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...

This paper presents an analysis of the distributional patterns of blenniids (Pisces: Blenniidae) in the north-eastern Atlantic. Two peaks of species diversity were found, both in terms of number of species and number of endemics: one in the tropical African coast and another in the Mediterranean Sea. A cluster analysis of similarity values (Jaccard coefficient) among the eastern Atlantic zoogeographical areas, revealed the following groups: a north temperate group, a tropical group formed by the tropical African coast and Mauritania, another group formed by the islands of Cape Verde, a south temperate group (South Africa), and a southern Atlantic group formed by the islands of Ascension and St Helena. Within the north temperate group, the subgroups with higher similarities were: Azores and Madeira, Canary Islands and Morocco, and the Mediterranean and the Atlantic coast of the Iberian Peninsula. Based on affinity indices, the probable directions of faunal flows were inferred. The tropical coast of Africa and the Mediterranean emerged from this analysis as probable speciation centres of the north-eastern Atlantic blenniid fauna. The Mediterranean may have also acted as a refuge during glacial periods.

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Fish assemblages in Cais do Carva˜o Bay, Madeira Island, a proposed marine protected area (MPA), were determined from a diver visual census. A total of 32 transect counts were performed. Habitats sampled included sandy bottom, rocky boulders, vertical walls and rocky outcrops. Species richness, diversity, density, trophic structure, size and spatial organization were documented for the fish assemblages. Forty-four species from 23 families were encountered; 32% belonged to Sparidae (10) and Labridae (four). The greatest species richness (25) was observed in rocky boulder habitat at 10-15 m depth, while the lowest (five) occurred over a deeper sand habitat. The greatest density (760Á5 individuals per 100 m 2 ) was recorded over rocky outcropping (20-25 m deep), and the lowest of 11Á6 individuals per 100 m 2 was over a sand bottom at 10-15 m depth. Thalassoma pavo, Abudefduf luridus and Chromis limbata had higher densities on hard bottoms, while Heteroconger longissimus was the most abundant species in sand bottom habitats. No significant differences were detected for all indices calculated among depth intervals for sand and rocky boulder stations. Sand and rock boulder substratum, however, differed significantly for the 10-15 m depth stratum. # 2005 The Fisheries Society of the British Isles

The diets of 33 fish species from the southern Portuguese slope, at depths between 498 and 740 m were studied through the examination of stomach contents. Species of scyliorhinids, squalids, rajids. chimaerids, anguilliforms, notacanthids, macrourids, gadids and merluccids, with pelagic, benthopelagic and benthic modes of life were examined. Nezurnia sclerorhynchus feeding habits were studied in detail. Its diet its dominated by amphipods. No differences of prey preferences were recorded corresponding to predator size classes. The studied predators can exploit a wide range of prey, but they feed mainly on benthopelagic and epibenthic material. Consequently it is difficult to establish distinct feeding guilds, so confirming a generalist type of feeding for most of the upper slope dwelling fishes.