CONICET | Buscador de Institutos y Recursos Humanos

Microbial mats play a paramount role in sediment biostabilization in tidal flats. Sporadic storms affect the microbial mat surface in the upper intertidal-lower supratidal zone of Bahía Blanca estuary (Argentina), forming characteristic structures. When this occurs, the underlying siliciclastic sediment is exposed by erosion or disruption of the mat cover, and in a lapse of few weeks a new microbial community establishes. The objective of this experiment was to study recolonization patterns and the ecological succession of microorganisms at the (micro)scale of these erosional structures. Field experiments consisted in the removal of the microbial mat layer (~2 cm) in a square area of 225 cm2 to simulate an erosional structure. In turn, this quadrat was subdivided into 84 equidistant sampling points, and cylindrical sediment cores (6 mm diameter, 3 mm height) were randomly taken every 3-4 days for 6 weeks. Sampling was consistently done during low tide at daytime. The microorganisms from core samples (e.g. diatoms, cyanobacteria, dinoflagellates), were enumerated by microscopy. The pattern evidenced an initial rapid colonization, mostly by motile pennate diatoms (e.g. Navicula phyllepta, Nitszchia palea, Cylindrotheca closterium), and a few centric diatoms (e.g. Melosira). During this initial phase, cell numbers increased 6-fold in 7-d from an initial density of ~0.25 × 106 cells cm-3. Cell numbers continued increasing, until reaching values in the order of 3-4.5 × 106 cells cm-3. Filamentous cyanobacteria (e.g. Oscillatoria and Arthrospira) took longer than diatoms to colonize the denuded sediment and only appeared in later stages (day 10 onwards). However, in the time monitored after remotion of the original mat (i.e. 56-d) the presence of cyanobacteria species indicative of mature microbial mats (e.g. Microcoleus chthonoplastes) was not observed. The dominance of pennate diatoms over other groups