Testing biological control of colonization by vestimentiferan tubeworms at deep-sea hydrothermal vents (East Pacific Rise, 9°50′N)

Three species of vestimentiferans are found at hydrothermal vents on the East Pacific Rise (EPR). Tevnia jerichonana is an early colonist and Riftia pachyptila has the greatest biomass in established vent assemblages, but the role of Oasisia alvinae, a small species that occurs sporadically, is unknown. Anecdotal evidence suggests that O. alvinae may be abundant in the microhabitat underneath mussels. Previous studies have suggested that early T. jerichonana colonists may facilitate settlement of the late colonist R. pachyptila. To address potential mechanisms for the successional sequence and to explore the role of O. alvinae, we examined the effects of the presence of vestimentiferan (R. pachyptila and T. jerichonana) tubes and mussel (Bathymodiolus thermophilis) shell cover on recruitment of vestimentiferans on basalt blocks deployed at 9°50′N, 104°17′W on the EPR. A molecular assay was used to identify individuals to species since they were too small to be identified morphologically. Although colonists in both experiments belonged to all three species of vestimentiferans, only a few were T. jerichonana. Colonization of vestimentiferans did not increase in the presence of vestimentiferan tubes. The presence of mussel shell cover did not influence the proportions of R. pachyptila and O. alvinae, or the total number of colonists. Because the experimental blocks in this study were placed within dense clumps of R. pachyptila, we suggest that, while T. jerichonana may be an important cue for vestimentiferans settling at new vents, adult R. pachyptila also can act as a settlement cue for larvae. O. alvinae colonists were abundant in all of the treatments in our experiments, indicating that, although adults of this species are apparently rare at these sites, O. alvinae can settle in abundance if a suitable micro-environment is available.