A biogeochemical study of the Abu Dhabi algal mats: A simplified ecosystem

Abstract

A variety of lipid classes (alkanes, alkenes, carboxylic acids, carotenoids, saturated alcohols, sterols and stanols) in a core from an intertidal, tropical algal mat (Abu Dhabi, Persian Gulf) have been analysed. The n-alkanes and n-alkanoic acids maximise at n-C17 and n-C16, respectively, and show little or no contribution from homologues > C20. No evidence of pollution from petroleum products is apparent in the branched/cyclic alkanes, which have a simple distribution and contain the unresolved mixture of 7- and 8-methylheptadecanes as a relatively abundant component. Among the major carotenoids, components assigned as β-carotene, torulene, echinenone, spirilloxanthin, rhodopin, 3,4-dehydrorhodopin, zeaxanthin and myxoxanthophyll were present. The distributions of these classes show little or no evidence of a higher-plant contribution and are compatible with the most abundant micro-organisms identified in the core, viz., Lyngbya aestuarii and Microcoleus chthonoplastes (blue-greens), and Chromatium and Thiocystis spp. (purple photosynthetic bacteria). The presence of torulene suggests fungal activity.Only Δ5 or Δ5,22 sterols were observed and their distributions cannot be related at present to specific inputs. However, the distributions of all of the compound classes show features which have been observed in similar analyses of other blue-green algal mat situations.