Diatom induction of reproductive failure in copepods: The effect of PUAs versus non volatile oxylipins

Several species and strains of diatoms were tested for their effects on egg production, hatching success, faecal pellet production, ingestion rate and food selection in the copepod Temora stylifera. Two of the diatom species tested were well known polyunsaturated aldehyde (PUA) producers: Skeletonema marinoi (SM) and Thalassiosira rotula (TR1), while the other species tested, Skeletonema pseudocostatum, was a non-PUA producing species. Another T. rotula strain (TR2) was also tested since previous studies had reported contradictory results, due either to absence of PUA production or production in small amounts. Our results showed strong inhibitory effects on reproductive parameters of copepods with all diatom species tested. Although we confirm that S. pseudocostaum did not produce PUAs, this diatom produced large quantities of other oxylipins such as (5Z,8Z,11Z,13E,15S,17Z)-15-hydroxy-5,8,11,13,17-eicosapentaenoic acid (15S-HEPE) and 13,14-13R-hydroxy-14S,15S-trans-epoxyeicosa-5Z,8Z,11Z,17Z-tetraenoic acid (13,14-HEpETE) and 15- oxo-5Z,9E,11E,13E-pentadecatetraenoic acid (15-oxoacid), all of which have already been found in S. marinoi (Fontana et al., 2007a) and Pseudonitzschia delicatissimia (d'Ippolito et al., 2009). Another unidentified oxylipin was also present in high quantities in LC–MS profiles. Some of these oxygenated fatty acid derivatives were also found, together with PUAs, in TR1 and in TR2. Both PUA-producing and non-producing diatoms caused negative effects on hatching success with induction of apoptosis in newly hatched nauplii. This suggests that negative diatom effects can also depend on the production of non volatile oxylipins. Copepod feeding behaviour was found to be non-selective when each diatom species was offered together with the non toxic dinoflagellate Prorocentrum minimum suggesting that grazers are not aware of the toxicity of their food.