STERYL CHLORIN ESTERS ARE FORMED BY ZOOPLANKTON HERBIVORY

Steryl chlorin esters (SCEs) were formed in laboratory feeding experim ents when starved females of the copepod Calanus helgolandicus were al lowed to graze on a culture of the diatom Thalassiosira weissflogii. T hey were found when the zooplankton had grazed for 48 hours and were a lso identified in fecal pellets subsequently left in seawater in the d ark. The distribution contained the diatom sterols in approximately th e same relative abundance as the free sterols in the substrate, as wel l as the most abundant copepod sterol, all esterified to the chlorophy ll a degradation product, pyropheophorbide a. Hence, in studies aimed at using sedimentary SCE sterol distributions as indicators of phytopl ankton community structure, cholesterol should not be considered since the cholesteryl ester of pyropheophorbide a was a significant compone nt in the fecal pellet SCEs. The findings represent a step forward in unravelling the transformations undergone by chlorophyll a in aquatic environments, since the abundance and wide occurrence of sedimentary S CEs indicate that they are a significant preservational sink for the c hlorophyll a biosynthesised in the photic zone.