Dataset: Infaunal community composition and sediment grain size distribution, porosity, and organic content of sediment cores collected in the Northern Gulf of Mexico off the Alabama (USA) coast during 2020 and 2021 before and after Hurricane Sally

Sediment coring was carried out from the R/V E.O. Wilson, operated by Dauphin Island Sea Lab. Sediment cores (9.6-centimeters (cm) inner diameter) were collected with an Ocean Instruments MC-400 multicorer or via SCUBA diving at each site and timepoint. Four replicate cores were sieved (500 micrometers (μm) mesh) and retained contents were preserved in 95% ethanol with Rose Bengal tissue stain (0.05 grams per liter (g L-1)). Stained infauna were identified to family level and enumerated. Taxa that could not be reliably identified to family level were grouped into higher levels of classification (e.g., Nemertea). Infauna were also divided into size classes of body thicknesses of <1 millimeter (mm) and >1 mm. Body length and biomass could not be determined for a large number of specimens, especially annelids (the most abundant phylum), due to fragmentation during collection and preservation (only annelids with intact heads were counted). Body width was measured under a dissecting microscope with a ruler. Grain size was measured in the top 8-12 cm of sediment. 1-2 cores were sectioned into 1 cm increments and dried at 65 degrees Celsius (°C) for 48 hours. Dried samples were placed in a muffle furnace at 550 °C for 4 hours to combust sediment organic matter. Porosity and organic content were calculated from the sediment mass differences before and after drying and combusting, respectively. Combusted sediment was then placed in a 1% sodium hexametaphosphate solution for at least 3 weeks to deflocculate. After weeks of deflocculating, clumps of mud often remained intact in muddier samples, so all samples were gently rubbed with a gloved finger on a 63 μm sieve to break up mud clumps. The mud was then washed through the sieve and combined with the sand retained on the sieve. After breaking up clumps, we measured grain size distribution using a Malvern Mastersizer 3000. For each sample, 5 measurements were averaged and then analyzed using Gradistat (Kenneth Pye Associates, LTD.). Bottom water salinity and temperature (°C) were measured at each site and timepoint using a Seabird SBE 25 Sealogger CTD (conductivity, temperature, depth) instrument array. The CTD was deployed on a line by a winch that lowered the CTD to the bottom and then brought it back to the surface at each site.