Abstract
Abstract. The rise of CO2 has been identified as a major threat to life in the ocean. About one-third of the anthropogenic CO2 produced in the last 200 yr has been taken up by the ocean, leading to ocean acidification. Surface seawater pH is projected to decrease by about 0.4 units between the pre-industrial revolution and 2100. The branching cold-water corals Madrepora oculata and Lophelia pertusa are important, habitat-forming species in the deep Mediterranean Sea. Although previous research has investigated the abundance and distribution of these species, little is known regarding their ecophysiology and potential responses to global environmental change. A previous study indicated that the rate of calcification of these two species remained constant up to 1000 μatm CO2, a value that is at the upper end of changes projected to occur by 2100. We examined whether the ability to maintain calcification rates in the face of rising pCO2 affected the energetic requirements of these corals. Over the course of three months, rates of respiration were measured at a pCO2 ranging between 350 and 1100 μatm to distinguish between short-term response and longer-term acclimation. Respiration rates ranged from 0.074 to 0.266 μmol O2 (g skeletal dry weight)−1 h−1 and 0.095 to 0.725 μmol O2 (g skeletal dry weight)−1 h−1 for L. pertusa and M. oculata, respectively, and were independent of pCO2. Respiration increased with time likely due to regular feeding, which may have provided an increased energy supply to sustain coral metabolism. Future studies are needed to confirm whether the insensitivity of respiration to increasing pCO2 is a general feature of deep-sea corals in other regions.
Highlights
Y (38 to 39) (Freiwald et al, 2009; Tursi et al, 2004)
For the comparison of carbonate chemistry among the four pressure of CO2 (pCO2) treatments (A–D) of bulk seawater prepared at T1–T4, a one-way ANOVA was conducted followed by a Tukey HSD post hoc comparison
The pCO2 of bulk seawater prior to the incubations differed from the pCO2 levels that were adjusted by aeration using pre-mixed air–CO2 for treatment A (280 ppm), B (400 ppm), C (700 ppm) and D (1000 ppm)
Summary
Colonies of the cold-water corals M. oculata and L. pertusa were collected during the MedSeaCan cruise in June 2009 in the Lacaze-Duthiers canyon at water depths of 260 m (42◦35.07 N, 03◦24.14 E), 267 m (42◦34.98 N, 03◦24.15 E) and 500 m (42◦32.98 N, 03◦25.21 E), using a remotely operated vehicle. Corals were transported to the laboratory and maintained in a temperature-controlled room until the start of the experiments. Surface water with a salinity of 38 was pumped into two 110 L storage tanks and maintained at 11 ◦C in the temperature-controlled room. Water was delivered to maintenance vials at a flow rate of 32 ± 14 mL h−1. The vials were maintained in four water baths and temperature was adjusted to 13 ± 0.1 ◦C using electronic temperature controllers (Corema) coupled with aquarium heaters (Tetratec HT75). The seawater of the water baths containing the maintenance vials was adjusted to the intended pCO2 by bubbling with an air stone (HOBBY ceramic air diffuser, 150 mm in length). MO 16 28.9 8.3 2.0 1.3 0.446 0.453 0.148 0.076 the 3-month duration of the experiment except during incubations aimed at determining rates of respiration ( section) or calcification (Maier et al, 2013)
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