Preliminary biological characterization of the Saldanha hydrothermal field at the Mid-Atlantic Ridge (36 degrees 34 ' N, 32 degrees 26 ' W, 2200 m)

A preliminary description of the biology of the Saldanha hydrothermal field in the Mid-Atlantic Ridge (36 degrees 34'N, 32 degrees 26'W, 2200 m) is given, based on direct observation, video images and samples. Venting occurs mainly in a diffuse way through sediment, but hydrothermal fluid discharges are visible through centimeter-long orifices, scattered on the sediment, over an area of approximately 400 m(2), at depths between 2,200 and 2,220 metres. Emitted fluids are transparent, with a temperature of 7-9 degrees C. An almost complete absence of macro- and megafauna around the venting orifices was found. The only vent invertebrate identified was the gastropod Phymorhynchus sp., with only two juvenile specimens caught. A careful examination of the images taken at these orifices showed bacteria-like filaments undulating with fluid discharge. At the level of the benthic bathyal megafauna the dominant species seemed to be the sponge Cinachyra sp. (Demospongiae, Spirophorida, Tetillidae). At least 4 species of fish are new records from the area.