1. Thermally assisted hydrolysis and methylation of cellular lipids, by means of Curie-point pyrolysis of intact whole cells in the presence of a quaternary ammonium hydroxide reagent, provided analytical access (pyrolysis-gas chromatography; Py-GC) to the very small amounts of algal carbon delivered by fluorescence-activated cell sorting. Based on differences in pigment composition, population-specific in situ fatty acid profiles could be obtained of the major taxa present in the phytoplankton of Lake Loosdrecht (The Netherlands). 2. By combining Py-GC and compound-specific isotope-ratio mass spectrometry (Py-GC-IRMS) the in situ carbon isotopic signatures could be established of the fatty acid profiles retrieved by flow cytometry. Colonial phytoplankton not amenable to cell sorting and zooplankton specimens were also isotopically characterised with this technique by subjecting handpicked samples to pyrolytic methylation. In this way proxies could be obtained in great detail for isotopic end-members delineating important 3. These analyses suggested a significant isotopic heterogeneity among major representatives of the phytoplankton in Lake Loosdrecht. This heterogeneity was also reflected in the isotopic composition of the zooplankton, implying the occurrence of preferential grazing. A differential labelling of the phytoplankton using 13C-CO2 in a laboratory confinement, and subsequent monitoring of label transfer to the zooplankton, corroborated selective feeding in some rotifer species. The large-bodied rotif [KEYWORDS: cell sorting; fatty-acid; biomarker; plankton analysis; pyrolytic methylation; stable isotopes]
Original languageEnglish
JournalFreshwater Biology
Journal publication date2004

ID: 77753