Plankton sampling during a recent cruise in the Sargasso Sea provided
numerous gelatinous macrozooplankton (salps) whose large gut contents
afforded an opportunity to investigate the formation of phorbin steryl
esters (PSEs) during zooplankton grazing. Sufficient material was obt
ained from about 50 salps to allow detailed determination of distribut
ions and carbon stable isotope compositions of free sterols and PSE-st
erols. Phorbin steryl esters were abundant in the gut contents of the
salps but were absent from a large volume (80001) sample of suspended
particulate matter (SPM), the presumed dietary material of the salps.
Free sterols in salp gut contents and in SPM had similar isotopic rati
os suggesting that indeed the sterols in SPM might be a major source o
f sterols in the gut contents, but PSE-sterols were enriched in C-13 b
y 1-2 parts per thousand compared to free sterols, indicating a trophi
c fractionation during PSE formation. These results further strengthen
the role of zooplankton grazing on phytoplankton in PSE production. C
opyright (C) 1996 Elsevier Science Ltd.