The aim of this study was to determine the impact of crude oil contamination on sponge Halichondria panicea. Therefore H. panicea samples were exposed to control seawater, water accomodated oil fraction, chemically enhanced water accomodated oil fraction, DMSO or Benzo-A-Pyrene in seawater solutions for 48 hours. Experiment design:The experimental apparatus used in this study, was constituted of 12 individual glass incubation chambers of 750 mL of volume, sealed with a polytetrafluoroethylene lid. Each chamber was equipped with a magnetic stirrer at the top of the chamber. An inflow and outflow in the lid allowed seawater to flow through the chamber at a rate of 750 mL/day, thanks to multichannel peristaltic pumps (figure S1). PTFE tubing connected the chambers to the peristaltic pumps to limit to a maximum the use of plastic (which would interact with hydrocarbons). One individual sponge sample was placed in each incubation chamber at the beginning of the experiments. All experiments were conducted in the dark to avoid photo oxidation and in a temperature controlled room (10° C). Treatment solution preparation:Schiehallion crude oil (BP) and dispersant Slickgone NS (Dasic International) were used in this study. Schiehallon crude oil is produced at Schiehallion oil field in the Faroe-Shetland channel. The crude oil is characterised by an American Petroleum Institute gravity of 25.2, a sulphur content of 0.46 % and a viscosity of 67 centistokes (cST) at 20° C (BP, 2017). Slickgone NS is one of the dispersants approved for use by the United-Kingdom Marine Management Organisation and is listed for potential use in the Faroe-Shetland channel in the case of a spill (BP, 2014 Marine Management Organisation, 2018). To prepare WAF and CEWAF solutions, we followed the standard protocol developed by the Chemical Response to Oil Spills: Ecological Research Forum (Aurand and Coelho, 2005). Weighed amounts of Schiehallion crude oil was added to 1 L seawater solutions and mixed for 18 h at a speed of 180 rpm for the WAF solutions (to avoid the formation of a vortex) and at a speed of 300 rpm for the CEWAF solutions (to allow the formation of a small vortex) as suggested by Aurand and Coelho (2005) . For CEWAF solutions, dispersant Slickgone NS (Dasic International) was applied at a volume ratio of 1:10 as advised by the manufacturers. At the end of the mixing time, solutions were left to settle for 3 h and the water fraction was carefully removed and placed into a clean 1 L Duran bottle. To produce a solution of BaP in seawater at a final concentration of 10 µg/L, BaP was first dissolved in dimethyl sulfoxide (DMSO) before being added to the seawater (final dilution 0.01% v/v). To exclude any effect of the DMSO in the BaP treatment, a DMSO treatment (0.01% v/v) was also added. For the BaP solution, a stock solution of BaP in DMSO at a concentration of 0.1 g/L was first prepared. 100 µL of stock solution was then added to 999.9 mL of artificial seawater prior to the use in the experiment. The same volume of DMSO was also added to artificial seawater in the DMSO solution.RNA extraction and sequencing:Total RNA was extracted from tissue samples collected at the end of the exposure in all experiments. Total RNA was extracted from sponge tissue samples using Qiagen Total RNA Blood and Tissue Extraction kits following the manufacturer’s protocols. DNA was removed from the RNA extractions with Qiagen DNase sets. At the end of the protocol, RNA was eluded into 30 µL of DNA/RNA free sterile water. RNA quality and quantity were then assessed by spectrophotometer using a NanoDrop.RNA extraction from all twelve samples of the single exposure experiment were sent to Edinburgh Genomics for Illumina TruSeq stranded Poly-A selected mRNA-seq library preparation and Illumina HiSeq 4000 RNA-sequencing. Paired-end reads were run to 75 bp to yield at least 290 M + 290 M reads.