Detrimental effects of ocean acidification on the economically important Mediterranean red coral (Corallium rubrum)

Abstract

The mean predicted decrease of 0.3-0.4 pH units in the global surface ocean by the end of the century has prompted urgent research to assess the potential effects of ocean acidification on the marine environment, with strong emphasis on calcifying organisms. Among them, the Mediterranean red coral (Corallium rubrum) is expected to be particularly susceptible to acidification effects, due to the elevated solubility of its Mg-calcite skeleton. This, together with the large overexploitation of this species, depicts a bleak future for this organism over the next decades. In this study, we evaluated the effects of low pH on the species from aquaria experiments. Several colonies of C. rubrum were long-term maintained for 314 days in aquaria at two different pH levels (8.10 and 7.81, pHT ). Calcification rate, spicule morphology, major biochemical constituents (protein, carbohydrates and lipids) and fatty acids composition were measured periodically. Exposure to lower pH conditions caused a significant decrease in the skeletal growth rate in comparison with the control treatment. Similarly, the spicule morphology clearly differed between both treatments at the end of the experiment, with aberrant shapes being observed only under the acidified conditions. On the other hand, while total organic matter was significantly higher under low pH conditions, no significant differences were detected between treatments regarding total carbohydrate, lipid, protein and fatty acid composition. However, the lower variability found among samples maintained in acidified conditions relative to controls, suggests a possible effect of pH decrease on the metabolism of the colonies. Our results show, for the first time, evidence of detrimental ocean acidification effects on this valuable and endangered coral species.

Responses of the tropical gorgonian coral Eunicea fusca to ocean acidification conditions

“…This contradicts studies about other MgCO 3 calcifiers (i.e., CCA), which have found significant decreases in calcification with pH levels projected by the end of this century (Agegian 1985;Gao et al 1993;Kuffner et al 2008;Gao and Zheng 2010). However, there are few previous studies experimenting with ocean acidification on octocorals; one study focused on three species of tropical soft corals from the Red Sea (Gabay et al 2013) and another one on temperate octocorals from the Mediterranean Sea (Bramanti et al 2013).…”

“…Although the information is scarce, there are a few studies that have addressed this question (Bramanti et al 2013;Gabay et al 2013Gabay et al , 2014. Bramanti et al (2013) evaluated the long-term effects of low pH in the Mediterranean red coral Corallium rubrum, grown under two different pH conditions and found a detrimental effect of pH on calcification rates and sclerite morphology.…”

“…Although the information is scarce, there are a few studies that have addressed this question (Bramanti et al 2013;Gabay et al 2013Gabay et al , 2014. Bramanti et al (2013) evaluated the long-term effects of low pH in the Mediterranean red coral Corallium rubrum, grown under two different pH conditions and found a detrimental effect of pH on calcification rates and sclerite morphology. On the other hand, Gabay et al (2013), working on three different species of soft corals, demonstrated no deleterious effects of ocean acidification on protein concentration, polyp weight, density of zooxanthellae, chlorophyll concentration and polyp pulsation rate.…”

Resistance of Two Mediterranean Cold-Water Coral Species to Low-pH Conditions

“…At the beginning of the experiment, 24 nubbins of L. pertusa (2-5 polyps) and 36 of M. oculata (8-20 polyps) were selected and randomly distributed and incubated together into six 30 litres aquaria subject to two pH treatments (8.10 and 7.81 for control and acidified conditions, respectively; 3 replicates per treatment). See Bramanti et al [24] for further details on the experimental setup. Discrete analyses of total alkalinity (TA) by potentiometric titration [25,26] and seawater pH by spectrophotometry [27] were carried out periodically.…”

Comparison of the alkalinity and calcium anomaly techniques to estimate rates of net calcification

“…It is nondestructive and offers the possibility of studying the same organism and following its calcification over time (e.g. Martin & Gattuso 2009, Bramanti et al 2013, Gazeau et al 2014). Another option is to estimate the linear extension (growth) of an organism, assuming the density of its calcifying structures is known.…”