Coastal ecosystem functioning often hinges on habitat-forming foundation species that engage in positive interactions (e.g. facilitation and mutualism) to reduce environmental stress. Seagrasses are important foundation species in coastal zones but are rapidly declining with losses typically linked to intensifying global change-related environmental stress. There is growing evidence that loss or disruption of positive interactions can amplify coastal ecosystem degradation as it compromises its stress mitigating capacity. Multiple recent studies highlight that seagrass can engage in a facultative mutualistic relationship with lucinid bivalves that alleviate sulphide toxicity. So far, however, the generality of this mutualism, and how its strength and relative importance depend on environmental conditions, remains to be investigated. Here we study the importance of the seagrass-lucinid mutualistic interaction on a continental-scale using a field survey across Europe. We found that the lucinid bivalve Loripes orbiculatus is associated with the seagrasses Zostera noltii and Zostera marina across a large latitudinal range. At locations where the average minimum temperature was above 1 °C, L. orbiculatus was present in 79% of the Zostera meadows; whereas, it was absent below this temperature. At locations above this minimum temperature threshold, mud content was the second most important determinant explaining the presence or absence of L. orbiculatus. Further analyses suggest that the presence of the lucinids have a positive effect on seagrass biomass by mitigating sulphide stress. Finally, results of a structural equation model (SEM) support the existence of a mutualistic feedback between L. orbiculatus and Z. noltii. We argue that this seagrass-lucinid mutualism should be more solidly integrated into management practices to improve seagrass ecosystem resilience to global change as well as the success of restoration efforts.

中文翻译：

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兼性互利共生促进了欧洲海草草甸

沿海生态系统的功能通常取决于栖息地形成的基础物种，这些物种参与积极的互动（例如促进和共生）以减少环境压力。海草是沿海地区重要的基础物种，但正在迅速减少，损失通常与加剧的全球变化相关的环境压力有关。越来越多的证据表明，积极相互作用的丧失或破坏会加剧沿海生态系统的退化，因为它会损害其缓解压力的能力。最近的多项研究强调，海草可以与 lucinid 双壳类动物建立兼性互惠关系，从而减轻硫化物的毒性。然而，到目前为止，这种互利共生的普遍性，以及它的强度和相对重要性如何取决于环境条件，仍有待研究。在这里，我们使用欧洲的实地调查研究大陆尺度上海草-灵芝互惠相互作用的重要性。我们发现，lucinid 双壳类动物Loripes orbiculatus在很大的纬度范围内与海草Zostera noltii和Zostera marina相关。在平均最低温度高于 1 °C 的地方，L. orbiculatus存在于 79% 的Zostera草甸中；而低于此温度则不存在。在高于此最低温度阈值的位置，泥浆含量是解释 L. orbiculatus 存在与否的第二重要决定因素。进一步的分析表明，lucinids 的存在通过减轻硫化物胁迫对海草生物量产生积极影响。最后，结构方程模型 (SEM) 的结果支持之间存在互惠反馈L. orbiculatus和Z. noltii。我们认为，这种海草-灵芝共生应该更牢固地融入管理实践中，以提高海草生态系统对全球变化的适应能力以及恢复工作的成功。