Abstract
Hydrothermal vent sulfide edifices contain some of the most extreme thermal and chemical conditions in which animals are able to live. As a result, sulfide edifices in the East Pacific Rise, Juan de Fuca Ridge, and Mid Atlantic Ridge vent systems often contain distinct faunal assemblages. In this study, we used high-resolution imagery and in-situ physico-chemical measurements within the context of a Geographic Information System (GIS) to examine community structure and niche differentiation of dominant fauna on sulfide edifices in the Eastern Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) in the Western Pacific Ocean. Our results show that ELSC and VFR sulfide edifices host two distinct types of communities. One type, that covers the majority of sulfide edifice faces, is overall very similar to nearby lava communities and biomass is dominated by the same chemoautotrophic symbiont-containing molluscs that dominate lava communities, namely the provannid gastropods Alviniconcha spp. and Ifremeria nautilei and the mytilid bivalve Bathymodiolus brevior. The spatial distribution of the dominant molluscs is often a variation of the pattern of concentric rings observed on lavas, with Alviniconcha spp. at the tops of edifices where exposure to vent flow is the highest, and I. nautilei and B. brevior below. Our physico-chemical measurements indicate that because of rapid dispersion of vent fluid, habitable area for symbiont-containing fauna is quite limited on sulfide edifices, and the realized niches of the mollusc groups are narrower on sulfide edifices than on lavas. We suggest that competition plays an important role in determining the realized distributions of the mollusc groups on edifices. The other habitat, present in small patches of presumably hot, new anhydrite, is avoided by the dominant symbiont-containing molluscs and inhabited by crabs, shrimp and polynoids that are likely more heat tolerant. The ratio of sulfide concentration to temperature anomaly of vent fluids was significantly different between sulfide edifice sites and lava sites in the southern vent fields but not in the northern vent fields. We suggest that this is due to increased sulfide consumption by a large microbial consortium associated with the more friable andesitic lava substrates in the south.
Highlights
Boulevard-230 Lawrence Hall, 5234 University of Oregon, Eugene, OR 97403-5234, USA.Present address: Grice Marine Laboratory, College of Charleston, 205 Fort Johnson Road, Charleston, SC 29412, USA.Present address: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA.Present address: University of North Carolina Wilmington, Wilmington, NC 28403, USA.Basin, the Eastern Lau Spreading Center (ELSC, from $ 191S to $ 211S) and the Valu Fa Ridge (VFR, from $ 211S to 231S), are located between a remnant arc (Lau Ridge) and an active volcanic arc (Tofua Volcanic Arc), west of the Tonga-Kermadec Trench (Fig. 1)
Mottl et al (2011) found that sulfide concentrations in endmember fluid decrease from north to south along the ELSC/VFR with the highest concentrations in endmember fluid at Tu’i Malila being three times lower than concentrations measured in Kilo Moana
The decrease in sulfide concentrations in endmember fluid from north to south along the ELSC to the VFR is consistent with the higher sulfide to temperature ratios observed in the north (Gartman et al, 2011; Luther et al, 2012)
Summary
The Eastern Lau Spreading Center (ELSC, from $ 191S to $ 211S) and the Valu Fa Ridge (VFR, from $ 211S to 231S), are located between a remnant arc (Lau Ridge) and an active volcanic arc (Tofua Volcanic Arc), west of the Tonga-Kermadec Trench (Fig. 1) These regions have been the focus of integrated biological and geological studies because crustal chemistry, spreading rates, lithospheric thickness and mantle properties all vary from north to south along the spreading center (Baker et al, 2006; Ferrini et al, 2008; Martinez et al, 2006; Pearce et al, 1994; Taylor et al, 1996, Tivey et al, 2012). The crustal morphology changes quite dramatically, with the northern sites being characterized by deep, flat axial basins and containing more faulting and fissuring than the southern sites, which are characterized by shallow, peaked ridges (Ferrini et al, 2008; Martinez et al, 2006)
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