Abstract: Fatty acids are sensitive to environmental changes, and have been considered as ecological bioindicators to environmental alterations. It is critical to decipher the traits of lipid remodeling in perennial macroalgae with seasons, which could contribute to understanding how the intertidal macroalgae respond to environmental stresses. We investigated three common macroalgae, including Mazzaella japonica (Rhodophyta), Neorhodomela munita (Rhodophyta) and Ulva lactuca (Chlorophyta), which were distributed in the rocky intertidal zone of the Heishi Reef, Dalian, China. The changes in composition and content of fatty acids in the three macroalgae were compared during February (winter), July (summer), October (fall) 2022, and February (winter) 2023. The fatty acid unsaturation and the content ratio of ω-3/ω-6 fatty acids were further analyzed, while the potential fatty acid biomarkers in each macroalga in response to seasonal variations were uncovered. The results showed that total fatty acid contents and their seasonal fluctuation degrees in the three macroalgae were ranked as M. japonica < N. munita < U. lactuca during February 2022 and February 2023. The content of the total fatty acids in U. lactuca collected on February 2023 was 2.3 and 1.7-fold of that in M. japonica and N. munita, respectively. The total fatty acid contents in all the three macroalgae were high in winter and low in summer, with fatty acid compositions varying with seasons. The relative amounts of the saturated C16:0 and the major ω-6 fatty acids increased significantly in the high temperature season (July), and decreased notably in the low temperature season. The relative abundances of the major ω-3 fatty acids exhibited an opposite variation trend. The fatty acid biomarkers differed from each other in distinct phyla of macroalgae in response to seasonal changes. The saturated C16:0 together with the polyunsaturated C20:4n6 and C20:5n3 was characterized as the potential bioindicators in M. japonica and N. munita (Rhodophyta). Differently, the saturated C16:0 together with the polyunsaturated C16:4n3, C18:3n3 and C18:4n3 was identified as the potential biomarkers in U. lactuca (Chlorophyta). These results provided valuable insights into further understanding the lipid remodeling of intertidal macroalgae in response to seasonal variations, and would facilitate the exploration and utilization of high-quality seaweed resources.

Key words: intertidal zone, macroalgae, fatty acid, lipid remodeling, seasonal variation