Gaoge Wang

Anti‐epiphyte defences in the red seaweed Gracilaria vermiculophylla: non‐native algae are better defended than their native conspecifics

Summary 1.Epibiosis in the marine environment is a stressor that may determine invasion success in introduced species. Previous comparisons showed resistance to epibionts can be higher in non-native than in resident seaweed species, but we do not know whether it is an intrinsic trait of the non-natives or it has been acquired during the invasion process. To elucidate this question, a comparison between native and non-native populations of the same species is needed. 2.Resistance against two groups of epiphytes was assessed in living thalli and in artificial substrata coated with surface extracts, both gained from four Asian (native) and four European (non-native) populations of the red alga Gracilaria vermiculophylla. Two diatom species and two filamentous macroalgae were used as micro- and macro-epiphytes, and one of each type was collected in Asia, while the other came from Europe. Laboratory assays were done in both distributional ranges of G. vermiculophylla and in different seasons. We used G. vermiculophylla from four populations in each range and used a fully-crossed design with the factors a) ‘Origin of Gracilaria’, b) ‘Origin of epiphytes’, c) ‘Season’ and d) ‘Solvent used for extraction’. 3.Both groups of epiphytes, regardless of their origin, attached less to living thalli and to surface extracts from non-native G. vermiculophylla. Fewer diatoms attached to hexane-based extracts, while fewer Ceramium filaments settled on extracts gained with dichloromethane. 4.Synthesis. Our results show for the first time that non-native individuals of a marine organism are better defended against epiphytes than native conspecifics. Furthermore, we found evidence that at least a part of the defense is based on extractable secondary metabolites. We discuss several mechanisms that could explain the increased resistance to epiphytes in non-native individuals, including the release from enemies in the non-native range, which could lead to an increase in algal performance during the invasion process. We suggest that an enhanced defense against epiphytes after introduction is one reason for G. vermiculophyllas invasion success. Our observation may also apply to other basibiont-epibiont and host-enemy systems, including plant-plant, plant-animal and animal-animal interactions, in aquatic environments and could be a key feature of bioinvasions. This article is protected by copyright. All rights reserved.