STEROLIC BIOMARKERS IN MARINE PHYTOPLANKTON. II. FREE AND CONJUGATED STEROLS OF SEVEN SPECIES USED IN MARICULTURE

Abstract

The sterols of seven unicellular algae widely used in mariculture and belonging to different classes (Prasinophyceae, Haptophyceae, Eustigmatophyceae, and Diatomophyceae) were examined for free and combined forms. Under standard culture conditions, all synthesized free sterols and combined forms (steryl esters, acyl steryl glycosides, and steryl glycosides). Free sterols were dominant in five of the species. In contrast, sterols were mostly esterified in the eustigmatophyte Nannochloropsis oculata (Droop) Hibberd and the diatom Thalassiosira pseudonana Hasle et Heimdal, whereas in another diatom, Chaetoceros calcitrans (Paulsen) Takano, glycosylated forms represented over 60% of total sterols. The pennate diatom Haslea ostrearia (Gaillon) Simonsen synthesized large amounts of steryl glycosides consisting mainly of an unusual sterol, 23,24‐dimethylcholest‐5‐en‐3β‐ol, occurring in some dinoflagellates.