In this study we examined abiotic and biotic factors that could potentially influence the presence of a non-indigenous seaweed, Eucheuma denticulatum, in two locations, one outside (Kane’ohe Bay, Hawai’i, USA) and one within (Mafia Island, Tanzania) its natural geographical range. We hypothesized that the availability of hard substrate and the amount of wave exposure would explain distribution patterns, and that higher abundance of herbivorous fishes in Tanzania would exert stronger top–down control than in Hawai’i. To address these hypotheses, we surveyed E. denticulatum in sites subjected to different environmental conditions and used generalized linear mixed models (GLMM) to identify predictors of E. denticulatum presence. We also estimated grazing intensity on E. denticulatum by surveying the type and the amount of grazing scars. Finally, we used molecular tools to distinguish between indigenous and non-indigenous strains of E. denticulatum on Mafia Island. In Kane’ohe Bay, the likelihood of finding E. denticulatum increased with wave exposure, whereas on Mafia Island, the likelihood increased with cover of coral rubble, and decreased with distance from areas of introduction (AOI), but this decrease was less pronounced in the presence of coral rubble. Grazing intensity was higher in Kane’ohe Bay than on Mafia Island. However, we still suggest that efforts to reduce non-indigenous E. denticulatum should include protection of important herbivores in both sites because of the high levels of grazing close to AOI. Moreover, we recommend that areas with hard substrate and high structural complexity should be avoided when farming non-indigenous strains of E. denticulatum.

在这项研究中，我们研究了可能影响非本土海藻Eucheuma denticulatum存在的非生物和生物因素，它们分布在两个位置，一个位于外部（美国夏威夷州，凯尼奥赫湾），另一个位于内部（黑手党岛，坦桑尼亚）的自然地理范围。我们假设硬质基质的可用性和波浪暴露的数量可以解释分布模式，并且坦桑尼亚草食性鱼类的丰富度将比夏威夷的自上而下的控制力强。为了解决这些假设，我们在遭受不同环境条件的场所中调查了E. denticulatum，并使用广义线性混合模型（GLMM）来识别E. denticulatum的预测因子。存在。我们还通过调查放牧疤痕的类型和数量来估计草食性大肠杆菌的放牧强度。最后，我们使用分子工具来区分黑手党岛上的E. denticulatum的本地和非本地菌株。在Kane'ohe湾，发现的可能性E.蟹与波暴露增加，而上马菲亚岛岛的可能性珊瑚瓦砾盖增大，从导入（AOI）的区域随距离减少，但这种减少不太明显在珊瑚瓦砾的情况下。卡内奥赫湾的放牧强度高于黑手党岛。但是，我们仍然建议努力减少非本地的E. denticulatum由于靠近AOI的高放牧水平，应该在两个地点都包括重要草食动物的保护。此外，我们建议在种植非土生的E. denticulatum菌株时，应避免使用具有坚硬底物和高结构复杂性的区域。