Formation of laminated cyanobacterial mats in the absence of benthic fauna

Illuminated, defaunated shallow-water sediments develop cyanobacterial mats that in most details resemble stromatolitic mats previously described from hyperhaline habitats. These artificial mats grow continuously, increasing about 2 mm in thickness per year. The cyanobacterial mats are completely destroyed within 1 to 2 wk after colonisation by benthic animals. Specific representatives of the meiofauna and the macrofauna disrupt and ingest the cyanobacterial mars; bioturbation by larger animals also destroys the simple 1-dimensional vertical zonation patterns characteristic of microbial mats and thus their structural and functional integrity. The findings support the hypothesis that fossil stromatolites are rare in Phanerozoic deposits due to the activities of benthic animals which originated in the late Precambrian.