Published online by Cambridge University Press: 06 July 2010
Despite the importance of early life-history processes in regulating population assemblages of benthic invertebrates at hydrothermal vents, they remain poorly understood, mainly because of the inaccessibility of these habitats. Vestimentiferan tubeworms provide an excellent system to study settlement in these habitats; they inhabit tubes that remain intact for some period even after the occupants die, and thus provide a proxy for rates of settlement and post-settlement mortality. In 2007, we collected rocks supporting populations of Lamellibrachia sp. using a TV-grab, from Mussel Ridge hydrothermal vent field on Monowai Volcanic Complex, at the Tonga–Kermadec arc. Twenty-two discrete patches of similarly sized individuals and of discrete length–frequency distributions were identified and quantified. Mean length of individual tubeworms ranged from <0.5 to 6.38 cm, and abundance per patch ranged from 6.8 to 108 ind cm−2. Post-settlement mortality was ~5%. These results suggest that gregarious settlement of pulses of larvae is likely occurring by Lamellibrachia sp., a process that has not yet been described in deep-sea hydrothermal vent tubeworms. The abundance of adult tubeworms on Monowai was low, and allochthonous larval supply from neighbouring seamounts unlikely. Consequently, gregarious settlement can increase the probability of maintenance and expansion of the existing populations.