Submarine caves: a laboratory for geomicrobiology studies

Numerous studies have been carried out on microbialite/metazoanassociations and their relative role in forming bioconstructions. It hasoften been suggested that microbial carbonate acts as stabilizing elementof the primary skeletal framework. Here we describe unusualbioconstruction occurring in submerged marine caves. They are randomlydistributed within the caves, and show different sizes and morphologies, aswell as surface roughness/smoothness. These bioconstructions, namedbiostalactites, are constituted by a few cm-thick crust of serpulids andother metazoans associated with carbonate micrites. All the identifiedsessile faunas largely consist of cryptic and sciaphilic organismsindicating cave conditions. Biostalactites are the result of the interactionbetween metazoans and microbial activity. Their distinctive vertical oroblique downward growth from the ceiling and walls of the caves reflectsthe skeletal/microbial relationship. The skeletal framework producedmainly by serpulids is syndepositionally stabilized by autochthonousmicrobial induced micrite.