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.

明晰自上而下与自下而上作用的相对强度，是预测生物群落结构的关键所在。这类作用的强度，部分可通过捕食者种群丰度与养分可获得性进行调控。2009年，我们提出假说：受潮汐格局差异影响，这些因素的重要性在大西洋东南沿岸与墨西哥湾沿岸存在地理分异，并随即采用生物地理学操控性野外实验方法开展该变异规律的研究。尽管我们最初的研究目标是阐明盐沼节肢动物食物网的结构，但墨西哥湾沿岸发生的英国石油公司（BP）深水地平线漏油事件，为我们探究石油泄漏胁迫如何影响实验观测变量提供了契机。此前我们已在墨西哥湾与大西洋沿岸的多个点位布设了样地与样带采样方案，这使得我们能够评估若石油波及部分点位时可能产生的影响。本研究在墨西哥湾沿岸（从德克萨斯州至佛罗里达州）的11个点位，以及大西洋沿岸（从佛罗里达州至缅因州）的11个点位开展。在每个点位，我们对实验样地进行采样，并在紧邻实验样地、高潮沼边界5米范围内布设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，因已知存在石油污染，我们在原有实验点位基础上新增了4个点位，并增设1个对照点位；仅对这些点位开展了样带采样。本数据集包含所有样带采样数据；实验样地的相关数据将在配套数据集中发布。