Composition of a One-Year-Old Riftia pachyptila Community Following a Clearance Experiment: Insight to Succession Patterns at Deep-Sea Hydrothermal Vents

Abstract

In the basalt-hosted hydrothermal vent habitat around 9°50 N on the East Pacific Rise, the vestimentiferan tubeworms Tevnia jerichonana and Riftia pachyptila (Polychaeta: Siboglinidae) commonly settle before the mussel Bathymodiolus thermophilus (Bivalvia: Mytilidae). We removed six aggregations of R. pachyptila and deployed mussels on the cleared sources of diffuse flow to test the effect of the B. thermophilus on the subsequent colonization by the tubeworms. None of the transplanted mussels persisted on the cleared sources of diffuse flow; however, aggregations of R. pachyptila grew in half of the clearances. We collected one of the aggregations of R. pachyptila along with the associated fauna for determination of relative abundance and biomass in this one-year-old community. This aggregation consisted of 647 specimens of R. pachyptila that hosted individuals of 24 species, including small individuals of T. jerichonana and B. thermophilus. The abundance of the associated fauna was numerically dominated by gastropods, and the biomass was dominated by the Alvinellid polychaete Paralvinella grasslei. Following an eruption, the vestimentiferan tubeworms Tevnia jerichonana and Riftia pachyptila (Polychaeta: Siboglinidae) quickly colonize the basalt-hosted hydrothermal vents around 9°50 N (East Pacific Rise) and soon grow to visually dominate these habitats (1, 2, 3). Colonization by the vent mussel Bathymodiolus thermophilus often follows shortly, and the mussels eventually overgrow the tubeworms at most sites (2, 4, 5). Both tubeworms and mussels harbor sulfur-oxidizing chemoautotrophic endosymbionts, which provide the bulk of their nutrition (6, 7). However, mussels have also maintained the ability to filter-feed (8), which apparently allows them to occupy a wider range of environmental conditions and better tolerate declining hydrothermal vent activity than the tubeworms (9). The mechanism of ecological succession in these hydrothermal vent habitats is not fully understood, but may be regulated by a combination of pre-settlement factors, such as the use of biogenic cues (3) and the response to geochemical changes (2), and post-settlement factors, such as physical overgrowth (4) and resource competition (5). We conducted a manipulative experiment to test the hypothesis that the mussel B. thermophilus prevents further colonization of a vent by tubeworms. In May 1998, six aggregations of the giant tubeworm R. pachyptila were cleared from a site named Riftia Field (9°50.705 N 104°17.593 W). The original location and source of diffuse flow for each aggregation were marked and recorded on video. After the aggregations were cleared, the temperatures of the venting fluid were measured, using the low-temperature probe of the DSV Alvin, and ranged from 20–22 °C above ambient at the six locations. Then about 600 mussels were collected from a nearby site (“East Wall”, 9°50.614 N 104° 17.509 W) and about 200 were deployed over each of three cleared sources of diffuse flow (treatments). Mussels were not deployed on the three other cleared areas (conReceived 28 April 2004; accepted 4 October 2004. * To whom correspondence should be addressed. E-mail: breea@psu.edu † Present address: Department of Fisheries and Aquatic Sciences, University of Florida, Gainesville, FL 32653. Reference: Biol. Bull. 207: 177–182. (December 2004) © 2004 Marine Biological Laboratory