Calcification responses of symbiotic and aposymbiotic corals to near-future levels of ocean acidification

Abstract

Abstract. Increasing the acidity of ocean waters will directly threaten calcifying marine organisms such as reef-building scleractinian corals, and the myriad of species that rely on corals for protection and sustenance. Ocean pH has already decreased by around 0.1 pH units since the beginning of the industrial revolution, and is expected to decrease by another 0.2–0.4 pH units by 2100. This study mimicked the pre-industrial, present, and near-future levels of pCO2 using a precise control system (± 5% pCO2), to assess the impact of ocean acidification on the calcification of recently settled primary polyps of Acropora digitifera, both with and without symbionts, and adult fragments with symbionts. The increase in pCO2 of ~100 μatm between the pre-industrial period and the present had more effect on the calcification rate of adult A. digitifera than the anticipated future increases of several hundreds of micro-atmospheres of pCO2. The primary polyps with symbionts showed higher calcification rates than primary polyps without symbionts, suggesting that: (i) primary polyps housing symbionts are more tolerant to near-future ocean acidification than organisms without symbionts, and (ii) corals acquiring symbionts from the environment (i.e., broadcasting species) will be more vulnerable to ocean acidification than corals that maternally acquire symbionts.

Effects of acidified seawater on calcification, photosynthetic efficiencies and the recovery processes from strong light exposure in the coral Stylophora pistillata

“…Similarly, Ohki et al. () reported that photosynthetic efficiencies of Acropora digitifera were not affected by acidified seawater (pH 7.7–8.1), and the same pattern was also reported in Acropora cervicornis in the Caribbean (Enochs et al., ). Conversely, a decrease in Fv/Fm was observed in acidified seawater (pH 7.4–8.0) in the massive coral Porites australiensis in acidified seawater (Iguchi et al., ).…”

The role of symbiotic algae in the formation of the coral polyp skeleton: 3-D morphological study based on X-ray microcomputed tomography

“…[] and Ohki et al . []. In these culture experiments, 40–60 primary polyps were cultured in each experimental condition.…”

“…[] and Ohki et al . []. Symbiotic and aposymbiotic primary polyps were cultured for 10 days in each experiment.…”

An aposymbiotic primary coral polyp counteracts acidification by active pH regulation

“…1c,c: black arrow). Because the skeletal growth of aposymbiotic primary polyps of A. digitifera is very sensitive to exposure to acidified seawater18, this system is convenient for observing changes in pH SCM after exposure to acidified seawater. Calcification occurs at the interface between the tissue and the glass substrate16.…”

“…Our system allowed the visualization of the coral primary polyp SCM (Fig. 1d: red dotted line) which could estimate pH SCM without the effects of photosynthesis and respiration by symbiotic algae1819.…”