How many mite species dwell in subterranean habitats? A survey of Acari in Belgium

Underground compartments are one of the least known environments in the world. In our study we collected 137 samples, using different techniques, in 30 caves and other cavities (mine galleries, underground chalk quarries, superficial underground compartments – SUC and resurgences). In total 814 individuals of mites were collected, representing 99 taxa from 43 families. Eighty-three species were added to the list of mite speleofauna in Belgium; the highest number of new species for underground environments was noted for Mesostigmata. Four mite species were classified as obligate cave dwellers. We also made an extrapolated estimate of the number of species in subterranean habitats in Belgium. The fauna of the superficial underground compartments was distinct with 60% of species typical of underground compartments. In most cavities accessible for tourists and artificial cavities high number of mites was observed. Additionally, the importance of using different sampling methods to recognize biodiversity in a subterranean biome were discussed.