The effects of oiling on salt marsh and mangrove macrofauna communities at the Chandeleur Islands, LA (June and September 2016)

To determine the relative abundances, species number, and composition of macrofauna, all plots were sampled at high tide during the growing season (June and September) in 2016 in the Chandeleur Islands, LA. At each sampling location, water depth was measured and density differences between marsh plants (Spartina shoots) and black mangrove pneumatophores were also quantified. Macrofauna were collected within 1 m of the plant/water interface, which is the area known to harbor high organism abundances in salt marsh systems. We haphazardly tossed three 0.17 m^2 plastic cylinders in each plot, whose lower edge was embedded in the sediment. The contents of the cylinders were collected using a gasoline-powered suction pump and all material was retained in a 0.5 mm mesh collection bag. Following collection, samples were removed from the bag and rinsed over a 0.5 mm sieve to remove any extraneous material, then were placed on ice and frozen. Animals were later identified to the lowest practical taxonomic level. Portunid crabs and penaeid shrimp were measured for total length. Biomass (DW = dry weight, ± 0.0001 g) was determined by drying organisms at 70°C to a constant weight. Samples were then muffled at 500°C to obtain ash weight (AW, ± 0.0001 g). Ash-free dry weight was calculated as DW-AW. Samples were placed in a desiccator to cool before any weights were recorded.