Description: A 9-month aquarium experiment with the cold-water Dendrophyllia cornigera was conducted to investigate the single and combined effects of warming, acidification and deoxygenation on its ecophysiological response. The experiment took place at the Aquarium finisterrae (A Coruña, Spain) between 2022-05-06 and 2023-02-24. Treatment values for each parameter (current in situ vs. climate change) were: 12 °C and 15 °C (temperature); ~7.99 and 7.69 (pH); ~8.63 mg/L and 6.45 mg/L (dissolved oxygen concentration). A total of eight treatments (with 3 replicates each, 5 L aquaria) were set up. Dry mass of the coral nubbins (3 per experimental aquarium) was assessed by means of the buoyant weight technique (Jokiel et al. 1978, Davies, 1989), using an analytical balance (OHAUS AX124, precision 0.1 mg). The dry mass was calculated considering the nubbin net weight in water, the water density and the skeletal density of D. cornigera (2.63 g/cm3; Movilla et al. 2014). Measurements were performed just once the acclimation time finished and after 2 , 4, 6 and 9 months under the experimental conditions. Skeletal growth rates were calculated as the slope of the linear regression between the logarithmically transformed dry mass and the experimental time (%/day) (Orejas et al. 2011).

Description: Cold-water coral (CWC) reefs constitute one of the most complex deep-sea habitats harboring a vast diversity of associated species. Like other tropical or temperate framework builders, these systems are facing an uncertain future due to several threats, such as global warming and ocean acidification. In the case of Mediterranean CWC communities, the effect may be exacerbated due to the greater capacity of these waters to absorb atmospheric CO2 compared to the global ocean. Calcification in these organisms is an energy-demanding process, and it is expected that energy requirements will be greater as seawater pH and the availability of carbonate ions decrease. Therefore, studies assessing the effect of a pH decrease in skeletal growth, and metabolic balance are critical to fully understand the potential responses of these organisms under a changing scenario. In this context, the present work aims to investigate the medium- to long-term effect of a low pH scenario on calcification and the biochemical composition of two CWCs from the Mediterranean, Dendrophyllia cornigera and Desmophyllum dianthus. After 314 d of exposure to acidified conditions, a significant decrease of 70 % was observed in Desmophyllum dianthus skeletal growth rate, while Dendrophyllia cornigera showed no differences between treatments. Instead, only subtle differences between treatments were observed in the organic matter amount, lipid content, skeletal microdensity, or porosity in both species, although due to the high variability of the results, these differences were not statistically significant. Our results also confirmed a heterogeneous effect of low pH on the skeletal growth rate of the organisms depending on their initial weight, suggesting that those specimens with high calcification rates may be the most susceptible to the negative effects of acidification.

Description: A 9-month aquarium experiment with the cold-water Dendrophyllia cornigera was conducted to investigate the single and combined effects of warming, acidification and deoxygenation on its ecophysiological response. The experiment took place at the Aquarium finisterrae (A Coruña, Spain) between 2022-05-06 and 2023-02-24. Treatment values for each parameter (current in situ vs. climate change) were: 12 °C and 15 °C (temperature); ~7.99 and 7.69 (pH); ~8.63 mg/L and 6.45 mg/L (dissolved oxygen concentration). A total of eight treatments (with 3 replicates each, 5 L aquaria) were set up. Raspberry-based controllers were set to modify and monitor the water temperature, pH and dissolved oxygen in every treatment. Values for temperature (ºC), pH (NBS scale) and oxygen (% air saturation) were registered every 15 minutes in a database. The parameters were measured using PT100 temperature sensors, and Atlas Scientific Lab Grade pH and Dissolved Oxygen sensors. Every set of sensors was placed on each header tank, corresponding to each treatment (8 in total). Parameter setpoint values for each header tank were finely adjusted on the controller to ensure the treatment target values on each experimental aquaria. Oxygen sensors from treatments with ambient oxygen (~8.63 mg/L) were removed from the system due to calibration issues. Here, an example of the results for temperature, pH and oxygen for every header tank over 24 hours on 31st of December 2022 is presented. Values for pH (total scale) and dissolved oxygen (mg/L) were calculated using AquaEnv (Hofmann et al. 2010) and respR (Harianto et al. 2019) R packages, respectively, using the in situ temperature and salinity (35.1).