Search

Aim Deep-sea hydrothermal vents are unstable habitats that are both spatially and temporally fragmented. In vent species, a 'short-term insurance' hypothesis would lead us to expect mostly self-recruitment, limiting the loss of larvae in the deep ocean or water column and increasing genetic differentiation over the time elapsed since colonization. Alternatively, a 'long-term insurance' hypothesis would support the prediction of selection for large-scale dispersal, to ensure long-term persistence in these ephemeral habitats. The main goal of this study was to infer the spatial and temporal distribution of genetic diversity of the shrimp Rimicaris exoculata, which forms high-density local populations on hydrothermal vents along the Mid-Atlantic ridge. Location Deep-sea hydrothermal vents along the Mid-Atlantic Ridge. Methods We used sequences of mitochondrial cytochrome c oxidase subunit I (COI, 710 bp) to assess the spatio-temporal distribution of genetic diversity across five hydrothermal fields from 36 degrees N to 4 degrees S. Results In contrast to previous results from pioneer studies, very high haplotype diversity was observed in vents across the entire region (i.e. 0.69-0.82), indicating current large effective population size and low drift. The star-like shape of the network of haplotypes, the lack of spatial genetic structure and the significance of tests reflecting demographic effects, together with the fitting of a population expansion model, all support a recent population expansion. Main conclusions Our results suggest a very recent common history of R. exoculata populations/demes along the Mid-Atlantic Ridge, derived after a common bottleneck or founder event and followed by a concomitant demographic expansion. This study therefore suggests a large effective population size and/or high dispersal capacity, as well as a possible recent (re) colonization of Mid-Atlantic hydrothermal vents by R. exoculata.

Aim Deep-sea hydrothermal vents have now been reported along all active mid-ocean ridges and back-arc basins, but the boundaries of biogeographic entities remain questionable owing to methodological issues. Here we examine biogeographic patterns of the vent fauna along the East Pacific Rise (EPR) and determine the relative roles of regional and local factors on the distribution of biodiversity associated with mussel beds along a poorly explored zone, the southern EPR (SEPR). Location East Pacific Rise. Methods A species list of macrobenthic invertebrates along the EPR was compiled from the literature and supplemented with data recovered during the French research cruise BIOSPEEDO carried out in 2004 along the SEPR. Biogeographic patterns were assessed by combining the identification of morphological species with a molecular barcoding approach. A multivariate regression tree (MRT) analysis was performed to identify any geographic breaks, and an empirical distribution of species richness was compared with predictions provided by a mid-domain effect model. Macrofaunal community structure associated with mussel beds along the SEPR was analysed in relation to environmental factors using cluster and canonical redundancy analyses. Results Sequencing of the cytochrome c oxidase subunit I gene revealed the occurrence of several cryptic species complexes along the EPR, with the equator separating the southern and northern clades. Furthermore, during the BIOSPEEDO cruise at least 10 still unnamed species were collected between 7 degrees 25' S and 21 degrees 33' S. The shift in community structure identified by MRT analysis was located south of 17 degrees 34' S or south of 13 degrees 59' S, depending on the data used, suggesting that the southern part of the SEPR (17 degrees 25'-21 degrees 33' S) constitutes a biogeographic transition zone in the vent fauna along the EPR. At a regional scale, latitude combined with the type of venting was significantly correlated with the commu

The Eiffel Tower edifice is situated in the Lucky Strike hydrothermal vent field at a mean depth of 1690 m on the Mid-Atlantic Ridge (MAR). At this 11-m-high hydrothermal structure, different faunal assemblages, varying in visibly dominant species (mussels and shrimp), in mussel size and in density of mussel coverage, were sampled biologically and chemically. Temperature and sulphide (Sigma S) were measured on the different types of mussel-based assemblages and on a shrimp-dominated assemblage. Temperature was used as a proxy for calculating total concentrations of CH4. Based on the physico-chemical measurements, two microhabitats were identified, corresponding to (i) a more variable habitat featuring the greatest fluctuations in environmental variables and (ii) a second, more stable, habitat. The highest temperature variability and the highest maximum recorded temperatures were found in the assemblages visibly inhabited by alvinocaridid shrimp and dense mussel beds of large Bathymodiolus azoricus, whereas the less variable habitats were inhabited by smaller-sized mussels with increasing bare surface in between. Larger mussels appeared to consume more Sigma S compared with smaller-sized (< 1 cm) individuals and thus had a greater influence on the local chemistry. In addition, the mussel size was shown to be significantly positively correlated to temperature and negatively to the richness of the associated macrofauna. The presence of microbial mats was not linked to specific environmental conditions, but had a negative effect on the presence and abundance of macro-fauna, notably gastropods. Whereas some taxa or species are found in only one of the two microhabitats, others, such as polychaetes and Mirocaris shrimp, cross the different microhabitats. Temperature was proposed to be a more limiting factor in species distribution than Sigma S.