Microbial distribution on sandstone with honeycomb weathering along rocky coasts in a subtropical environment

Abstract Weathering processes occur on terrestrial surfaces in combination with atmospheric and oceanic environments. Salt weathering often results in the formation of a honeycomb structure (tafoni) and a concave microrelief. Tafoni has been investigated extensively in geomorphological studies, whereas causative factors, including microbial effects, have rarely been investigated in previous studies. This study discusses the distribution of microbial communities as an environmental factor in honeycomb weathering on sandstone surfaces. The study sites are located on Yonaguni Island in the Ryukyu Arc, where Miocene sandstone (Yaeyama Group) is extensively exposed on the island and forms numerous cliffs with a honeycomb structure resulting from physical disintegration due to salt weathering. Microbial community analysis identified potential candidates that could contribute to honeycomb weathering. Acidobacteria can dissolve iron-rich minerals through the production of organic acids, whereas other bacteria, such as Actinobacteria, utilize iron ions via siderophores. Microbial activity, particularly associated with abundant Cyanobacteria, may contribute to chemical and physical weathering by increasing decomposition and disintegration.