Gaurisas, Daniela Y; de Jonge, Danielle; Bernardino, Angelo Fraga; Sweetman, Andrew K: Macrofauna from stable isotope tracer incubation experiments under climate change projections in the Cabo Verde Basin, NE Atlantic [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.977643 (dataset in review)

An experimental approach was developed to assess the individual and combined effects of two climate change stressors (temperature and POC quality) on benthic macrofaunal assemblages in the bathyal continental slope of the Cabo Verde Basin (CVB, Equatorial Atlantic). The study used stable isotope tracer incubation experiments with 13C and 15N labelled diatoms Phaeodactylum tricornutum, to simulate climate change projections for the next century. A balanced experimental design was employed to examine the impacts of increased temperature (+2 °C), reduced POC quality (dialysed labile fraction), or both, compared to a control treatment. The experiments were carried out onboard the research vessel Sarmiento de Gamboa during the iMirabilis2 campaign in August 2021 (Orejas et al., 2022). A total of 19 sediment samples were collected by four multi-corer (MUC) deployments. From each MUC deployment, four cores with clear overlying water were randomly selected and assigned among the four different treatments (total n= 4 for each of 4 treatments), and the remaining three cores were used as background for natural stable isotopes. The upper 15-18 cm of sediment from each core was extruded to an incubation core (inner diameter 10 cm) closed airtight at the bottom. The incubation cores were placed in buckets with filtered seawater at the experimental temperature. After an equilibration period of 147 to 173 hours, the stable isotope experiment began with the injection of 12.5 mg of fresh or partially degraded diatoms into each core, representing approximately 10% of the average annual POC flux for the region (Sweetman et al., 2017). The experiment lasted 48 hours after the algae injection, with the cores maintained under constant aeration. At the experiment's conclusion, sediment samples were fixed in 10% borax-buffered formalin seawater. In the laboratory, the samples were washed, sieved through a 300 µm mesh, and preserved in ethanol until analysis. Macrofaunal organisms were sorted, taxonomically identified, and assessed for density and biomass. Samples were dried at 45°C to achieve a stable mass, with calcareous organisms being acidified before a second drying. The dried samples were then analyzed for dry mass, carbon and nitrogen content, and stable isotope values (δ13C, δ15N). Carbon and nitrogen incorporation rates were subsequently calculated based on the stable isotope values.