A review of the distribution of hydrothermal vent communities along the northern Mid-Atlantic Ridge: dispersal vs. environmental controls

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...

Influence of CH<sub>4</sub> and H<sub>2</sub>S availability on symbiont distribution, carbon assimilation and transfer in the dual symbiotic vent mussel <i>Bathymodiolus azoricus</i>

“…In such conditions, stored glycogen (which can reach 10% of the dry mass in B. thermophilus, Smith, 1985) becomes the major energy source for the mussel, and the Embden-Merehof-Parnas glycogenolysis pathway deviates from its normal aerobic route, to carboxylate phosphoenolpyruvate (PEP), producing oxaloacetate (Grieshaber et al, 1994). PEP carboxykinase could thus incorporate 13 C-enriched inorganic carbon entrapped in the valve cavity into oxaloacteate and subsequent end-products such as succinate (as seen in Mytilus edulis, de Zwaan et al, 1983) or other organic acids. However, the effect of any enhanced glycogenolysis would probably result in all tissues displaying the same level of label incorporation, whereas we observe 13 C incorporation mainly in gill tissue, and only to a lesser extent in other tissues.…”

Variation in community structure within hydrothermal vent mussel beds of the East Pacific Rise

“…The most common means of assessing these scales of variability has been by comparison of species' lists among sites on different ridge segments or ridge systems (e.g. Tunnicliffe 1988, Hashimoto et al 1995, Tunnicliffe & Fowler 1996, Tunnicliffe et al 1998, Desbruyères et al 2000, Kojima 2002. In general, species lists do not discriminate faunas of adjacent ridge segments very well; there are overlapping occurrences of the majority of species within vents across approximately 5°of latitude along the northeast Pacific Ridges (Juan de Fuca, Explorer, Gorda Ridges) and across similar distances along the EPR (Tunnicliffe 1988, Tunnicliffe et al 1998.…”

“…not including 'penetrating', non-vent species); for Lucky Strike and Menez Gwen vents (separated by ~50 km), C = 47 (Desbruyères et al 2000). The greater degree of endemicity among vent faunas of MAR vents is thought to be due at least in part to the greater range in depths among MAR vent sites (MAR: 850 to 3500 m; EPR: 2500 to 2600 m), which influences both the chemical character of the venting fluids and the physiological attributes of the organisms (Van Dover et al 1996, Desbruyères et al 2000.Fish and invertebrate faunas of adjacent seamounts (median C = 79; Richer de Forges et al 2001) are more dissimilar than invertebrates faunas of adjacent vent mussel beds (C = 30); seamounts separated by only 1000 km had no shared species (C = 100; Richer de Forges et al 2001), while vents separated by 3000 km shared 38 species (C = 31). Vents are often described as being made up of endemic species (e.g.…”

An overview of chemosynthetic symbioses in bivalves from the North Atlantic and Mediterranean Sea

“…1). Many cold seep sites have been explored at varying depths in the Gulf of Mexico (see Cordes et al, 2010, for review), and several hydrothermal vents sites have been explored on the Mid-Atlantic Ridge (MAR) (Desbruyères et al, 2000;van der Heijden et al, 2012). Other areas have been less intensively investigated, such as deep hydrothermal vents in the Caribbean Sea (Piccard vent field, Mid-Cayman Ridge).…”

“…Exceptions include Bathymodiolus boomerang, which lives partly buried in the sediment at the Barbados seeps (Cosel and Olu, 1998;Duperron, 2010). These mussels occur mostly in areas of diffuse fluid flow, and avoid the hottest or most anoxic niches , Desbruyères et al, 2000. The genera themselves (e.g., Bathymodiolus, Idas, or Adipicola) remain poorly defined based on morphological characteristics, and are clearly non-monophyletic (Carney et al, 2006;Jones et al, 2006;.…”