Sterol composition of steryl chlorin esters (SCEs) formed through grazing of algae by freshwater crustaceans: relevance to the composition of sedimentary SCEs

摘要

In a laboratory experiment, we studied the composition of sterols in steryl chlorin esters (SCEs) egested in fecal pellets of freshwater crustaceans (Daphnia magna and Asellus hilgendorfi) fed on a single green algae (Chlorella, Scendesmus, or Stigeoclonium) or on phytoplankton collected from a shallow pond abundant in diatoms. Both unaltered sterols present in dietary phytoplankton and sterols formed by metabolism in crustaceans were incorporated in the SCEs. C, sterols except for cholesterol (C(27)Delta(5)) and C-28 sterols, major sterols in diatoms, were scarce in the SCEs compared with those in the dietary algae, whereas cholesterol, which could be formed by crustacean metabolism, was relatively abundant in the SCEs. Therefore, the contribution of diatoms to the total phytoplankton population would be underestimated if diatom-specific C, and C, sterols in sedimentary SCEs were used in estimations as biomarkers of diatoms.