Abstract
Rising temperatures and ocean acidification driven by anthropogenic carbon emissions threaten both tropical and temperate corals. However, the synergistic effect of these stressors on coral physiology is still poorly understood, in particular for cold-water corals. This study assessed changes in key physiological parameters (calcification, respiration and ammonium excretion) of the widespread cold-water coral Desmophyllum dianthus maintained for ∼8 months at two temperatures (ambient 12 °C and elevated 15 °C) and two pCO2 conditions (ambient 390 ppm and elevated 750 ppm). At ambient temperatures no change in instantaneous calcification, respiration or ammonium excretion rates was observed at either pCO2 levels. Conversely, elevated temperature (15 °C) significantly reduced calcification rates, and combined elevated temperature and pCO2 significantly reduced respiration rates. Changes in the ratio of respired oxygen to excreted nitrogen (O:N), which provides information on the main sources of energy being metabolized, indicated a shift from mixed use of protein and carbohydrate/lipid as metabolic substrates under control conditions, to less efficient protein-dominated catabolism under both stressors. Overall, this study shows that the physiology of D. dianthus is more sensitive to thermal than pCO2 stress, and that the predicted combination of rising temperatures and ocean acidification in the coming decades may severely impact this cold-water coral species.
Highlights
Increases in anthropogenic carbon emissions, leading to rising sea temperatures and ocean acidification, have resulted in extensive tropical coral bleaching (e.g., HoeghGuldberg, 1999; Mcleod et al, 2013) and decreased coral calcification rates (e.g., Gattuso et al, 1998; Chan & Connolly, 2012; Movilla et al, 2012; Bramanti et al, 2013)
The results of this study show that the cold-water corals (CWC) D. dianthus is more sensitive to changes in temperature than to ocean acidification stress
This CWC maintains its metabolism under elevated pCO2, whereas calcification is significantly reduced under elevated temperatures
Summary
Increases in anthropogenic carbon emissions, leading to rising sea temperatures and ocean acidification, have resulted in extensive tropical coral bleaching (e.g., HoeghGuldberg, 1999; Mcleod et al, 2013) and decreased coral calcification rates (e.g., Gattuso et al, 1998; Chan & Connolly, 2012; Movilla et al, 2012; Bramanti et al, 2013). While considerable research efforts have focused on tropical and temperate corals, less is known about the effects of ocean warming and acidification on cold-water corals (CWC) (e.g., Guinotte et al, 2006; Rodolfo-Metalpa et al, 2015 and references therein). These corals are among the most important ecosystem engineering species (sensu Jones, Lawton & Shachak, 1994) in the deep sea, where they build three-dimensional frameworks (Roberts, Wheeler & Freiwald 2006) that support a highly diverse associated fauna (Henry & Roberts, 2007; Buhl-Mortensen et al, 2010). Elevated seawater temperatures increased calcification in the nonreef forming Dendrophyllia cornigera (Naumann, Orejas & Ferrier-Pagès, 2013; Gori et al, 2014a); had no effect on calcification in the solitary coral Desmophyllum dianthus (Naumann, Orejas & Ferrier-Pagès, 2013); and had either no effect on the reef-forming Lophelia pertusa calcification (Hennige et al, 2015) or induced mortality (Brooke et al, 2013) depending upon the site of origin and change in temperature
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