Abstract:
Observations were made on the distribution, morphology, and chemoautotrophic potential of microbial mats found in submarine caves of dolomitized limestone which contain hydrothermal sulphidic springs at Cape Palinuro, Italy. The distribution of microbial mats is closely associated with the flow of hydrothermal fluid from springs whose activity is intermittent and initiated during low tide. Fluid emitted from active springs in the Grotta Azzurra has a maximum temperature of 24.6 degrees C and is enriched in dissolved sulfur species (H2S, S2O32-) and dissolved gases (CH4, CO2). However, it is depleted in NaCl and dissolved O-2, in comparison with ambient seawater. This fluid is less dense and rises above the ambient seawater to form a visible thermocline and chemocline separating both lavers in the submarine caves. Microbial mats were attached to rock surfaces immersed in fluid above the chemocline and were differentiated into brown and white forms. Brown mats were composed of trichomes (4.2 0.1 mu m and 20.3 0.7 mu m in diameter) resembling the calcareous rock-boring cyanobacterium Schizothrix and clusters (6 mu m in diameter) of sarcina-like cells morphologically resembling methanogenic bacteria. White mats were composed of attached filaments resembling Beggiatoa (19.3 0.5 mu m, 39.0 1.7 mu m, and 66.9 3.3 mu m in diameter) and Thiothrix (4.2 0.2 mu m in diameter). Flexibacteria (