Seasonality in UV-absorbing compounds of cyanobacterial mat communities from an intertidal mangrove flat

Biomass and the concentrations of the UV-absorbing compounds scytonemin, pterins and mycosporine-like amino acid compounds (MAAs) were determined in a seasonal study of a cyanobactenal mat growing on an intertidal mangrove sediment at Towra Point, Sydney, Australia. The community was dominated by the filamentous cyanobacteria Lyngbya cf. aestuarii and Microcoleus chthonoplastes. While the first occurred as a thin compact layer on top of the mat without any obvious indication of growth over the course of the study, the latter formed a layer underneath Lyngbya and showed an increase in the thickness of the layer after the summer period. The sheath pigment scytonemin was only formed by L. cf. aestuarii and represented at all sampling dates the quantitatively most important UV-absorbing compound, ranging from 140 to 1300 mg m^-2. The areal scytonemm content seemed to follow the seasonally fluctuating solar intensity. In contrast, the areal contents of pterins and MAAs did not increase under elevated solar radiation conditions. The data indicate the importance and effectiveness of scytonemin deposition in the outer sheaths of L. cf. aestuarii as a sunscreen for the entire benthic community underneath.