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Associated with the Lost City Hydrothermal Field Kate L. Buckman and Timothy M. Shank Woods Hole Oceanographic Institution, Biology Dept. Woods Hole, MA 02543
In 2001, an off-axis peridotite-hosted hydrothermal system supporting up to 60 meter tall carbonate-brucite chimneys was discovered on the Atlantis Massif (30°07.4'N, 42°07.24'W; 700-800m depth). In 2003, a second interdisciplinary expedition returned to this site, the Lost City Hydrothermal Vent Field (LCHF), to understand the linkages among hydrothermal alteration of the mantle, geochemistry, and biological ecosystems within this environment. The Lost City vent field features many components that offer opportunities to identify novel ecological niches and new species (with new adaptations) associated with potentially unique (yet prevalent) chemical habitats. These components include Lost City's close proximity (<15 kilometers) to, yet pronounced depth difference (~3000m) from the Mid-Atlantic Ridge floor, and unique fluid chemistry derived from serpentinization reactions and production of carbonate chimneys at the seafloor. Lost City also offers the opportunity to identify the evolutionary relationships of chemosynthetic fauna in comparison to those endemic to vents and seeps. Preliminary characterization of actively venting carbonate habitats (~10-40?C) indicated they were dominated by several species of gastropods and amphipods, including Bouvierella curtirama and Primno evansi. Also present were polychaetes, nematodes, euphausids, foraminifera, ostracods, bivalves (including mussels), stomatopods, and demosponges. Non-venting habitats (e.g., the sides of inactive chimneys, sedimented areas, and breccia cap rock) were occupied by Lophelia, Desmophyllum and gorgonian corals, galatheid crabs, mussel shells, gastropods, foraminifera, pteropods, urchins, asteroids, limpets, and ophiuroids. The dominant mobile fauna near actively venting edifices was a purple-gray ~10 to 30cm-long cut-throat eel (Synaphobranchus kaupi). Wreckfish (Polyprion americanus) were also abundant throughout the field as well as number of other unidentified fish. Preliminary observations indicate that the upper pelagic and mid-Atlantic deep-sea fauna (>200m) have a marked presence on Lost City faunal composition (e.g., the presence of pteropods, forams, and amphipods), though some vent fauna are also present. A cursory comparison of biomass between the dominant faunas of Lost City, Mid-Atlantic Ridge, East Pacific Rise, and Juan de Fuca, suggests that Lost City supports significantly lower biomass, with the large majority of the dominant fauna on the order of hundreds of microns or less in length. Results from ongoing phylogenetic studies of Lost City species will be presented to shed light on the role of depth, fluid chemistry, and the presence of non-endemic species in controlling community composition. These findings will be used to examine the role of Lost City-type vent fields (a potentially ubiquitous style of venting along the Mid-Atlantic Ridge) as stepping stones or evolutionary refugia for the chemosynthetic fauna along the Mid-Atlantic Ridge.
Within Rimicaris exoculata Along the Northern Mid-Atlantic Ridge Diane K. Peohls and Timothy M. Shank Woods Hole Oceanographic Institution, Biology Department Woods Hole, MA 02543 Abstract Genetic communication between disjunct communities of hydrothermal vent shrimp, Rimicaris exoculata, on the Mid-Atlantic Ridge (MAR) was investigated using sequence data from the mitochondrial cytochrome b (cyt b). Adults and juvenile Rimicaris exoculata were collected from four deep MAR vent fields, Rainbow, Broken Spur, TAG and Snake Pit in 2002 and from TAG in 2003 to include a study of temporal genetic variation. Previous allozyme studies suggest genetic homogeneity among TAG, Snake Pit, and Broken Spur; however, prior results have demonstrated that allozymes may not recover existing genetic subdivision. High-relief transform faults, dynamic latitudinal ocean circulation patterns (perhaps associated with transform faults or fracture zones), and/or the relative stability of venting activity along the slow-spreading Mid-Atlantic Ridge present potential mechanisms for genetic isolation between vent fields hundreds of kilometers apart. Complete panmixia was not observed given haplotype differences between Rainbow and TAG, Broken Spur and Snake Pit, nor between adults and juveniles. However, phylogeographic, coalesence, and AMOVA analysis of the cyt b gene at these four vent fields along the MAR are consistent with allozyme data, suggesting that high levels of gene flow do occur within R. exoculata. Larvae likely overcome the barriers to dispersal by transport in upper ocean currents beyond the direct influence of the ridge topography. Despite observed geographic homogeneity, temporal variation between years and between adults and juveniles may offer insight into dispersal patterns on an ecological scale. Barriers to dispersal may still exist, driven instead by upper ocean current regimes such as the separation between the North Atlantic Central Gyre and its southern counterpart. In order to accurately address the connectivity within R. exoculata, other ocean basins must be examined. |