A coupled modeling and empirical approach to the study of the life history and physiological ecology of cold seep vestimentiferans and communities. Seep vestimentiferans and their symbionts are primary producers that provide complex habitat structure in a non-toxic setting for a diverse assortment of seep-endemic and non-endemic heterotrophic species. As such, they are arguably the most important keystone species in widespread areas of seepage on the continental slope. Recent work has demonstrated that one species (at least) of seep vestimentiferan is extremely long-lived and can support its autotrophic life style with the uptake of dissolved gasses across buried portions of its body. Thus, in many ways, the seep vestimentiferans are analogous to long-lived, ecosystem-structuring, woody plant species in a terrestrial environment. We will develop models to address resource acquisition and allocation, life histories, and community productivity of cold seep vestimentiferans that will guide and focus field and laboratory studies of cold seep vestimentiferan communities. We propose to work on the upper Louisiana Slope of the Gulf of Mexico at a depth range of 540 to 1,000m and will include communities on both hard substrata and sediment that are exposed to a range of sulfide concentrations. We will use empirical studies and comparative methods to develop, test the predictions of, and refine, Dynamic Energy Budget models, while at the same time addressing specific hypotheses concerning vestimentiferan aggregation physiology and ecology. Our in situ work will be guided by these mathematical models and interfaced with very efficient and quantitative collection methods that will maximize the information gleaned from each collection and provide material for future studies, thereby minimizing our short and long-term impact on the communities. Growth rates of thousands of individuals will be measured and these data used to estimate the longevity and to calculate the resources allocated to growth by each vestimentiferan species. We will determine whether "roots" (posterior extensions that can be used to mine sulfide from within sediments) are a general feature of seep vestimentiferans and whether they are environmentally induced. The models will be used to explore the relative importance of root sulfide uptake to the sustenance of aggregations in different situations and the implications of vestimentiferan sulfide demand on biogeochemical models of sulfide production. To facilitate this, environmental concentrations of sulfide and diffusion distances across root tubes and tissues will be measured, and concentrations and sulfide binding properties of the hemoglobins in the different species will be determined. The biomass, size frequency, distribution, and reproductive state of the vestimentiferans will be determined for intact aggregations and collections processed so that the species richness and biomass of all associated fauna in each collection can also be determined. This will allow us to formulate life history models, to scale up the models of individuals to the levels of aggregations, and to model excess production and its use by associated fauna. Fisher has extensive experience with the Gulf of Mexico seep communities and has visited the sites. Shea is a theoretical ecologist with experience in life-history modeling of terrestrial and aquatic autotrophic systems. The proposed approach will significantly increase our understanding of these widespread and productive deep-sea communities and their impact on the surrounding deep sea, and will provide a modeling framework to focus related and future investigations. The proposed studies will yield basic insights on the ecology, physiology and reproductive biology of deep-sea systems in general and chemoautotrophic systems in particular. They will also provide new theory, and tests for existing theory on the evolution of life history strategies.