The natural instability of hydrothermal vents creates variable environmental conditions among habitat patches. Habitat differences correspond to phenotypic variation in Ridgeia piscesae, the only ‘vent tubeworm’ on the spreading ridges of the Northeast Pacific. Ridgeia piscesae that occupy high fluid flux habitats have rapid growth rates and high reproductive output compared to tubeworms in habitats with low rates of venting fluid delivery. As recruitment occurs in all settings, worms in the “optimal habitat” may act as source populations for all habitat types. Ridgeia piscesae is a foundation species in the Endeavour Hydrothermal Vents Marine Protected Area of the Juan de Fuca Ridge. The objective of this thesis was to assess fine scale population structure in Ridgeia piscesae within the Endeavour vent system using genetic data. Population structure was assessed by analysis of the mitochondrial COI gene in 498 individuals collected from three vent sites of the Juan de Fuca Ridge; Middle Valley (n=26), Endeavour Segment (n=444) and Axial Volcano (n=28). Genotyping using microsatellite markers was attempted but all loci developed for closely related tubeworm species failed to amplify microsatellites in Ridgeia piscesae. Sequence analysis identified 32 mitochondrial COI haplotypes; one dominant haplotype (68%), three common haplotypes (4%-7%) and the remainder were rare (<2%). Axial Volcano was differentiated from Middle Valley and Endeavour. Within Endeavour, genetic sub-structuring of Ridgeia piscesae occurred among vent fields (Clam Bed, Main Endeavour and Mothra) and habitat types < 10 km apart. Patterns of genetic variation and coalescent based models suggested that gene flow among vent fields moved in a north to south direction in individuals from high flux habitat but from south to north in individuals from low flux habitat. Tubeworms from low flux habitat had more nucleotide polymorphisms and haplotypes than those from high flux habitats. Estimates of the number of immigrants per generation moving from high flux to low flux subpopulations was four times higher than in the reverse direction. The effective population size was estimated to be three times greater in high flux habitat when the generation times for individuals from each habitat type were considered. Demographic tests for population equilibrium identified a recent and rapidly expanding metapopulation at Endeavour. Models of gene flow in Ridgeia piscesae reflected the general oceanographic circulation described at Endeavour. Genetic data illustrate that dispersing larvae exploit the bi-directional currents created through plume driven circulation within the Endeavour axial valley and suggest that adult position on or near chimneys may influence larval dispersal trajectories upon release. Building on known ecological and biological features, this study also showed that Ridgeia piscesae from limited and ephemeral high flux habitat act as sources to the overall metapopulation and that asymmetrical migration and habitat stability sustain high genetic diversity in low flux sinks. The overall metapopulation at Endeavour experiences frequent extinction and recolonization events, differences in individual reproductive success, and source-sink dynamics that decrease the overall effective size and genetic diversity within the population. These factors have important implications for the conservation of a foundation species. / Graduate / 0307 / 0329 / 0369 / lcpuetz@uvic.ca

Prokaryotic microorganisms, which are at the base of deep-sea hydrothermal vent food webs, adapt rapidly to environmental fluctuations. This study aimed at comparing bacterial communities in contrasting hydrothermal habitats to better understand compositional adaptations to local conditions. I first used small subunit (SSU) ribosomal RNA (rRNA) gene sequences to compare mat-forming bacterial communities associated with iron oxides at two hydrothermal vent sites on the Tonga Arc, southwest Pacific. Operational taxonomic units (OTUs), defined at 97% sequence similarity, were affiliated to a great diversity of autotrophic and heterotrophic groups. Metabolically diverse Gammaproteobacteria dominated the sample from Volcano 19, collected at 992 m depth. The sample from Volcano 1, collected at 197 m depth, was dominated by iron-oxidizing bacteria from the class Zetaproteobacteria. The depth of the sampling sites was proposed to explain clone library dissimilarities. In the following studies, I compared bacterial communities associated with the vestimentiferan tubeworm Ridgeia piscesae, a foundation species at the Juan de Fuca Ridge. Samples of the polychaete were collected from tubeworm habitats in contrasting flow regimes that influenced temperature and hydrogen sulphide concentrations. Free-living bacteria were analyzed using both sequencing and 454 pyrosequencing of the SSU rRNA gene. Statistical analyses suggested a predictable pattern of bacterial community composition for the two habitats, with higher proportions of sulphur and hydrogen oxidizers in High Flow and more heterotrophic groups in Low Flow environments. Temperature, available energy for metabolism, and stability of the habitat were suggested to explain these distinctive bacterial communities. Symbiotic assemblages were investigated using the same sequencing methods together with catalyzed reporter deposition-fluorescence in situ hybridization (CARD-FISH). Gammaproteobacteria dominated all sequence libraries, followed by Epsilonproteobacteria. CARD-FISH confirmed the co-occurrence of these groups within R. piscesae trophosomes. Statistical analyses indicated distinctive membership and structure of trophosome assemblages between sampling sites. Analysis of R. piscesae juvenile showed distinctive structural properties when compared to adult individuals, but similar membership, within sampling sites. These results suggested that the composition of trophosome assemblages might be affected by specific physical and chemical conditions at each vent site and that a selection process might occur during R. piscesae’s development. / Graduate / 0410 / 0416 / 0329 / nathalieforget@gmail.com