Community structure and temperature dynamics within a mussel assemblage on the Southern East Pacific Rise

The composition, biomass and diversity of the fauna in a Bathymodiolus thermophilus mussel assemblage colonizing diffuse flow areas on the SEPR is described and compared with biological characteristics of other hydrothermal assemblages. The spatio-temporal dynamics of temperatures over fine scales within the mussel habitat are characterized using newly-developed statistical approaches. Temperature data obtained from two adjacent habitats (a cirriped assemblage and a bare substratum) are compared. The results of the temperature data show that the mean temperature and the temperature variations were significantly higher in the mussel assemblage (mean temperature: 4.12 +/- 1.85 degrees C) in comparison with 2.40 +/- 0.14 degrees C in the cirriped assemblage and 2.20 +/- 0.23 degrees C on the bare substratum. Discrete temperature measurements showed that temperature data varied both at a broad and fine scales in the mussel assemblage. Finally, analysis of the temperature periodic variability in the mussel assemblage during a 4-day period showed significant periodic modulations near T = 24h. Although not significant, a second trend is also observed around T = 12h. This work represents a step forward to the understanding of species distribution patterns at vents

Microdistribution of Faunal Assemblages at Deep-Sea Hydrothermal Vents in the Southern Ocean

Chemosynthetic primary production by microbes supports abundant faunal assemblages at deep-sea hydrothermal vents, with zonation of invertebrate species typically occurring along physico-chemical gradients. Recently discovered vent fields on the East Scotia Ridge (ESR) in the Southern Ocean represent a new province of vent biogeography, but the spatial dynamics of their distinct fauna have yet to be elucidated. This study determines patterns of faunal zonation, species associations, and relationships between faunal microdistribution and hydrothermal activity in a vent field at a depth of 2,400 m on the ESR. Remotely operated vehicle (ROV) dives obtained high-definition imagery of three chimney structures with varying levels of hydrothermal activity, and a mosaic image of >250 m2 of seafloor co-registered with temperature measurements. Analysis of faunal microdistribution within the mosaiced seafloor reveals a consistent pattern of faunal zonation with increasing distance from vent sources and peak temperatures. Assemblages closest to vent sources are visibly dominated by a new species of anomuran crab, Kiwa n. sp. (abundance >700 individuals m?2), followed by a peltospiroid gastropod (>1,500 individuals m?2), eolepadid barnacle (>1,500 individuals m?2), and carnivorous actinostolid anemone (>30 individuals m?2). Peripheral fauna are not dominated by a single taxon, but include predatory and scavenger taxa such as stichasterid seastars, pycnogonids and octopus. Variation in faunal microdistribution on chimneys with differing levels of activity suggests a possible successional sequence for vent fauna in this new biogeographic province. An increase in ?34S values of primary consumers with distance from vent sources, and variation in their ?13C values also indicate possible zonation of nutritional modes of the vent fauna. By using ROV videography to obtain a high-resolution representation of a vent environment over a greater extent than previous studies, these results provide a baseline for determining temporal change and investigations of processes structuring faunal assemblages at Southern Ocean vents