Seagrasses influence local hydrodynamics by inducing drag on the flow and dampening near-bed velocities and wave energy. When seagrasses are lost, near-bed currents and wave energy can increase, which enhances bottom shear stresses, destabilizes sediment, and promotes suspension and erosion. Though seagrasses are being lost rapidly globally, the magnitude of change in sediment stabilization following ecosystem-wide eelgrass loss has rarely been measured. In this study, we explored the geomorphological changes associated with an unprecedented estuary-wide collapse of a seagrass (eelgrass, Zostera marina) in Morro Bay, CA, USA. Morro Bay has historically suffered from accelerated sedimentation and accretion. However, following massive eelgrass loss since 2010, over 90% of locations that previously had eelgrass experienced erosion. Elevation losses (erosion) reached 0.50 m in some places (mean loss of 0.10 m) with as much as a 50% decrease (median decrease of 13.6%) in elevation (i.e., increase in depth) compared to pre-decline levels. In comparison, the mouth of the estuary, where eelgrass was largely retained, had only 27.7% of the locations with prior eelgrass experiencing erosion and underwent a mean elevation increase (accretion) of 0.32 m. Thus, the loss of eelgrass appears to have altered dynamics at the seabed and transitioned large regions of the estuary from an environment that promotes deposition and accretion to one that promotes suspension and erosion. Large-scale erosion following seagrass loss may be predictive of future shoreline and coastal habitat changes and is likely to be exacerbated by increased storm surge and sea level rise expected with climate change.

海草通过在水流上产生阻力并抑制近地层速度和波浪能来影响局部水动力。当海草丢失时，近床海流和波浪能会增加，这会增加底部切应力，使沉积物不稳定并促进悬浮和侵蚀。尽管海草正在全球范围内迅速流失，但很少测量整个生态系统范围内的海草损失后沉积物稳定变化的幅度。在这项研究中，我们探讨了与海草前所未有的河口范围塌陷有关的地貌变化（鳗草，Zostera码头）在美国加利福尼亚州莫罗湾。莫罗贝（Morro Bay）历来遭受沉淀和积聚的加速。但是，自2010年以来鳗鱼草大量流失后，先前有鳗草草的地点中有90％以上遭受侵蚀。与下降前的水平相比，某些地方的高程损失（侵蚀）达到0.50 m（平均损失0.10 m），而海拔高度（即深度的增加）降低了50％（中值降低了13.6％）。相比之下，鳗鱼在很大程度上保留的河口口中，只有27.7％的先前鳗鱼遭受侵蚀，平均海拔升高（增生）为0.32 m。从而，鳗草的损失似乎已改变了海床的动力，并使河口的大部分区域从促进沉积和增加的环境过渡到了促进悬浮和侵蚀的环境。海草损失后的大规模侵蚀可能预示着未来的海岸线和沿海生境变化，并且风暴潮的增加和气候变化带来的海平面上升可能会加剧这种侵蚀。