Here, we report the results of a multiple stressor experiment combining impacts of ocean acidification and Polymetallic sulfide (PMS) deposits produced by deep-sea mining on larval survival of the deep-sea coral Desmophyllum pertusum (syn. Lophelia pertusa). Adult colonies of D. pertusum were collected in December and January 2022 at Tisler reef, at depths between 100-120 m. Adults were maintained in aquaria and after spawning, embryos were collected and left to develop to 7-day larvae. On day 7, larvae were exposed to four experimental treatments and their combinations: two pCO2 treatments recreating present conditions (400 ppm), and conditions projected to the end of the century (RCP8.5, 1000 ppm), as well as two mining treatments corresponding to PMS particles (concentration 5 mg/L), and their leachates. Survival was monitored every 24h.

Experimental treatment: CTR: present pCO2, no mining; AC: end of century pCO2, no mining; CTR-SED: present pCO2 and PMS sediment; CTR-MET: present pCO2 and PMS leachates; AC-SED: end-of-century pCO2 and PMS sediment; AC-MET: end-of-century pCO2 and PMS leachatesCTR/present: pcO2 400 ppm; Low/end-of-century: pCO2 1000 ppmNo: No mining sediment; Sediment: sediment, metals only: metal leachates without sediment