CRYPTOENDOLITHIC GROWTH OF THE RED ALGA GALDIERIA-SULPHURARIA IN VOLCANIC AREAS

The habitat of the acido- and thermophilic red algae Galdieria sulphur aria and Cyanidium caldarium was examined in acidic hot sulphur spring s in the vicinity of Naples (Italy). These species grew on soil and ro cks, but a large part of the populations was cryptoendolithic. The end olithic algal layer (1-3 mm in thickness) was covered by amorphous sil ica (1-2 mm in thickness) containing traces of hydrotroilite (FeS. nH( 2)O) and elemental sulphur. Organotrophic bacteria and fungi were not found in the algal layer. Light penetration measurements showed that 0 .1-1% of the sunlight reached the upper part of the algal layer. Thus, low-light-adapted algae should be able to perform some photosynthesis in this endolithic habitat. Under conditions where light is even more limited, e.g. in winter or after darkening of the covering layer, man y of the cells might not survive. Aqueous extracts of these algae are excellent growth substrates for Galdieria sulphuraria. Therefore, we p ropose that compounds released from dead cells in the endolithic layer are used by the surrounding Galdieria cells for heterotrophic metabol ism. This would increase their chance of surviving prolonged periods u nder detrimental conditions.