No abstract

Until1985, seven vent fields were described from the Mid-Atlantic Ridge (MAR). An eighth field, Mount Saldanha (36° N), discovered in 1998, showed unusual geological and biologica! settings. Vent sites on the MAR exhibit varied environmental conditions, resulting from depth variation of the axis and associated physical parameters, and different source rocks. These could be considered as first order (i.e. most dominant) factors affecting the composition of vent communities on the MAR, in contrast to the East Pacific Rise (EPR) where geographical isolation appears to be a major determinant of fauna! differences. In this paper, the geological setting and vent fluid composition of the fields are considered together with their community composition to tentatively ascertain the order of a hierarchy between dispersa! and environmental control. The deepest fields (>3000 m) are rather stable systems. The shallower fields, especially Rainbow and Menez Gwen, present some evidence of instability in time and space. The variability in fluid composition is related to phase separation processes (boiling/distillation of subsurface vent fluids) and to the nature of the basement rocks. Depending on depth, phase separation produces gas-enriched and metal-depleted fluids (Menez Gwen, Lucky Strike) or metal-enriched brines (Rainbow, TAG). In addition, high methane content characterises the fluids formed in ultramafic rocks (Rainbow, Logatchev) compared to basaltic rocks. The discrepancy in mineral particulate fluxes at Lucky Strike and Menez Gwen, on one hand, and TAG and Rainbow, on the other, is correlated to the predominance of the vapour or brîne phase. The semi-quantitative description of the fauna! composition of the different vent fields displays a continuum from Rimicaris-dominated to Bathymodiolus-dominated assemblages. Rather than geographic or bathymetric zonation, this gradati an appears tobe related to the metal content of the fluids. In addition, the penetrati an of non vent species into the vent environment increases with decreasing hydrostatic pressure and/or metal content in the fluids. Similarity analysis between vent communities shows that similarity is strongest between Menez Gwen and Lucky Strike (the shallowest fields), less significant between these sites and Rainbow, and weakest for Snake Pit. The inverse relationship between filter feeding organisms and metal concentration in vent fluids could result from a hindrance of mussel bed development by particulate or toxic metal fluxes, and has to be further investigated. Conversely, high metal and particulate content would less affect the more mobile Rimicaris populations. Considering specific similarities of endemic fauna between the faur best known hydrothermal vents, the distance between vent fields appears tobe a first order parameter. Nevertheless, within the proximity of the Azores Triple Junction area, and in the absence of geographical discontinuity, the similarity between fields stays rather low suggesting fauna! islands that have distinct composition and h...

International audienceBiological invasions are a major threat to the world's biodiversity with consequences on ecosystem structure and functioning, species evolution, and human well-being (through ecosystem services). Conservation of biological diversity and management of biological resources require multi-level management strategies on non-native species, in order to (1) prevent biological introductions, (2) detect non-native species at an early stage of the introduction, and (3) eradicate or maintain at a low level of population density non-native species that were successfully introduced. A pre-requisite to any control measures on non-native species is the ability to rapidly and accurately identify the putative threatening alien species. DNA barcoding, and its recent extension, DNA metabarcoding are complementary tools that have proved their value in the identification of living beings. Here we review their use in the identification of non-native species at several steps of the introduction processes, and how they can be applied in the control and management of biological introductions. Through examples covering various taxa and ecosystems (terrestrial, freshwater, marine), we highlight the strengths and weaknesses of approaches that we foresee as crucial in the implementation of early warning strategies

The polychaete family Polynoidae (scale-worms) is well-represented at deep sea hydrothermal vents. Most species are free-living in a wide range of habitats: from high-temperature hydrothermal `chimney' walls to diffuse venting areas. Conversely, species of the genus Branchipolynoe live inside the mantle cavity of vent and seep mytilids. Specimens, morphologically close to Branchipolynoe seepensis, have been reported from all the known vent areas on the Mid-Atlantic Ridge (MAR), with varying infestation rates (0–6 individuals per host). Reproductive tract, gametogenesis and population structures were examined for specimens from the Lucky Strike vent field (MAR) in order to test whether this species displays dwarf males, protandric hermaphroditism or differential mortality between males and females. Observations of histological sections reveal the presence of fully developed ovaries in females which originate ventrally in segments 7–9 and of an unusual genital tract in which both sperm and mature oocytes are stored. Oogenesis is intraovarian and quasi-continuous. The vitellogenic oocytes are only free in the coelom at their terminal growing stage and are then transferred into an ovisac through spermathecae. The species displays an external sexual dimorphism in the number of genital papillae and the shape of the pygidial appendages. Sex ratios showed significant deviations from a 1:1 expected ratio, in favour of females. The modal decompositions of size–frequency histograms show the occurrence of three modes in females and only two modes in males, indicating discrete breeding periods. The two first modes were not significantly different between males and females. These results indicate that B. seepensis forms heterosexual pairs and uses internal fertilization to reproduce during discrete spawning periods. Differential mortality between males and females is likely to shape size-histograms as observed by preventing males from reaching the female proportions. Such an observation could be a result of either cannibalism on larger males, small sizes facilitating the male escape, or natural predation when males move from one bivalve to another to breed.