AME 82:253-264 (2019)  -  DOI: https://doi.org/10.3354/ame01895

ABSTRACT: Stromatolites, structures formed with the input of microorganisms such as cyanobacteria, can be traced back to the Precambrian. Many modern marine stromatolites have a coarser internal structure and host a diverse eukaryotic community. Known as eualgal-cyanobacterial stromatolites, these formations are likely a result of the higher abundance of larger sediment particles from the biomineralisation of skeletal material. However, it is unclear how eukaryotic microalgae have contributed towards modern stromatolite formation. Therefore, the aim of this study was to investigate how the microalgal community contributes towards the differences in depth profiles and layering observed amongst mesofabric structures in stromatolite pools along the Port Elizabeth coastline in South Africa. This goal was achieved by comparing the proportional abundances of each of the major microalgal classes (cyanobacteria, bacillariophytes and chlorophytes) between the different mesofabric types and depth profiles. Clear variability in terms of proportional abundance was apparent between microhabitats and with depth. Coarser, irregular types had a higher bacillariophyte biomass than smoother types. This difference is likely a consequence of the greater efficiency of bacillariophytes in trapping larger sediment particles. Eukaryotic microalgae (specifically bacillariophytes) are highlighted as important ecosystem engineers in these modern ecosystems.

KEY WORDS: Microbialites · Mesofabric types · Niches · Microphytobenthos · Ecosystem engineering