**4. Conclusions**

This high diversity may partly be caused by the lack of photosynthetically active radiation which is almost the only stressor in caves, whereas subaerophytic habitats are significantly affected by many stress factors such as excessive irradiance, UV, desiccation, rapid tempera-

It is well known that cyanobacteria are considered the pioneering inhabitants in the caves colonization. Cyanobacteria prevail in the cave entrances compared to the other microalgae [39]; however, they colonize the various parts of the cave entrances, where biodiversity of organisms is the lowest [22]. Among many factors influencing cavernicolous species, water relations in caves are important for cyanobacteria to growth and their colonization [44]. Lamprinou et al. [4] stated that cavernicolous species are dominated by cyanobacteria, which represent the first photosynthetic colonizers on the calcareous surfaces usually thriving both as epiliths and as endoliths. Epilithic communities form extensive dark-green coverings created by *Phormidium breve* as dominant species, or pale blue-green to whitish coverings consisting *Tolypothrix epilithica*. Lamprinou et al. [30] observed predominance of Oscillatoriales group over Chroococcales, in the dim light zone, and also in the entrance, especially in speleothems exposed to light, but their presence is attributed to the chasmoen-

Round [45] differentiated the distribution of microorganisms depending on the access of either natural or artificial light. Growing of cyanobacteria visible in the form of different color patches on cave walls is undoubtedly connected with the availability of light and specific limestone cave microclimate. This microclimate in caves is influenced by air circulation, hydrological conditions, and isolation of cave from the outside thermal influences [21]. Microscopic observations [21] revealed that cyanobacteria are arranged in particular communities named patinas, which are blue, brown, green, or gray. These communities contain coccoid forms that are frequently accompanied by filamentous forms that are irregularly distributed and do not present stratification. Generally, there are two different areas of the caves. One area is the entrance, where the microclimate is influenced by the light, temperature, and relative humidity fluctuating throughout the year. Patina is greenish-bluish formed by coccoid species only, and there are also grayish patina constituted by coccoid and filamentous species. The second area is the inside with a stable temperature and relative humidity and very low light. The patina found there are greenish-bluish formed by only coccoid species, brownish-gray patina constituted by coccoid forms and filamentous forms, and bluish-grayish patina formed by coccoid forms and filamentous forms. On the other hand, the cave tourism is an important factor causing increase of temperature and environmental changes. Pouličková and Hašler [11] observed the majority caves in Europe are characterized by an average humidity (circ. 70%), and their entrance walls usually are covered by cyanobacteria. The development of cave tourism requires alteration of natural corridors, installation of lighting, pathways, platforms, and associated infrastructure [46]. On the other hand, caves impacted by severe disturbances, including tourism and artificial illumination, have never been completely restored to their former ecological state [47]. Under such conditions, the oligotrophic nature of cave environments is expected to change through organic inputs that alter both the food web and the abundance and distribution of

ture change, and their combinations.

52 Cyanobacteria

dolithic mode of life.

cave organisms [40].

An investigation of the diversity and ecology of cyanobacteria in limestone caves has been conducted for many years. Cyanobacteria were the dominant group of phototrophs colonizing cave walls. Chroococcales was the most common cyanobacterial order (with *Gloeocapsa* as the most frequently encountered cyanobacterial genus), followed by Nostocales. The most widespread and abundant species were *Aphanocapsa muscicola, Gloeocapsa biformis,* and *Nostoc commune.* Caves impacted by severe disturbances, including tourism and artificial illumination, were never been completely restored to their former ecological state [47]. Principally, every visitor entering a cave, from the professional speleologist to tourists, has the potential to exert a negative impact on the cave ecosystem.
