Microbial mats associated with bryozoans (Coorong Lagoon, South Australia)

Bryostromatolites are laminated carbonate rocks composed of bryozoan zoaria l laminae. The laminated texture is frequently caused by patterns of bryozo an self overgrowth as a regular defensive tactic against microbial fouling. In the Coorong Lagoon (South Australia), another type of bryostromatolite is present where the laminated growth of the weakly calcifying bryozoan spe cies Conopeum aciculata is postmortally stabilized by cyanobacterial mars a t the surface, and fungal mars settling in the zooecial cavities. A tough extracellular slime network produced by benthic cyanobacteria is a trap for sediment particles, provides a method of adhesion to the bryozoan substrate, and produces a biological lamination by the vertical stratificat ion of dead bryozoan skeletons. These slimes are also important for the pre servation of cell structures and for their fossilization. Seasonal fluctuations in salinity and water level are the most important re gional control factors, causing a phase displacement in the growth optima o f microbial mats and bryozoans, thereby resulting in a rigid bryostromatoli tic fabric.