Respiration of Mediterranean cold-water corals is not affected by ocean acidification as projected for the end of the century

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 <i>Madrepora oculata</i> and <i>Lophelia pertusa</i> 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 <i>p</i>CO₂ affected the energetic requirements of these corals. Over the course of three months, rates of respiration were measured at a <i>p</i>CO₂ 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 <i>L. pertusa</i> and <i>M. oculata</i>, respectively, and were independent of <i>p</i>CO₂. 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 <i>p</i>CO₂ is a general feature of deep-sea corals in other regions

Interactive Effects of Ocean Acidification and Warming on Growth, Fitness and Survival of the Cold-Water Coral Lophelia pertusa under Different Food Availabilities

“…It would therefore be worthwhile to measure the metabolic rate of the corals under long-term influence of ocean acidification and warming in order to see if the increased costs of mineralisation are reflecting in enhanced respiration for instance. In two mid-and longterm studies, respiration rates did not significantly change with elevated pCO 2 levels compared to ambient levels (Maier et al, 2013b;Hennige et al, 2015), while a significant decline was found after short-term exposure to acidified conditions (3 weeks at 750 µatm) (Hennige et al, 2014). Elevated temperature by 2 • C led to a 50% increase in respiration rates of L. pertusa (Dodds et al, 2007), but combined long-term exposure of elevated temperature and CO 2 concentration did not result in significant changes (Hennige et al, 2015).…”

“…We aimed at identifying how differently L. pertusa reacts towards multiple climate change stressors when fed with a higher amount of zooplankton food compared to 10-fold lower food availability. It was suggested that calcification rates might be maintained under an acidified environment via mobilising lipid reserves from the coral's tissue (Maier et al, 2013b;Hennige et al, 2014), but this source of stored energy is bound to decline on longer time scales. Furthermore, elevated temperatures might lead to increased metabolic rates (Dodds et al, 2007) that require additional energetic input.…”

Fine-scale nutrient and carbonate system dynamics around cold-water coral reefs in the northeast Atlantic

“…The natural fluctuations in the physicochemical conditions (including oxygen, carbon, nutrients and food supply), driven by large hydrodynamics, may provide flexibility for these organisms, giving them increased adaptation potential for surviving a range of conditions, as has been found with warm-water corals and temperature34. This naturally fluctuating environment could help to explain the high levels of variability found in CWCs ocean acidification experiments, especially as several recent laboratory experiments CWCs are able to continue calcifying under high CO 2 , low Ω Aragonite conditions [e.g 353637…”

Biogeographic variability in the physiological response of the cold‐water coral Lophelia pertusa to ocean acidification

“…Recent experimental work has revealed considerable variation in the physiological response of cold‐water corals to ocean acidification (Maier et al . , , ,b; Form & Riebesell ; Hennige et al . ; Lunden et al .…”

“…In contrast, a recent 3‐month study on both L. pertusa and M. oculata found no significant change in either respiration or calcification rates even with CO 2 concentrations as high as 1000 ppm (pH of approximately 7.73; Maier et al . ,b). Calcification, skeletal density and energy reserves in Dendrophyllia cornigera did not change significantly during a 314‐day acidification experiment with pH values as low as 7.81; however, in the same study, Desmophyllim dianthus exhibited a significant, 70% reduction in calcification (Movilla et al .…”