Rapid urbanization leads to an accelerating decline of seagrass beds. The status of seagrass beds along the entire coastline of a rapidly urbanizing area, Guangdong Province, was examined to document the change in seagrass beds and to explore the determinants of seagrasses characteristics and their plasticity. Thirteen seagrass beds were newly discovered with a total area as 679.04 ha, whereas eleven known seagrass beds have decreased from 972.55 ha to 858.67 ha with seven of them having disappeared in recent decade primarily due to exacerbated construction of artificial shorelines and beach dams, increased nutrient inputs from fish caging and shrimp pond culture, oyster culture, mangrove planting and shellfish collection. The leaf nitrogen content of Halophila ovalis, which dominated the largest beds, increased from (2.09 ± 0.24)% in 2011 to (3.39 ± 0.18)% in 2017, indicating enhanced eutrophication. The optimum seawater dissolved inorganic nitrogen and dissolved inorganic phosphorus levels for Halophila beccarii were 40 μmol/L and 2.5 μmol/L, respectively. The standing stock and plant dimensions of H. beccarii were positively correlated with sediment mud content. Longer, wider leaves, and greater aboveground and belowground biomass were observed at lower salinities, indicating that H. beccarii prefers hyposaline habitats. High shoot density could induce intraspecific competition followed by self-thinning in H. beccarii, leading to reduced leaf area, aboveground and belowground biomass, and root length. Thus, long-term monitoring of seagrass beds along the rapidly urbanizing coastline of Guangdong Province is needed to unravel the mechanisms of decline and to develop effective management strategies.

迅速的城市化导致海草床的加速减少。考察了广东省快速城市化地区整个海岸线上的海草床状况，以记录海草床的变化，并探讨海草特征及其可塑性的决定因素。新发现了13个海草床，总面积为679.04公顷，而已知的11个海草床已从972.55公顷减少到858.67公顷，其中有七个在最近十年中消失了，这主要是由于人工岸线和海滩大坝建设的加剧以及养分的增加鱼笼养和虾塘养殖，牡蛎养殖，红树林种植和贝类采集的投入。椭圆形嗜盐菌的叶氮含量占最大床位的该区域从2011年的（2.09±0.24）％增加到2017年的（3.39±0.18）％，表明富营养化得到增强。百日咳嗜盐菌的最佳海水溶解无机氮和溶解无机磷水平分别为40μmol / L和2.5μmol/ L。Beccarii的立足种群和工厂规模与沉积物泥浆含量呈正相关。更长，更宽的叶子，和更大的地上和地下生物量在较低的盐度观察到，表明H. beccarii喜欢低盐栖息地。高芽密度可以诱导种内竞争，然后在贝卡酵母中自我变薄，导致叶片面积，地上和地下生物量以及根长减少。因此，需要对广东省快速城市化海岸线上的海草床进行长期监测，以揭示下降的机理并制定有效的管理策略。