White Paper Title: 
Carbon assimilation at hydrothermal vents: Quantitative linkages between biotic responses to physico-chemical fluid conditions.

C. Meile1 and P. Girguis2

1University of Georgia, Department of Marine Sciences, Athens, GA 30602
2Harvard University, Department of Organismic & Evolutionary Biology, Cambridge, MA 02138

Abstract: Hydrothermal vents host a diverse and productive biotic community, ultimately supported by the difference of composition between the rising fluid and ocean water. However, the quantitative relationship between fluid characteristics and the physiological response in terms of carbon uptake of key organismal groups such as tubeworms, microbial mats and mussels remains poorly constrained. Our ongoing work aims at establishing such explicit quantitative connections, by linking respirometer measurements of tubeworms, in particular Riftia, and mussels performed under in situ pressure to the geochemical milieu. We are exploring the relationship between environmental factors and biotic response based on a set of laboratory experiments performed at known physico-chemical conditions, in which a single environmental parameter was varied (Girguis and Childress 2006, J. Exp. Biol. 209: 3516-3528). These relationships are then embedded into a mathematical framework that accounts for known buffer capacities of a group of organisms, e.g. for the capability of tubeworms to continue carbon-uptake over an extended period of time even after the delivery of new sulfide has stopped. As a next step, organismal densities then inform the population specific assimilation rates, which vary with environmental conditions that can be measured transiently and in situ (Govenar et al. 2005, MEPS 305: 67-77).

Contributions to Integration and Synthesis: Studies on composition and metabolic capacity of the megafaunal and microbial denizens of hydrothermal vents have been complemented by chemical studies that seek to correlate fluid chemistry with vent biota. However, little is known about the net rates of biogeochemical processes, e.g. primary productivity, in these surficial communities and the above mentioned work contributes to closing this gap. Moreover, distribution and relative importance of the subsurface processes that produce the observed biological assemblage are still not well constrained. Hence, our estimates of fluid controlled net primary production will be interfaced with the work sponsored through a Ridge2000 Postdoctoral Fellowship to B. Larson, which aims at establishing the spatial context for variations in fluid conditions via reactive transport modeling at the Main Endeavour Field site.