Epilythic cyanobacteria and algae in two geologically distinct caves in South Africa

Abstract

There is a lack of knowledge on cyanobacteria and algae living in caves in the southern hemisphere. As a result, a pioneer study was undertaken to investigate cyanobacterial and algal community composition in two morphologically and geologically distinct caves in South Africa. Skilpad Cave is characterized by a large sinkhole entrance in a dolomitic landscape. Three zones (light zone, twilight zone and dark zone) were identified based on differences in light intensity. Bushmen Cave, on the other hand, is a rockshelter overhang situated in a sandstone-dominated area and only presents a light and twilight zone. Cyanobacteria and algae were sampled twice, during the summer and winter of 2018 while abiotic factors of interest, i.e. light intensity, temperature and relative humidity, were also measured. A huge diversity of cyanobacteria (14 genera) and algae (48 genera) were identified in the two caves. While some genera were only present in one of the caves, other cosmopolitan genera were found in both caves. The most common genera encountered were Phormidium, Oscillatoria and Nostoc (cyanobacteria), Pinnularia and Luticola (diatoms), Chlorella and Chlorococcum (green algae). Cyanobacteria, green algae and diatoms were also the richest groups (taxa) in terms of the number of genera. More genera were present in the warm, wet season compared to the dry, cold season. Genus richness was positively correlated with light intensity in Skilpad Cave, but negatively in Bushmen Cave. Petalonema alatum, a cyanobacterium encountered in Bushmen Cave, represented a new record for Africa, and therefore, further research on cyanobacteria and algal assemblages in caves in the southern hemisphere is strongly recommended