Regional scale patterns in seagrass defences: Phenolic acid content in Zostera noltii

Abstract

Secondary metabolites play an important role in protecting plants from herbivores or pathogens. Despite this, few studies have investigated the presence and the concentration of those compounds over broad spatial scales in seagrasses. Here we analysed the presence and abundance of specific phenolic compounds of Zostera noltii from four different meadows located across the Atlantic and the Mediterranean coast. Three phenolic acids have been found in the samples of Z. noltii: rosmarinic, caffeic and zosteric acids. The proportion of the three compounds varied substantially with the major proportion comprising rosmarinic acid (RA, mean value 94%) followed by zosteric acid (ZA, mean value 4%) and caffeic acid (CAF, mean value 2%). Z. noltii metabolic compounds varied notably between sites. The highest concentrations in RA were found in the Cadiz Bay with values of 11,254 (55 SD) μg g−1 dry wt, while the lowest were observed in the Alfacs Bay (Ebro) with values of 823 (7 SD) μg g−1 dry wt. The highest concentrations in ZA were also observed in the Cadiz Bay with values of 727 (6 SD) μg g−1 dry wt, while the lowest were observed in the Sa Nitja Bay (Menorca Island) with values of 20 (4 SD) μg g−1 dry wt. Finally, the concentrations in CAF remain very low at each site (17–69 μg g−1 dry wt), with the lowest observed in Arcachon. Their proportions remained relatively constant, indicating that most phenolic acids responded together. Documenting the presence of those compounds in living tissues of Z. noltii and how they vary in abundance between seagrass meadows across large geographical scales is a crucial first step to understand the large-scale level response of the plant to potential pathogens, herbivore outbreaks or other ecological processes.