Energy transfers in a predator–prey context involving D. salina (microalga), F. salina (ciliate) and A. salina (crustacean), living in salterns of Sfax (Tunisia)

Dunaliella salina (microalgae), Fabrea salina (ciliate) and Artemia salina (crustacean) are the most abundant halophile Eukaryote organisms present in solar salterns at Sfax (Tunisia) when salinity is up to 150 PSU. We analysed the predator/prey relationship between the three organisms in laboratory conditions. In this study, aquatic food web relations were analysed by studying the grazing and energy transfer rates. In solar saltern, the dynamic population of Dunaliella displays a negative relationship with that of Fabrea and Artemia. Grazing experiments confirm that Fabrea and Artemia exercise a top-down control on Dunaliella populations. While Artemia and Fabrea occupy the same trophic level in food chain, the grazing rate of Fabrea on Dunaliella is strongly high reaching 0.85 × 10⁶ ± 0.05 cells mL⁻¹ day⁻¹. The fatty acids (FAs) appeared as good tracers to define the energy transfer along the food chain studied. Effectively, the FA composition of consumers appeared correlated to the FA of their prey. In parallel, the saturated fatty acids (SFAs) content decreased according to the trophic levels, and the opposite was observed for monounsaturated fatty acids (MUFAs). Therefore, palmitic acid (C16:0) showed trends that rendered it useful for tracing trophic transfer to consumers (Artemia). The polyunsaturated fatty acid (PUFA) and especially linoleic acid (C18:2) and linolenic acid (C18:3) were able to be traced across the transfer to Fabrea. This study increased our knowledge of the energy transfer between the major halophile organisms living in the solar salterns at Sfax (Tunisia). We proposed also that the fatty acids are used in future investigations to understand the predator/prey ecological relationship in marine eukaryote organisms.