Oxylipin production during a mesocosm bloom of Skeletonema marinoi

Numerous biological activities such as grazer defense and intraspecific signaling have been described for diatom oxylipins, fatty acid derived secondary metabolites produced by some diatom species. As the function and importance of these compounds are still controversial, the production of a subclass of these molecules, nonvolatile oxylipins, was studied during an induced bloom of Skeletonema marinoi (Sarno et Zingone) in a mesocosm setup. Reproductive parameters of one of the main grazers, Calanus finmarchicus, were also examined during the bloom. Oxylipins detected during the bloom were the same as those previously described for S. marinoi and were detected predominantly in the mesocosm inoculated with this diatom. Reproductive success of C. finmarchicus remained unaffected during the course of the bloom. This may have been due to a dilution effect by the availability of alternative suitable prey or to the limited exposure of the copepods to the oxylipins generated during the short bloom. Follow up laboratory studies showed that oxylipin composition changed both when the S. marinoi clone used for inoculation was grown in the laboratory and in comparison to the well-studied Adriatic clone of S. marinoi. These results highlight the necessity of quantitatively measuring oxylipin concentrations during diatom blooms at sea to be able to correctly evaluate their ecological significance.