Data from: Consensus forecasting of intertidal seagrass habitat in the Wadden Sea

1. After the dramatic eutrophication-induced decline of intertidal seagrasses in the 1970s, the Wadden Sea has shown diverging developments. In the northern Wadden Sea seagrass beds have expanded and gotten denser while in the southern Wadden Sea only small beds with low shoot densities are found. A lack of documentation of historical distributions hampers conservation management. Yet, the recovery in the northern Wadden Sea provides opportunity to construct robust habitat suitability models to support management. 2. We tuned habitat distribution models based on 17 years of seagrass surveys in the northern Wadden Sea and high-resolution hydrodynamics and geomorphology for the entire Wadden Sea using five machine learning approaches. To obtain geographically transferable models, hyperparameters were tuned on the basis of prediction accuracy assessed by non-random, spatial cross-validation. The spatial cross-validation methodology was combined with a consensus modeling approach. 3. The predicted suitability scores correlated amongst each other and with the hold-out observations in the training area indicating that the models converged and were transferable across space. Prediction accuracy was improved by averaging the predictions of the best models. 4. We graphically examined the relationship between the consensus suitability score and independent presence-only data from outside the training area using the area-adjusted seagrass frequency per suitability class (continuous Boyce index). The Boyce index was positively correlated with the suitability score indicating the adequacy of the prediction methodology. 5. We used the plot of the continuous Boyce index against habitat suitability score to demarcate three habitat classes - unsuitable, marginal and suitable - for the entire international Wadden Sea. This information is valuable for habitat conservation and restoration management. 6. Divergence between predicted suitability and actual distributions from the recent past indicates that unaccounted factors limit seagrass development in the southern Wadden Sea. 7. Synthesis and applications. Our methodology and data enabled us to produce a robust and validated consensus habitat suitability model. We identified highly suitable areas where intertidal seagrass meadows may establish and persist. Our work provides scientific underpinning for effective conservation planning in a dynamic landscape and sets monitoring priorities.

1. 二十世纪七十年代，富营养化（eutrophication）引发的潮间带海草（intertidal seagrass）大规模衰退后，瓦登海（Wadden Sea）的海草群落呈现分化发展态势。瓦登海北部的海草床（seagrass beds）持续扩张且密度提升，而南部仅分布少量植株密度较低的小型海草床。历史分布记录的缺失，阻碍了相关保护管理工作的推进。不过，瓦登海北部的海草恢复为构建可靠的生境适宜性模型以辅助管理提供了契机。
2. 本研究基于瓦登海北部17年的海草调查数据，以及覆盖整个瓦登海的高分辨率水动力学（hydrodynamics）与地貌学（geomorphology）数据，通过五种机器学习方法（machine learning approaches）优化生境分布模型。为获得具备地理迁移性的模型，研究采用非随机空间交叉验证（spatial cross-validation）评估预测精度，并以此调整超参数；同时将空间交叉验证方法与共识建模（consensus modeling）手段相结合。
3. 预测得到的适宜性评分彼此间存在相关性，且与训练区域内的预留观测样本（hold-out observations）同样存在关联，这表明模型具备收敛性且可跨空间迁移。通过对最优模型的预测结果进行平均集成，进一步提升了预测精度。
4. 本研究基于每类适宜性等级的面积校正海草频率，绘制了针对训练区域外独立仅存在数据（presence-only data）的连续博伊斯指数（continuous Boyce index）与共识适宜性评分的关系图，以此分析二者关联。结果显示，博伊斯指数与适宜性评分呈正相关，证实了本预测方法的有效性。
5. 本研究借助连续博伊斯指数与生境适宜性评分的对应关系，为整个国际管辖范围内的瓦登海划定了三类生境等级：不适宜生境、边缘适宜生境与适宜生境。该成果可为海草生境保护与修复管理提供重要支撑。
6. 预测适宜性分布与近期实际分布之间存在差异，说明仍有未被纳入考量的因素限制了瓦登海南部的海草群落发展。
7. 总结与应用：本研究的方法与数据支撑我们构建了可靠且经过验证的共识生境适宜性模型，识别出了潮间带海草草原能够定植并持续存续的高适宜区域。本研究为动态景观下的高效保护规划提供了科学依据，并确立了优先监测方向。