LB 20-181 - Amino acid specific isotope ratios in macroalgae reveal environmental changes: the potential as eco-physiological biomarker

Macroalgae are crucial ecosystem components that inform the environmental change and its impacts on basis of marine food webs. However, the large variations of stable isotope ratios in marine producers have hindered our understanding of their ecological functions, therefore their physiological response to environmental conditions need to be elucidated. Herein, we tested (1) the magnitude of stable isotope variation of bulk and individual amino acids (AA) in macroalgae in response to environmental conditions such as seasonality and diverse lab settings by using perennial Ecklonia and ephemeral Ulva species and (2) its effects on ecosystem analysis. Results showed that δ15N values of bulk and most AAs in Ecklonia were affected by seasonal variation, while δ13C and δ15N differences of glutamic acid and phenylalanine (also known as b-value) were similar throughout seasons. Moreover, Ulva culture under N addition for 2 weeks showed low δ15N value in overall temperature ranges, but its bulk δ13C, C:N ratio, AA specific δ13C ratios became higher with temperature change from 12 °C to 27.5 °C. Nonetheless, the δ13C variability pattern of essential AAs (Valine, Leucine, Isoleucine, Threonine, Phenylalanine) in overall macroalgae was effective to show a trophic link of grazer Caprella with the co-occurring macroalgae in situ collected from the same habitat. These findings suggest that AA isotope variations can reflect the drastic environmental changes, particularly where bulk stable isotope analysis alone is insufficient. Macroalgal based AA isotope variation also provides valuable eco-physiological insights to characterize the local habitats for potential application in ecosystem surveys.