Data from: A meta-analysis reveals a positive correlation between genetic diversity metrics and environmental status in the long-lived seagrass Posidonia oceanica

The seagrass Posidonia oceanica is a key engineering species structuring coastal marine systems throughout much of the Mediterranean basin. Its decline is of concern, leading to the search for short- and long-term indicators of seagrass health. Using ArcGIS maps from a recent, high-resolution (1-4 km) modelling study of 18 disturbance factors affecting coastal marine systems across the Mediterranean (Micheli et al. 2013), we tested for correlations with genetic diversity metrics (allelic diversity, genotypic/clonal diversity and heterozygosity) in a meta-analysis of 56 meadows. Contrary to initial predictions, weak but significantly positive correlations were found for commercial shipping, organic pollution [pesticides], and cumulative impact. This counterintuitive finding suggests greater resistance and resilience of individuals with higher genetic and genotypic diversity under disturbance (at least for a time) and/or increased sexual reproduction under an intermediate disturbance model. We interpret the absence of low and medium levels of genetic variation at impacted locations as probable local extinctions of individuals that already exceeded their resistance capacity. Alternatively, high diversity at high impact sites is likely a temporal artifact, reflecting the mismatch with pre-environmental impact conditions, especially because flowering and sexual recruitment are seldom observed. While genetic diversity metrics are a valuable tool for restoration and mitigation, caution must be exercised in the interpretation of correlative patterns as found in the present study, because the exceptional longevity of individuals creates a temporal mismatch that may falsely suggest good meadow health status, while gradual deterioration of allelic diversity might go unnoticed.

波西多尼亚海草（Posidonia oceanica）是地中海多数沿岸海域海洋生态系统的关键生态系统工程师物种，其通过生长塑造沿岸海洋系统的结构。该物种的衰退已引发学界广泛关注，促使研究者探寻海草健康状况的短期与长期监测指标。
本研究依托一项针对地中海沿岸海洋系统18种干扰因子的近期高分辨率（1-4千米）建模研究（Micheli等，2013）中的ArcGIS地图，对56处海草床开展元分析，检验遗传多样性指标（包括等位基因多样性、基因型/克隆多样性以及杂合度）与各类干扰因子的相关性。
与初始预测相悖的是，本研究发现商业航运、有机污染（农药类）以及累积干扰与遗传多样性间存在微弱但显著的正相关关系。这一反直觉的发现表明，在干扰条件下（至少在短期内），拥有较高遗传与基因型多样性的海草个体具备更强的抗干扰能力与恢复力；或符合中度干扰模型，即中度干扰下海草的有性繁殖过程会有所增强。
我们将受干扰区域内低、中等水平遗传变异缺失的现象，归因于当地已超出抗干扰阈值的个体发生了局部灭绝。另一方面，高干扰区域内的高遗传多样性可能属于时间尺度上的假象，反映了与干扰前环境条件的错配，这一点尤为突出，因为该物种的开花与有性种群补充现象极少被观测到。
尽管遗传多样性指标是开展海草床生态修复与人类影响减缓的有效工具，但在解读本研究中观测到的相关模式时需格外谨慎：由于海草个体的寿命极长，会产生时间尺度上的错配，可能会错误地暗示海草床健康状况良好；而等位基因多样性的逐步退化则可能被完全忽视。