Temperature impact on the trophic transfer of fatty acids in the congeneric copepods Acartia tonsa and Acartia clausi

• Temperature impact on the FA profile of Acartia tonsa and A. clausi was determined.
• Elevated temperature enlarged the storage lipid content in both species.
• DHA and EPA in membrane lipids were higher in A. clausi compared with A. tonsa.
• The membrane FA of A. tonsa changed profoundly in response to temperature.
• Replacement of A. clausi by A. tonsa appears detrimental for next trophic level.

Copepods of the genus Acartia occur worldwide and constitute an important link to higher trophic levels in estuaries. However, biogeographical shifts in copepod assemblages and colonization of certain European estuaries by the invader A. tonsa, both driven or enhanced by increasing ocean temperature, raise the pressure on autochthonous copepod communities. Despite the profound effect of temperature on all levels of biological organization, its impact on the fatty acid (FA) dynamics of Acartia species is understudied. As certain FAs exert a bottom-up control on the trophic structure of aquatic ecosystems, temperature-induced changes in FA dynamics of Acartia species may impact higher trophic levels. Therefore, this study documents the short-term temperature responses of A. tonsa and A. clausi, characterized by their warm- versus cold-water preference respectively, by analyzing the FA profiles of their membrane and storage lipids under 5 and 15 °C. Copepods that were fed an ad libitum diet of the diatom Thalassiosira weissflogii (bloom conditions) under 15 °C increased their storage FA content substantially. Furthermore, the membrane FA composition of A. tonsa showed a more profound temperature response compared with A. clausi which might be linked with the eurythermal character of the former.