MASS DEVELOPMENT OF NOSTOC-MICROSCOPICUM (CARMICHAEL) HARVEY EX BORNET AND FLAHAULT IN A CAVE IN CLARENS-SANDSTONE OF THE DRAKENSBERG MOUNTAINS, SOUTH-AFRICA (GOLDEN-GATE-HIGHLANDS-NATIONAL-PARK)

We report about an unusual mass development of the cyanobacterium Nost oc microscopicum in a 25 m deep cave in Clarens-sandstone (Karoo-syste m, Stormberg formation) of the Drakensberg mountains, South Africa. Be sides N. microscopicum, several other genera of cyanobacteria (Chrooco ccus, Gloeocapsa, Nostoc, Oscillatoria) occurred, but were less abunda nt. Numerous diatoms of the genera Cymbella, Denticula and Nitzschia w ere also present within a gelatinous matrix on the surface of the rock . Seepage water, coming from the wall and the ceiling at the back of t he cave is the only source of water. The pH of the water, as well as p H of the rock, showed strongly alkaline values (9-9.2). The growth env ironment of N. microscopicum and the diatoms is, to some extent, compa rable to that found in soda-lakes or the so called ''Sodium-Solontscha k'', a salt containing, alkaline soil type. N. microscopicum was isola ted and kept in culture for taxonomical studies, which will be discuss ed in this paper.