Isotopic and biochemical composition of Western Mediterranean macroalgae

Among marine primary producers, macroalgae support complex and productive coastal food webs, but coastal primary production relies on terrigenous inputs and remineralized organic matter which both vary seasonally. An approach combining stable isotope and biochemical analyses enables a better characterization of macroalgae specificities and highlights environmental influences on their chemical signature. This study compared the isotopic signature and biochemical composition of 22 Mediterranean macroalgae belonging to Rhodophyta (red algae), Phaeophyceae (brown algae) and Chlorophyta (green algae) between March and November 2010 to capture the differences in species chemical signatures potentially driven by metabolic traits or environmental drivers. Carbon stable isotope values were evidenced as a good proxy of specific carbon metabolism: low values observed in red algae could be related to the reported absence of carbon concentrating mechanisms (CCMs) in this group while higher values were driven by strong CCM activity in green algae. Biochemical patterns also differed between groups: soluble carbohydrates were a major component for red algae, while lipids and proteins dominated in brown algae, and insoluble carbohydrate concentrations were high in green algae. Variation within species across two collection times could be related to environmental changes and algal metabolism. delta N-15 values confirm the efficiency of this parameter as a proxy of the impact of human influence in the Bay of Marseille.