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Analysis of planktonic community structure and trophic interactions using refined isotopic signatures determined by combining fluorescence‐activated cell sorting and isotope‐ratio mass spectrometry
Author(s) -
Pel Roel,
Floris Virgilio,
Hoogveld Hans
Publication year - 2004
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1111/j.1365-2427.2004.01212.x
Subject(s) - phytoplankton , isotopes of carbon , trophic level , zooplankton , population , environmental chemistry , biology , isotope analysis , chemistry , ecology , total organic carbon , nutrient , demography , sociology
Summary 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 carbon sources and sinks in the pelagic food web of Lake Loosdrecht. 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 13 C‐CO 2 in a laboratory confinement, and subsequent monitoring of label transfer to the zooplankton, corroborated selective feeding in some rotifer species. The large‐bodied rotifer Asplanchna , previously thought to be predaceous, apparently mainly fed on algae rather than small rotifers, whereas Euchlanis dilatata actively selected filamentous cyanobacteria. Flow cytometric cell sorting in concert with Py‐GC‐IRMS offers new possibilities in carbon isotope‐based food web studies.