The first colonists
In the sunless and sterile environment of a newly formed lava tube, life takes hold with surprising speed. The first arrivals are microbes, which form communities on the bare basalt. These pioneer organisms create biofilms—mats of bacteria and archaea that can be white, yellow, or pink. Research in Hawaiian lava tubes has identified a high diversity of these microbes, with many being entirely new to science. One study found that important groups, like bacteria from the phylum Chloroflexi, act as "hub" species, forming the foundation of the tube's earliest ecosystem. These microbes are extremophiles, capable of surviving in harsh conditions with few nutrients. They perform chemosynthesis, deriving energy directly from the minerals in the volcanic rock, essentially "eating" the rock to survive. This process breaks down the basalt and begins the slow formation of soil, paving the way for more complex life.
The age of the lava tube directly affects the diversity of the microbial communities inside. Studies show that older tubes, between 500 and 800 years old, host a significantly more diverse population of microbes than younger tubes that are less than 400 years old. The process is a form of primary succession, the colonization of a completely new and lifeless habitat.