THE SPECTACULAR MACROSCOPIC MICROBIAL BIOSIGNATURES OF LAVA TUBE CAVES

Lava tube caves in environments as wet as tropical oceanic islands, and as dry as the Mojave Desert sport frequently flamboyant macroscopic microbial/mineral deposits. These often colorful or structurally elaborate indicators are the product of microbial physiology combined with their abilities to transform materials resulting in biomineral deposits, sediment trapping, pigment production, and creation of distinctive patterning. All of these visually detectable phenomena are a reflection of the acquisition of energy and transformation of materials within these systems. The widespread distribution of volcanic cave habitats on Earth provide a globally distributed suite of habitats that vary along important environmental gradients including temperature, humidity, and access to surface-derived organics or the lack thereof and greater reliance of such microbial communities on variations on chemolithotrophy. Enormous biodiversity is present partly controlled by these environmental parameters, but also controlled by nuances of the interaction of bedrock composition and textures, and possibly intrinsic heterogeneity caused by processes internal to the microorganisms themselves. The deposition of minerals that are facilitated by microbial physiological properties and processes result in preservation of the microbial behavior in a tangible mineral form that can be detected and studied even if the particular habitat later becomes unfavorable for organisms to grow. The often subtle fracture-dominated seepage hydrology of many lava tubes provides an additional critical variable that contributes to the complex package of factors controlling the distribution of microbial types and macroscopic indicators. The study of these systems necessarily involves considerations of the hydrology, underlying geology, resulting mineralogy, and biology, thus making a systems approach essential.