Effect of Elevated Carbon Dioxide on Two Scleractinian Corals:Porites cylindrica(Dana, 1846) andGalaxea fascicularis(Linnaeus, 1767)

Abstract

This study reveals the effect of elevated pCO 2 on Porites cylindrica and Galaxea fascicularis. The corals responded differently under elevated pCO 2 . Zooxanthellae cell density, cell mitotic index, and photosynthesis rate of P. cylindrica decreased drastically under the elevated pCO 2 . At the end of the experiment, P. cylindrica suffered from a declining calcium carbonate precipitation rate. G. fascicularis increased its respiration rate and expelled 71% of its symbiotic zooxanthellae algae under elevated pCO 2 . Photosynthetic pigments in the remaining zooxanthellae algae increased from 1.85 to 11.5 times to sustain its photosynthetic outputs. At the end of the experiment, G. fascicularis managed to increase the rate of its calcium carbonate precipitation. Increase pCO 2 in the atmosphere may affect species diversity of coral reefs.

pH homeostasis during coral calcification in a free ocean CO 2 enrichment (FOCE) experiment, Heron Island reef flat, Great Barrier Reef

“…Nonetheless, we find that the skeletal densities in the low pH FOCE corals differed by less than 3% from the densities of control corals (Table S3). Furthermore, the calcification rates that we measured were comparable to or higher than rates reported in prior studies (33,34), which further demonstrates the capacity of P. cylindrica from Heron Island reef flat to calcify and grow at normal rates despite the highly variable and disparate thermal and chemical conditions in the controls and in the FOCE treatments.…”

Preliminary results with a torsion microbalance indicate that carbon dioxide and exposed carbonic anhydrase in the organic matrix are the basis of calcification on the skeleton surface of living corals

“…Their own experiments indicated that, at normal temperatures, there was no response to elevated pCO 2 but when temperature and pCO 2 were both elevated, calcification dropped by 50%. Yii et al (2009) found an increase in calcification rate for Galaxea fascicularis and a decrease for Porites cylindrica with increased CO 2 levels. Muehllehner & Edmunds (2008) reported a small (+5%) increase in calcification rate at 29ºC for Porites rus (n=11) and a larger (+100%) increase for Pocillopora meandrina (n=9) with increased pCO 2 ; however at 27ºC there were reductions in calcification rate for both species.…”

Coral responses to temperature, irradiance and acidification stress: linking physiology to satellite remote sensing

“…Chlorophyll a per symbiont cell did not change under ocean acidification in the experimental study of P. acuta. However, in six out of seventeen exposures in the literature, ocean acidification caused statistically significant alterations in chlorophyll a per symbiont cell (Hii et al 2009;Crawley et al 2010;Krief et al 2010;Ogawa et al 2013;Horwitz and Fine 2014). In five out of six of these cases, chlorophyll a per symbiont cell increased ( Figure 4.2b).…”

“…pCO 2 partial pressure (in µatm) was not reported in Hii et al (2009), so consequently, this value had to be calculated from the reported CO 2 content of seawater in µmol•kg -1…”

“…For instance, under ocean acidification, Hii et al (2009) found declines in areal symbiont densities of 31% -70%, and Kaniewska et al (2012) found declines of 55%. These levels are akin to the levels seen during seasonal symbiont loss ("physiological bleaching") in corals (Fitt et al 2000), Due to its central role in coral photobiology, it is reasonable to suspect that light level may be involved in determining the impact of ocean acidification on Symbiodinium density and photobiology (Suggett et al 2013).…”