Factors affecting the epifaunal community associated with Riftia pachyptila at deep-sea hydrothermal vents on the East Pacific Rise

Low-temperature hydrothermal vents host dense communities of large invertebrates that obtain their nutrition exclusively or primarily through symbioses with internal chemoautotrophic bacteria. The habitat provided by these foundation species supports diverse assemblages of smaller heterotrophic invertebrates. This dissertation consists of five chapters that characterize the ecology of hydrothermal vent communities associated with the giant vestimentiferan tubeworm Riftia pachyptila (Polychaeta: Siboglinidae) at the East Pacific Rise. The first chapter reviews the literature on the physical environment, the biology of the dominant species, and the patterns and dynamics of hydrothermal vent communities. The second chapter presents the results of a clearance and transplant experiment, designed to test the role of biological interactions in the succession of low-temperature hydrothermal vents. The unexpected results provide an opportunity to characterize the patterns of recruitment and community assembly associated with an aggregation of R. pachyptila that developed in less than one year. The third chapter examines the spatial and temporal variability of the R. pachyptila community, sampled at two discrete sites and in two consecutive years. Although the temperature ranges did not vary between sites or years, the chemical composition of the diffuse hydrothermal fluids was significantly different at each site. The physiological condition of the R. pachyptila individuals appeared to reflect the environmental conditions, but the structure and the composition of the community was remarkably similar between sites and years. The fourth chapter tests the hypothesis that the physical structure of R. pachyptila aggregations supports high local species diversity in a high productivity habitat. The results of deploying artificial tubeworm aggregations along a productivity gradient for one year demonstrate the importance of physical structure, productivity and biological attributes of foundation species in the regulation of the epifaunal community structure. A summary of this work is discussed in the fifth chapter, integrating the results of quantitative sampling and experimental manipulations to investigate the roles of environmental variability, productivity, habitat provision and modification, and biological interactions in the structure of the epifaunal community associated with R. pachyptila.