Cary 9618007 Almost 20 years ago researchers discovered unique communities of organisms inhabiting deep-sea hydrothermal vents located along the Eastern Pacific mid-ocean spreading centers. The question of how these species disperse and maintain their populations in these patchy, ephemeral habitats has remained one of the most interesting and unanswered problems in vent ecology. This study will be part of the Larvae-at-Ridge-Vents Project (LARVE), which is a component of the ongoing Ridge Inter-Disciplinary Global Experiments (RIDGE) program. Central to the success of LARVE is understanding the way in which hydrothermal-vent species maintain populations. Results of earlier work suggest that vent species produce pelagic larvae that are responsible for colonization of new vent sites and for maintaining populations at established sites. However, available evidence is almost entirely circumstantial. The patchiness of vent fields (in time and space) compounds the problem and demands innovative solutions that use the most tractable species as models for dispersal and recruitment. The focus of the research will be the vent crab, Bythograea thermydron. This crab shares the life-history characteristics that have made decapod crustaceans the taxon-ofchoice for a great many shallow-water studies of dispersal and recruitment. The central hypothesis of the study maintains that Bythograea thermydron disperses among vent sites via demersal larvae that take advantage of both subtidal bottom currents and the well developed swimming ability of the larvae. Understanding the life histories and the biological and physical constraints on dispersal of crabs from vents sites is critical to establishing credible models of how these communities are established and maintained along mid-ocean ridges.