Diatom flora in subterranean ecosystems: a review

Abstract

Subterranean ecosystems are often severely oligotrophic settings with low supplies of degradable organic matter from the surface due to a lack of light and primary producers. Intense tourism and recreational caving are the greatest human direct influences on cave ecosystems, which significantly modify the entire subterranean ecology. Exocellular polymeric substances (EPSs), which are made of polysaccharides, proteins, lipids, and nucleic acids, are produced by autotrophic organisms (the so-called lampenflora), which are mostly composed of cyanobacteria, diatoms, chlorophytes, mosses, and ferns. The adsorption of cations and dissolved organic molecules from the cave formations is facilitated by the anionic EPSs matrix, which also participates in chemical interactions with the substratum (speleothems). This effect may cause the mineral surfaces to corrode when combined with the metabolic activities of the heterotrophic bacteria colonizing such layer (biofilm). In this paper, we explore how artificial lighting affects speleothems by causing biofilms to grow, particularly diatom-dominated ones. When artificial or natural light enters the subterranean habitat, a significant number of diatom species may in fact colonize it. The ideal substrates are typically cave openings, artificially lit walls, and speleothems inside the cave. This review summarizes the data found in all the scientific studies published from 1900 to the present and focuses on the diatom flora colonizing subterranean settings.