SEASONALITY IN UV-ABSORBING COMPOUNDS OF CYANOBACTERIAL MAT COMMUNITIES FROM AN INTERTIDAL MANGROVE FLAT

Biomass and the concentrations of the W-absorbing compounds scytonemin , pterins and mycosporine-like amino acid compounds (MAAs) were determ ined in a seasonal study of a cyanobacterial mat growing on an interti dal 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 com pact layer on top of the mat without any obvious indication of growth over the course of the study, the latter formed a layer underneath Lyn gbya and showed an increase in the thickness of the layer after the su mmer period. The sheath pigment scytonemin was only formed by L. cf. a estuarii and represented at all sampling dates the quantitatively most important UV-absorbing compound, ranging from 140 to 1300 mg m(-2). T he areal scytonemin content seemed to follow the seasonally fluctuatin g 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 be nthic community underneath.