LARVAE OF BENTHIC INVERTEBRATES IN HYDROTHERMAL VENT PLUMES OVER JUAN-DE-FUCA RIDGE

Larvae of benthic invertebrates collected in the water column above Ju an de Fuca Ridge show distinct variations in abundance and composition in, and away from, the neutrally-buoyant hydrothermal plume emanating from underlying vents. Larvae of vent gastropods (Lepetodrilus sp. an d two peltospirid species) occur in significantly higher abundances in the plume than away from it (mean abundance = 21.0 individuals 1000 m (-3) vs 1.4 individuals 1000 m(-3)), and larvae of vent bivalves (Caly ptogena? sp.) occur exclusively in the plume (mean abundance = 0.5 ind ividuals 1000 m(-3)). Larvae from other benthic taxa known not to be e ndemic to Juan de Fuca vent communities, such as anthozoans, pholad cl ams, bryozoans and echinoderms, are less abundant in the plume than aw ay (mean abundance = 47.5 vs 16.9 individuals 1000 m(-3)) at comparabl e depths and heights above the bottom. These results support the hypot hesis that larvae of vent species are entrained into buoyant hydrother mal plumes and transported at the level of lateral spreading, several hundred meters above the seafloor. The discovery of vent-associated la rvae in the plume suggests that models used to predict hydrodynamic pr ocesses in the plume will also be useful for modeling larval dispersal . Advanced imaging and new molecular-based approaches will be required to resolve taxonomic uncertainties in some larval groups (e.g. certai n polychaete families) in order to distinguish vent species and make c omprehensive flux estimates of all vent larvae in the neutrally-buoyan t plume.