Despite their ubiquitous distribution in tectonically active coastal zones, shallow-water
vents have been much less explored than deep-sea vents in terms of biodiversity and adaptations to
extreme conditions. We investigated the meiofaunal biodiversity and environmental variables at distances
of 10, 100 and 200 cm from a shallow-water hydrothermal vent in the equatorial Pacific
(Sulawesi, Indonesia). Meiofaunal abundance and the richness of higher taxa increased from the site
of fluid-vent emission (where temperatures of the fluids and sediments reached approximately 90°C)
to the control sediments (200 cm from the vent, with no sign of effects from the vent fluids). Nematode
species richness was also high in the intermediate station, where bottom sediment temperature
reached 55°C. These data suggest that some nematode species were able to survive in conditions
typically hostile to metazoan life. Gas emissions also influenced the biochemical composition of the
sediment organic matter in proximity to the vent and favoured the growth of a large photo- and/or
chemo-autotrophic prokaryotic biomass. This biomass represented a potentially important food
source for predator/omnivore nematodes and influenced the trophic structure of benthic assemblages.
Since the metazoan species found in proximity to the vent were a subset of those inhabiting
control sediments, but were characterised by lower abundances, it might be hypothesized that the
populations close to the vent are the result of colonization from adjacent areas.