Comparative transect surveys of invertebrate abundance, plant cover, and sediment characteristics in Atlantic and Gulf of Mexico salt marshes from April 2009 to September 2010

Understanding the relative strengths of top-down and bottom-up forces is an important key to predicting the structure of biological communities. The strength of these effects can be regulated in part by predator abundance and nutrient availability. In 2009, we hypothesized that the importance of these factors varies geographically between the southeastern Atlantic Coast and the Gulf Coast due to differences in tidal regime, and began to study this variation using a biogeographic, manipulative field experiment. Although our original purpose was to understand the structure of salt marsh arthropod food webs, BP's Deepwater Horizon spill in the Gulf Coast presented an opportunity to understand how stress from an oil spill might affect the variables that we were measuring. The fact that we had plots and transect sampling in place at multiple sites along the Gulf and East Coasts put us in a position to evaluate any impacts that might occur if oil hit some of the sites. The study was conducted at 11 sites across the Gulf Coast, from Texas to Florida, and 11 sites along the Atlantic Coast, from Florida to Maine. At each site, experimental plots were sampled and a 100m transect was sampled near the plots within 5m of the high marsh boundary. Sampling was conducted in May 2009, August 2009, and August 2010. In 2010, four extra sites were added to the existing experimental sites because of known oil contamination, and another site was added as an extra control. Only the transect sampling was conducted at these sites. This dataset contains all the transect data; data from experimental plots will be reported in a companion dataset.厘清下行调控力（top-down force）与上行调控力（bottom-up force）的相对强弱，是预测生物群落结构的关键所在。这类调控效应的强弱，在一定程度上受捕食者丰度与养分可获得性的调控。2009年，我们提出假说：受潮汐格局（tidal regime）差异的影响，这些调控因子的重要性在大西洋东南沿岸与墨西哥湾沿岸（Gulf Coast）存在地理分异，并随即开展了生物地理学视角下的操控性野外实验（biogeographic manipulative field experiment）以探究该分异规律。尽管本研究最初旨在阐明盐沼节肢动物食物网（salt marsh arthropod food webs）的结构，但英国石油公司（BP）深水地平线（Deepwater Horizon）油井泄漏事件在墨西哥湾沿岸的发生，为我们探究石油泄漏带来的胁迫如何影响实验观测变量提供了契机。我们已在墨西哥湾沿岸与大西洋沿岸（Atlantic Coast）的多个样点布设了实验样方（experimental plots）与样带采样（transect sampling）方案，这使得我们能够评估石油污染波及部分样点后可能产生的影响。本研究的野外工作覆盖墨西哥湾沿岸从得克萨斯州至佛罗里达州的11个样点，以及大西洋沿岸从佛罗里达州至缅因州的11个样点。在每个样点中，我们对实验样方进行采样，并在距离高潮沼（high marsh）边界5米范围内的样方附近布设100米样带开展采样。采样工作分别于2009年5月、2009年8月及2010年8月开展。2010年，鉴于已确认的石油污染情况，我们在原有实验样点基础上新增了4个受污染样点，并增设1个对照样点；此类新增样点仅开展了样带采样。本数据集包含所有样带采样数据；实验样方的采样数据将在配套数据集中发布。