LARVAL DISPERSAL VIA ENTRAINMENT INTO HYDROTHERMAL VENT PLUMES

One of the most intriguing ecological questions remaining unanswered about hydrothermal vents is how vent organisms disperse and persist. Because vent species are generally endemic and their habitat is patchy and ephemeral on time scales as short as decades, they must disperse frequently, presumably in a planktonic larval stage. We suggest that dispersal occurs not only in near-bottom currents but also several hundred meters above the seafloor at the level of the laterally spreading hydrothermal plumes. Using a standard buoyant plume model and observed larval abundances near hydrothermal vents at 9-degrees 50'N along the East Pacific Rise, we estimate a mean vertical flux of approximately 100 vent larvae/h at a single black smoker. Larval abundances were extremely variable near vents, resulting in a range in estimated fluxes of at least an order of magnitude. The suitability of the plume model for these calculations was determined by releasing dyes (fluorescein and rhodamine) as larval mimics into a black smoker plume. The plume model predicted dye fluxes in the plume adequately, given the short averaging times of our measurements and the difficulty of sampling the plume centerline. Our calculations of substantial numbers of vent larvae entrained into the plume support the idea that transport in the lateral plume is an important mechanism of dispersal. Because vertical shear in flows above vents can cause larval dispersal trajectories in the plume to deviate considerably from those along the seafloor, larvae in the plume may have access to habitats that are unreachable by larvae in near-bottom flows.