Resource managers rely on large‐scale flow and habitat enhancement actions to support sensitive species in the San Francisco Bay–Delta. The effects of these actions on target species and ecosystems are largely unknown. In 2018, we implemented an ecosystem‐scale experiment to reduce salinity and improve access to high‐quality habitat in Suisun Marsh, California, for Endangered Species Act‐listed Delta Smelt Hypomesus transpacificus. The action included a release of approximately 46 million m³ of additional flow in conjunction with the operation of a novel water management facility, the Suisun Marsh Salinity Control Gates. This experimental action resulted in more low‐salinity habitat in Suisun Marsh than would have been present as compared to similar historical low‐flow summer conditions. We evaluated the effect of decreasing salinity on the species assemblage in Suisun Marsh using a combination of ordination analyses and circular statistics. We focused this analysis on long‐term monitoring data collected within Suisun Marsh during July and August and found that the aquatic community changed significantly in small sloughs but not large‐slough habitat in response to the Suisun Marsh action. The assemblage shift from July to August 2018 differed from historical trends in both slough sizes, albeit not significantly in large‐slough habitat. Specifically, we observed (1) a shift in California bay shrimp Crangon franciscorum and Striped Bass Morone saxatilis abundance like that occurring in low‐salinity, wet water year types; and (2) an uncharacteristic seasonal decline in Black Sea jellyfish Maeotias marginata. We posit that the observed community changes were driven by a combination of behavioral responses to lower‐salinity conditions and physical displacement by directional flow resulting from the flow management action.

中文翻译：

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大规模流量管理行动推动河口生态响应

资源管理者依靠大规模的流量和栖息地改善行动来支持旧金山湾三角洲的敏感物种。这些行动对目标物种和生态系统的影响在很大程度上尚不清楚。2018年，我们针对濒临灭绝物种法案列出的Delta Smelt Hypomesus transpacificus实施了生态系统规模的试验，以减少盐分并改善加利福尼亚州Suisun Marsh的高质量栖息地。行动包括释放约4600万立方米³新型水管理设施Suisun Marsh盐度控制闸的运行带来的额外流量。与类似的历史低流量夏季条件相比，该实验活动导致了遂孙沼泽的低盐度生境比以前更多。我们使用排序分析和循环统计相结合的方法，评估了盐度降低对遂孙沼泽湿地物种聚集的影响。我们将此分析集中于7月和8月Suisun沼泽内收集的长期监测数据，发现响应Suisun Marsh行动，水生生物群落在小泥沼中发生了显着变化，但在大泥沼栖息地中却没有显着变化。从2018年7月到2018年8月的组合变化与两个泥沼尺寸的历史趋势不同，尽管在大泥沼栖息地中并不明显。具体来说，我们观察到（1）加利福尼亚湾虾的迁移象低盐度，湿水年类型中的那样，有橘子兰和条纹鲈Morx丰富。（2）黑海水母Maeotias marginata的季节性下降。我们假设观察到的群落变化是由对低盐度条件的行为响应和流动管理行为导致的定向流动引起的物理位移的综合作用所驱动的。