa from the extinction events which had great impacts on other communities. Thus, deep-sea hydrothermal vents are one of the major ecosystem types on the earth, but probably the least known. The existence of these communities depends upon the ability of a few invertebrate/ bacteria symbioses to oxidize reduced chemical species (sulfide or methane) from the vents using oxidants (oxygen or nitrate) from the surrounding deep-sea water to power primary production. Thus the capacities for interaction of the symbioses with the chemical properties of vent environments is fundamental to the primary production which supports these ecosystems. The central objective of this project is to describe and quantify the chemical interactions of the tubeworm Riftia pachyptila with the vent fluids which flow over it so that these interactions can be modeled for entire assemblages of animals. This project includes development of indices of growth rate, primary production, condition, and environmental conditions based on measurements made on freshly collected worms. The project has 3 components: 1) Survey of diverse vent and seep environments to determine the responses of chemoautotrophic symbioses to widely differing conditions. The objective is to quantify a broad range of parameters on samples from freshly captured worms and to correlate these with environmental characteristics so that the in situ interactions of the worms with the vent fluids can be estimated. 2) Shipboard studies of the physiology supporting autotrophy in symbiotic vent animals. The objective of these studies is to measure the interactions of Riftia with the various chemical parameters, a s well as the effects of temperature on these interactions, to develop an understanding of the functioning of the worms. Long term maintenance of worms in pressure aquaria for growth studies is part of these projected studies. 3) The observation and measurement of temporal changes at 13 N. This includes deployment of temperature recorders to measure the variation in conditions and selected observations of the biota to describe the changes over time. The objective is to describe the niche of the tubeworm on longer time scales so that primary production and interactions with vent fluids can be estimated over longer time periods. This project will greatly increase our understanding of the nature of the interactions between the vent animals and their chemical environments, contributing to our understanding of the functioning of the vent and other chemoautotrophically supported ecosystems.