Tommy S. Moore

Interrelationships Between Vent Fluid Chemistry, Temperature, Seismic Activity, and Biological Community Structure at a Mussel-Dominated, Deep-Sea Hydrothermal Vent Along the East Pacific Rise

Abstract In April 1991, submarine volcanic eruptions initiated the formation of numerous hydrothermal vents between 9°45′ and 9°52′N along the crest of the East Pacific Rise (EPR). Dramatic changes in biological community structure and vent fluid chemistry have been documented throughout this region since the eruptive event. By April 2004, mussels (Bathymodiolus thermophilus) dominated the faunal assemblages at several of the vent sites formed during of after the 1991 eruptions, whereas other habitats within the region were dominated by the vestimentiferan Riftia pachyptila. In the present paper, we build upon the extensive data sets obtained at these sites over the past decade and describe a manipulative experiment (conducted at 9°49.94′N; 104°14.43′W on the EPR) designed to assess interrelationships between vent fluid chemistry, temperature, biological community structure, and seismic activity. To this end, in situ voltammetric systems and thermal probes were used to measure H2S/HS− and temperature over time in a denuded region of an extensive mussel bed in which an exclusion cage was placed to inhibit the subsequent migration of mussels into the denuded area. Fluid samples were taken from the same locations to characterize the associated microbial constituents. Basalt blocks, which were placed in the cage in April 2004 and subsequently recovered in April 2005, were colonized by more than 25 different species of invertebrates, including numerous vestimentiferans and remarkably few mussels. Recorded temporal changes in vent fluid chemistry and temperature regimes, when coupled with microbiological characterization of the vent fluids and seismic activity data obtained from ocean bottom seismometers, shed considerable light on factors controlling biological community structure in these hydrothermal ecosystems.

Hydrothermal Vent Mussel Habitat Chemistry, Pre- and Post-Eruption at 9°50′North on the East Pacific Rise

Abstract Between October 2005 and March 2006, a seafloor volcanic eruption occurred at 9°50′N East Pacific Rise (EPR), establishing a “time zero” for characterizing newly-formed hydrothermal vent habitats and comparing them to pre-eruption habitats. Before the eruption, mussels (Bathymodiolus thermophilus) formed large aggregates between 9°49.6′ and 9°50.3′N. After the eruption, the few mussels remaining were in sparsely-distributed individuals and clumps, seemingly transported via lava flows or from mass wasting of the walls of the axial trough. In situ voltammetry with solid state gold-amalgam microelectrodes was used to characterize the chemistry of vent fluids in mussel habitats from 2004 to 2007, providing data sets for comparison of oxygen, sulfide, and temperature. Posteruption fluids contained higher sulfide-to-temperature ratios (i.e., slopes of linear regressions) (10.86 μM °C−1) compared with pre-eruption values in 2004 and 2005 (2.79 μM °C−1 and −0.063 μM °C−1, respectively). These chemical differences can be attributed to the difference in geographic location in which mussels were living and physical factors arising from posteruptive fluid emissions.

Variation in Sulfur Speciation with Shellfish Presence at a Lau Basin Diffuse Flow Vent Site

Abstract Carbon fixation by sulfur-oxidizing chemosynthetic bacteria forms the base of the food chain in deep-sea (diffuse-flow) hydrothermal vent ecosystems. Temperature and the availability of oxygen and reduced sulfur are believed to be factors that contribute to the structure of hydrothermal vent communities. Sulfur concentration and speciation can change rapidly as highly reducing vent fluids mix with cold oxygenated seawater, thus the path followed by source water before passing over organisms hosting sulfur-oxidizing endosymbionts may have important implications for these animals. Here we show an apparent correlation between the zonation of symbiont-containing species and the sulfur chemical speciation (sulfide, polysulfides, thiosulfate) in the water bathing them. We also report in-situ measurements of thiosulfate (S2O3 2−) in hydrothermal fluids, predominantly in the area inhabited by the mussel, Bathymodiolus brevior. These results provide field evidence of environmental levels of thiosulfate that may be capable of supporting thiosulfate-utilizing symbionts at hydrothermal vents. The three dominant shellfish species were arranged concentrically in a distinct bulls eye pattern at our study site. Alviniconcha sp. 1 snails inhabited the central, most reducing sulfide-rich zone, Ifremeria nautilei snails formed a thin band surrounding the Alviniconcha, and B. brevior mussels were farthest away from the source fluid in the most oxidized region. After removal of many of the Alviniconcha, some I. nautilei moved into the vacated space, whereas the B. brevior remained around the extreme periphery of the area impacted by the diffuse flow. These results suggest that diffuse flow chemistry is one of the key parameters affecting organism distribution.