Abstract
Macroalgae constitute one of the preferred substrates of the benthic dinoflagellate Ostreopsis cf. ovata. Across the Mediterranean Sea, this toxic microalga has been shown to thrive on the surface of various species of macroalgae, including Chlorophyta, Rhodophyta and Phaeophyceae. Interestingly, some Dictyotaceae are characterized by a low abundance of cells of O. cf. ovata on their surface. Based on the antifouling properties of some specialized metabolites produced by seaweeds, macroalgal metabolites have been proposed to contribute to the settlement and development of O. cf. ovata. To address this question, the composition of the surface of four Dictyotaceae, Dictyota dichotoma, Dictyota spiralis, Taonia atomaria and Padina pavonica was investigated through an integrative approach combining the analysis of their eukaryotic diversity (18S rRNA gene metabarcoding), their surface metabolome (untargeted LC-MS-based metabolomics) as well as the bioactivity of their surface extracts on O. cf. ovata. Altogether, the data suggest an influence of the macroalgal surface chemistry on the growth of the dinoflagellate, with D. dichotoma being the most bioactive. Some metabolites are proposed to be involved in the observed bioactivity. Other biotic factors are also likely to be entailed in the control of the O. cf. ovata population and they may even prevail on the influence of the macroalgal surface chemistry.
Highlights
Recurrent outbreaks of the toxic dinoflagellate Ostreopsis cf. ovata have been reported over the past 15 years in Mediterranean coastal waters (Ciminiello et al, 2006; Mangialajo et al, 2011)
This study aims to investigate the influence of the surface metabolome of four brown algae of the Dictyotaceae family (T. atomaria, P. pavonica, D. dichotoma, and Dictyota spiralis) on the settlement of the toxic dinoflagellate O. cf. ovata in the NW Mediterranean
Post hoc analysis revealed a significantly higher concentration of cells on D. dichotoma compared to D. spiralis and P. pavonica, while no significant differences were detected between T. atomaria, P. pavonica, and D. spiralis, and neither between T. atomaria and D. dichotoma – due to one outlier sample
Summary
Recurrent outbreaks of the toxic dinoflagellate Ostreopsis cf. ovata have been reported over the past 15 years in Mediterranean coastal waters (Ciminiello et al, 2006; Mangialajo et al, 2011). Role of Macroalgal Surface Metabolites that colonizes a variety of substrates, including macrophytes (Totti et al, 2010; Mangialajo et al, 2011). The surface of these seaweeds can constitute an ideal microenvironment for the growth of highly diverse prokaryotic and eukaryotic communities, including benthic microalgae. Several metabolites produced by species of the family Dictyotaceae have been shown to inhibit the growth of bacteria (e.g., dictyol C and fucoxanthin; Salvador Soler et al, 2007; Viano et al, 2009), microalgae (e.g., dictyolactone and sanadaol; Kim et al, 2006), bryozoan (e.g., dictyol E, pachydictyol A, dictyodial; Schmitt et al, 1998) and various other benthic species (e.g., diterpenoids, gleenol, and geranylgeranylglycerol; Bianco et al, 2009; Othmani et al, 2016b)
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