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. 20世纪70年代，富营养化（eutrophication）引发的潮间带海草（intertidal seagrasses）大规模衰退后，瓦登海（Wadden Sea）的海草群落呈现分化发展态势。北部瓦登海的海草床（seagrass beds）面积扩张、株丛密度提升，而南部瓦登海仅分布少量株丛密度较低的小型海草床。历史分布记录的缺失阻碍了保护管理工作的推进。不过，北部瓦登海的海草恢复为构建可靠的生境适宜性模型（habitat suitability models）以支撑管理工作提供了契机。
2. 我们基于北部瓦登海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，结合五种机器学习（machine learning）方法，对生境分布模型进行调优。为获取具备地理可迁移性的模型，我们通过非随机空间交叉验证（spatial cross-validation）评估预测精度，并以此为依据对超参数（hyperparameters）进行调优。本研究将空间交叉验证方法与共识建模（consensus modeling）方法相结合。
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）也具有关联，这表明模型实现了收敛，且具备跨空间迁移能力。通过对最优模型的预测结果取平均，进一步提升了预测精度。
4. 我们采用基于适宜性等级的面积校正海草频率（area-adjusted seagrass frequency），以图形化方式分析了共识适宜性评分与训练区域外独立仅存在数据（presence-only data）之间的关联，即连续Boyce指数（continuous Boyce index）。Boyce指数与适宜性评分呈正相关，证明了本次预测方法的合理性。
5. 我们借助连续Boyce指数与生境适宜性评分的关系图，为整个跨国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。该信息对生境保护与修复管理具有重要价值。
6. 预测适宜性与近期实际分布之间的偏差表明，存在未被纳入考量的因素限制了南部瓦登海的海草生长。
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。我们识别出了潮间带海草床能够定植并持续存在的高适宜区域。本研究为动态景观下的高效保护规划提供了科学依据，并确立了监测优先级。