Formation of phytadienes in the water column: myth or reality?

Since their first identification in marine copepods, phytadienes have been suggested to be biological alteration products of phytol, occurring either as a consequence of grazing of phytoplankton by herbivorous organisms or due to decomposition of plant tissues. In this paper, we report that phytadienes were detected neither in copepods (Temora longicornis) feeding on different species of algae (Rhodomonas sp. and Thalassiosira weissflogii) or on a heterotrophic flagellate (Oxyrrhis marina), nor in their fecal pellets obtained in mesocosm experiments. Two algae (Cryptomonas salina and Peridinium trochoideum), representative phytoplanktons reported to contain phytadienes, were also found to lack these dienes when analyzed using procedures avoiding dehydration reactions. However, phytadienes were observed in the hydrocarbon fractions of C. salina and P. trochoideum when they were exposed to several common analytical treatments (freeze-drying, saponification, acid treatment, etc.). These observations suggest that many reports on the occurrence of phytadienes in the water column may be due to artificial formation of these compounds during common isolation procedures associated with lipids analysis.