Anoxic thermomineral cave waters and bacterial mats as habitat for freshwater nematodes

A unique chemoautotrophic system of floating microbial mats was examined in a subterranean cave in southern Romania. Oxygen measurements were made with a recently developed technique applying micro-optodes. The oxygen uptake rate of the anoxic and sulfidic cave waters over the atmosphere/water interface was as high as 103.3 plus or minus 9.1 mmol O sub(2) m super(-2) d super(-1). Floating microbial mats consisting primarily of sulfide oxidizers and fungal mycelia were found to be adapted to reduced oxygen supply and thrived even under strict anoxia. These 2 mm thick mats were inhabited by 5 different species of nematodes, reaching densities of 9.8 x 10 super(6) ind. m super(-2). Possible alternative pathways for growth of the mats and also for the persistence and reproduction of nematodes under strict anoxic conditions are discussed.