Growth rates of the cold-water coral Desmophyllum dianthus during an ex-situ experiment in the Azores

We conducted a medium-term (4 months) multiple stressor experiment with the cold-water coral Desmophyllum dianthus under future environmental conditions (IPCC RCP 8.5 scenarios for 2100), and sediment plumes generated during the potential extraction of seafloor massive sulphides. The experiment followed a two-step approach, where during the first 3 months, corals were exposed to four different treatments combining predicted scenarios of ocean acidification (pCO2/pH) and food availability. Two levels of pCO2 conditions were considered: natural habitat present day conditions (~500 µatm, 720 m depth) and IPCC RCP8.5 scenario (1000 µatm; IPCC, 2019), corresponding to pHT values of 7.93 and 7.66, respectively. In addition, two food availability regimes were recreated: high frequency of feeding (food delivered twice a day / 7 days a week) and low frequency of feeding (food delivered every other day). There were six replicate 13 L aquaria per treatment (4 D. dianthus per aquaria) at a temperature of 10.5 ± 0.1 ºC. During the fourth month of the experiment, suspended polymetallic sulphide particles generated during potential mining activities were added to half of the aquaria under the climate change scenarios at a concentration of 10 mg/l, making 8 treatments in a fully crossed experimental design for the 3 factors tested (OA, food, mining particles). Growth rates were measured using the buoyant weighing technique (Jokiel et al. 1978), using a balance (Mettler-Toledo ME204T) with a precision of 0.1 mg. Corals were weighed twice during the experiment: 1-2 weeks after the start of the experiment and just before the second phase of the experiment with PMS addition, which corresponded to a time interval of 63-71 days.