Introduced macroalgae becoming invasive may alter ecological functions and habitats in recipient ecosystems. In the Western Indian Ocean (WIO), non-native strains of the native macroalgae Eucheuma denticulatum were introduced for farming practices and consequently spread into the surrounding seascape. We investigated potential effects of non-native and native strains of this macroalgae on a branching coral. We conducted a four-factor field experiment where we examined growth and holdfast development of introduced and native E. denticulatum on live and dead branches of Acropora sp. in the presence and absence of herbivores in Unguja Island, Zanzibar. Moreover, we estimated coral and macroalgae condition by visual examinations, gene expression analyses, and photosynthetic measurements. Macroalgae did not attach to any live coral and coral condition was not impacted by the presence of E. denticulatum, regardless of geographical origin. Instead, necrotic tissue on the macroalgae in areas of direct contact with corals indicated damage inflicted by the coral. The biomass of E. denticulatum did not differ between the replicates attached to live or dead corals in the experiment, yet biomass was strongly influenced by herbivory and replicates without protection from herbivores had a significantly lower biomass. In the absence of herbivory, introduced E. denticulatum had significantly higher growth rates than native algae based on wet weight measurements. These results contribute to an increased understanding of environmental effects by the farming of a non-native strain of algae on corals and stresses the importance to maintain viable populations of macroalgal feeding fishes in such areas.

引入的大型藻类变得具有入侵性，可能会改变接受者生态系统中的生态功能和栖息地。在西印度洋 (WIO)，本地大型藻类Eucheuma denticulatum 的非本地菌株被引入用于农业实践，并因此传播到周围的海景中。我们研究了这种大型藻类的非本地和本地菌株对分枝珊瑚的潜在影响。我们进行了四因素田间试验，我们检查的增长，并介绍和本地的固着器发展E.蟹的存活和死亡的分支鹿角sp. 桑给巴尔温古贾岛是否存在食草动物。此外，我们通过目视检查、基因表达分析和光合作用测量来估计珊瑚和大型藻类的状况。大型藻类不附着在任何活珊瑚上，珊瑚状况不受E. denticulatum存在的影响，无论地理来源如何。相反，与珊瑚直接接触的大型藻类上的坏死组织表明珊瑚造成了损害。E. denticulatum的生物量在实验中附着在活珊瑚或死珊瑚上的复制品之间没有差异，但生物量受到食草动物的强烈影响，并且没有食草动物保护的复制品的生物量显着降低。在没有食草动物的情况下，引入根据湿重测量，E. denticulatum 的生长速度明显高于原生藻类。这些结果有助于通过在珊瑚上养殖非本地藻类来加深对环境影响的理解，并强调在这些地区维持可食用的大型藻类鱼类种群的重要性。