The role of chemical antifouling defence in the invasion success of Sargassum muticum: A comparison of native and invasive brown algae

Competition and fouling defence are important traits that may facilitate invasions by non-indigenous species. The ‘novel weapons hypothesis’ (NWH) predicts that the invasive success of exotic species is closely linked to the possession of chemical defence compounds that the recipient community in the new range is not adapted to. In order to assess whether chemical defence traits contribute to invasion success, anti-bacterial, anti-quorum sensing, anti-diatom, anti-larval and anti-algal properties were investigated for the following algae: a) the invasive brown alga Sargassum muticum from both, its native (Japan) and invasive (Germany) range, b) the two non- or weak invasive species Sargassum fusiforme and Sargassum horneri from Japan, and c) Fucus vesiculosus, a native brown alga from Germany. Crude and surface extracts and lipid fractions of active extracts were tested against common fouling organisms and zygotes of a dominant competing brown alga. Extracts of the native brown alga F. vesiculosus inhibited more bacterial strains (75%) than any of the Sargassum spp. (17 to 29%). However, Sargassum spp. from Japan exhibited the strongest settlement inhibition against the diatom Cylindrotheca closterium, larvae of the bryozoan Bugula neritina and zygotes of the brown alga F. vesiculosus. Overall, extracts of S. muticum from the invasive range were less active compared to those of the native range suggesting an adaptation to lower fouling pressure and competition in the new range resulting in a shift of resource allocation from costly chemical defence to reproduction and growth. Non-invasive Sargassum spp. from Japan was equally defended against fouling and competitors like S. muticum from Japan indicating a necessity to include these species in European monitoring programs. The variable antifouling activity of surface and crude extracts highlights the importance to use both for an initial screening for antifouling activity.

竞争与防污防御是可能促进非本土物种入侵的关键性状。‘新武器假说’（Novel Weapons Hypothesis, NWH）预测，外来物种的入侵成功与其携带化学防御化合物的能力紧密相关，而这类化合物是新分布区接收群落尚未适应的。为评估化学防御性状是否有助于入侵成功，本研究针对以下藻类开展了抗菌、抗群体感应、抗硅藻、抗幼虫及抗藻类活性检测：a) 入侵性褐藻多产马尾藻（Sargassum muticum），其样本分别采自原生分布区（日本）与入侵分布区（德国）；b) 两种非入侵或弱入侵性藻类——日本产的羊栖菜（Sargassum fusiforme）与海黍子（Sargassum horneri）；c) 德国本土褐藻墨角藻（Fucus vesiculosus）。

研究对粗提物、表面提取物以及活性提取物的脂溶性组分，针对常见污损生物与优势竞争褐藻的合子进行了活性测试。结果显示，本土褐藻墨角藻（Fucus vesiculosus）的提取物可抑制75%的受试细菌菌株，而所有马尾藻属（Sargassum）物种的提取物仅能抑制17%~29%的菌株。然而，日本产的马尾藻属物种对硅藻弯角藻（Cylindrotheca closterium）、总合草苔虫（Bugula neritina）的幼虫以及墨角藻（Fucus vesiculosus）的合子，展现出最强的定居抑制活性。

总体而言，采自入侵分布区的多产马尾藻（Sargassum muticum）提取物的活性低于其原生分布区提取物，这表明该物种在新分布区已适应了更低的污损压力与竞争强度，进而将资源分配从高成本的化学防御转向繁殖与生长。日本产的非入侵性马尾藻属物种对污损生物与竞争者的防御能力与日本产的多产马尾藻相当，这提示有必要将这些物种纳入欧洲的外来物种监测计划。表面提取物与粗提物的抗污损活性存在显著差异，这凸显了在抗污损活性初步筛选中同时使用两类提取物的重要性。