RAPID: Degradation and Resilience of Seagrass Ecosystem Structure and Function following a Direct Impact by Hurricane Harvey

长期以来，干扰一直被认为是海洋生物群落中的一种主要组织力量，有可能塑造生物多样性。飓风提供了一个自然实验，以了解剧烈的物理扰动(风暴潮和风能)如何与环境条件(盐度或浊度)的长期变化相互作用，以改变生态群落的结构和功能。由于模型表明，飓风强度和降雨量将随着气候变暖而增加，因此了解沿海生态系统的反应和恢复具有至关重要的社会意义。2017年8月25日，哈维以4级飓风的身份在德克萨斯州海岸登陆，随着风暴在德克萨斯州中部海岸停滞，哈维带来了极端降雨。暴雨和淡水径流造成了低盐度透镜，并在两个月后继续存在。海草生态系统可能特别脆弱，因为它们生长在浅的软沉积物海底(因此很容易被移位或掩埋)，而且海草对盐度和浊度的变化很敏感。海草损失的社会影响是公认的：海草为河口和近岸依赖渔业提供极有价值的生态系统服务，具有很大的经济价值，作为苗圃栖息地，并在全球范围内封存数十亿吨碳。通过测量海草及其栖息地社区的健康和功能，私人投资者正在评估飓风和持续淡水透镜的影响。通过观察未受影响的地点和之前六年的数据，提供了背景。该项目解决了主要问题：强烈的物理干扰加上长期的化学物理扰动如何影响海草群落结构和功能的损失和恢复，包括当地生产、营养联系和后生动物群落多样性？为了了解飓风哈维对得克萨斯州中部海岸海草生态系统的影响，研究人员正在(1)记录物理栖息地结构的损失，(2)梳理与风暴事件相关的多种应激源对生物多样性和生态系统功能的独立和交互影响，以及(3)确定促进干扰后恢复能力的因素。一个全州范围的海草监测计划，包括哈维路径和周围海草系统内地区六年的数据，将提供宝贵的背景信息。调查人员正在测量海草结构，在经历过严重物理损害和适当参考地点的地点采用事前-事后控制-撞击设计。风暴后部署的现场记录仪跟踪低盐度事件的演变以及海草的生理应激测量(例如，叶绿素荧光、色素损失、生长减少)。海草栖息地功能的变化是通过测量通过岩芯、底栖推网和围网采样的受影响和参考地点内的动物多样性来评估的。对海草叶片和常见无脊椎动物猎物进行系链分析，可以比较不同干扰影响的地点之间的营养相互作用。这些数据被用来创建生态系统对极端干扰事件的反应模型，并确定最能预测栖息地物理结构和相关生态系统功能恢复的因素。

Disturbance has long been recognized as a major organizing force in marine communities with the potential to shape biodiversity. Hurricanes provide a natural experiment to understand how acute physical disturbances (storm surge and wind energy) may interact with longer-term changes in environmental conditions (salinity or turbidity) to alter the structure and function of ecological communities. As models indicate that hurricane intensity and precipitation will increase with a warming climate, understanding the response and recovery of coastal ecosystems is of critical societal importance. Harvey made landfall as a Category Four hurricane on the Texas coast on August 25, 2017, bringing extreme rainfall as the storm stalled over the middle Texas coast. The heavy rainfall and freshwater run-off created a low salinity lens that continues to persist two months later. Seagrass ecosystems may be particularly vulnerable because they grow on shallow, soft-sediment bottoms (and thus are easily dislodged or buried) and because seagrasses are sensitive to changes in salinity and turbidity. The societal implications of seagrass loss are well recognized: seagrasses provide highly valuable ecosystem services of large economic value for estuarine and nearshore dependent fisheries, serve as nursery habitats, and sequester gigatons of carbon on a global scale. Using measurements of the health and function of the seagrass and of the community for which it is habitat, the PIs are assessing the impact of the hurricane and of the persistent freshwater lens. Context is provided by looking at non-impacted sites and by six prior years of data.This project addresses the overarching question: How do intense physical disturbances in conjunction with chronic chemophysical perturbations affect loss and recovery of seagrass community structure and function, including local production, trophic linkages, and metazoan community diversity? To understand the impacts of Hurricane Harvey on seagrass ecosystems across the middle Texas coast, the investigators are (1) documenting losses in physical habitat structure, (2) teasing apart independent and interactive effects of multiple stressors associated with storm events on biodiversity and ecosystem function, and (3) identifying factors that promote resilience following disturbance. A state-wide seagrass monitoring program with six years of data from areas within Harvey's path and surrounding seagrass systems will provide invaluable context. The investigators are measuring seagrass structure, employing a Before-After-Control-Impact design at sites that experienced severe physical damage and appropriate reference sites. In situ loggers deployed after the storm track the evolution of the low salinity event together with seagrass physiological stress measurements (e.g. chlorophyll fluorescence, pigment loss, reduced growth). Changes in seagrass habitat function is assessed through measurements of faunal biodiversity within impacted and reference sites sampled via cores, benthic push nets, and seine nets. Tethering assays of seagrass blades and common invertebrate prey enables comparison trophic interactions across sites that vary in disturbance impact. These data are used to create models of ecosystem response to an extreme disturbance event and identify factors that best predict recovery of the physical structure of the habitat and of associated ecosystem functions.