Impact of the diatom oxylipin 15S-HEPE on the reproductive success of the copepod Temora stylifera

The copepod Temora stylifera was fed with the pennate diatom Pseudo-nitzschia delicatissima for 15 days. This diatom does not produce polyunsaturated aldehydes (PUAs) but only synthesizes other oxylipins such as the hydroxyacid (5Z,8Z,11Z,13E,15S,17Z)-15-hydroxy-5,8,11,13,17-eicosapentaenoic acid (15S-HEPE). Effects of this monoalgal diet were compared to copepods fed with the PUA-producing diatom Skeletonema marinoi and the control dinoflagellate Prorocentrum minimum which does not produce any oxylipins. Both egg production and hatching success were negatively affected by the two diatoms compared to the control diet. Both diatoms also induced malformations in the offspring, with the number of malformed nauplii increasing dramatically with time. Malformed nauplii were apoptotic (TUNEL-positive) indicating imminent death. In terms of recruitment, only 4 healthy nauplii female⁻¹ day⁻¹ with S. marinoi and 9 healthy nauplii female⁻¹ day⁻¹ with P. delicatissima were produced during the 15-day experimental period. The results indicate that P. delicatissima induced negative effects comparable to those of S. marinoi even though it did not produce PUAs. This is the first study that tests the biological activity of oxylipins other than PUAs on copepod reproduction.