Ocean-ridge segmentation and vent tubeworms (Vestimentifera) in the NE Pacific

Abstract Vestimentiferan tube worms are important components of the hydrothermal vent and cold seep communities of the Pacific Ocean. The distribution and geographic intraspecies variation of Ridgeia piscesae and Lamellibrachia barhami were examined in the region of the Explorer (1 site), Juan de Fuca (33 sites) and Gorda (2 sites) Ridges and the nearby Cascadia Subduction zone. Isozyme electrophoresis, DNA restriction fragment length polymorphism (RFLP) and DNA sequencing techniques have been used. Ridgeia piscesae is widespread at hot vent sites along the ridges. The transform offset between Explorer and Juan de Fuca does not appear to impede gene flow (isozyme and RFLP data). Hydrographic conditions close to the Juan de Fuca Ridge favour bidirectional along-axis transport of planktonic larvae and some cross-axis transport. Rapid colonization by R. piscesae has been observed at a new vent site on CoAxial Segment of the Juan de Fuca Ridge, supporting the idea of a pool of larvae in the water overlying the ridge. The 360 km offset between southern Juan de Fuca and Gorda Ridges is associated with a significant level of genetic differentiation (shown by RFLP) which indicates some interruption to larval dispersal at this scale. The occurrence of the cold-seep species Lamellibrachia barhami is confirmed at one hydrothermal site, the sedimented Middle Valley on Juan de Fuca Ridge. Vestimentiferans appear to have a tremendous dispersal, location and adaptation capability. It is only at the thousand kilometre scale, that complete barriers to dispersal occur.