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 wit h a recently developed technique applying micro-optodes. The oxygen uptake rate of the anoxic and sulfidic cave waters over the atmosphere/water inter face was as high as 103.3 +/- 9.1 mmol O-2 m(-2) d(-1). Floating microbial mats consisting primarily of sulfide oxidizers and fungal mycelia were foun d to be adapted to reduced oxygen supply and thrived even under strict anox ia. These 2 mm thick mats were inhabited by 5 different species of nematode s, reaching densities of 9.8 x 10(6) ind, m(-2). Possible alternative pathw ays for growth of the mats and also for the persistence and reproduction of nematodes under strict anoxic conditions are discussed.