Phospholipid ester-linked fatty acids composition of size-fractionated particles at the top ocean surface

Surface microlayer and subsurface water samples were collected at an oligotrophic Mediterranean site during a diet cycle. The composition of phospholipid ester-linked fatty acids (PLEA) was determined in size-fractionated particles (0.2-0.7 mum; 0.7-200 mum) in order to characterize the major contributors of organic matter to different size fractions. GF/F-retained particles (0.7-200 mum) from the surface microlayer were consistently enriched in PLEA relative to the underlying water. Molecular markers revealed a substantial difference in biological assemblages in both particle sizes. The larger particles were dominated by dinoflagellates, cyanobacteria, microzooplankton and attached bacteria, whereas particles filtered through GF/F and collected on 0.2 mum porosity Durapore filters (0.2-0.7 mum) were mostly bacteria and heterotrophic flagellates. Bacterial PLEA associated with 0.7-200 mum particles were more abundant than those in the 0.2-0.7 mum particles. Specific markers in the branched series appeared more representative of bacteria of smaller particle size. (C) 2004 Elsevier Ltd. All rights reserved.