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.