Cyanobacteria of the Wadden Sea: seasonality and sediment influence on community composition

Tidal flats are extremely dynamic habitats in several environmental parameters, which enforces severe selection on their microbial inhabitants. Despite good knowledge of the species present, little is known about the temporal dynamics of their communities. Aim of the study was the investigation of cyanobacterial populations in intertidal flats of the German Wadden Sea and their seasonal- and sediment-type related dynamics of community composition based on next generation sequencing of 16S rRNA fragments. Most of the detected cyanobacterial taxa were present throughout the year, but with changing distribution patterns in different sediment types suggesting migration processes between sediment types during the year. Seasonal as well as tidal changes of environmental conditions and the heterogeneity of the study site concerning grain-size and related parameters created a temporally and spatially highly dynamic ecosystem. Development of microbial mats and community composition was mainly influenced by seasons. The annual mat growth started in spring and reached its maximum in late summer with highest richness as well-stabilized laminated structure. Different grain-sizes provided alternative niches for present taxa when conditions change. Coleofasciculus, Hydrocoleum, and Lyngbya were dominating genera in all sediment types. Βeta diversity of seasonal groups was influenced by the interval between sampling dates.