Abstract
ABSTRACTCoral reefs are essential to many nations, and are currently in global decline. Although climate models predict decreases in seawater pH (∼0.3 units) and oxygen saturation (∼5 percentage points), these are exceeded by the current daily pH and oxygen fluctuations on many reefs (pH 7.8–8.7 and 27–241% O2 saturation). We investigated the effect of oxygen and pH fluctuations on coral calcification in the laboratory using the model species Acropora millepora. Light calcification rates were greatly enhanced (+178%) by increased seawater pH, but only at normoxia; hyperoxia completely negated this positive effect. Dark calcification rates were significantly inhibited (51–75%) at hypoxia, whereas pH had no effect. Our preliminary results suggest that within the current oxygen and pH range, oxygen has substantial control over coral growth, whereas the role of pH is limited. This has implications for reef formation in this era of rapid climate change, which is accompanied by a decrease in seawater oxygen saturation owing to higher water temperatures and coastal eutrophication.
Highlights
Coral reefs provide essential goods and ecosystem services to many nations worldwide (Moberg and Folke, 1999)
Light calcification rates of the scleractinian coral Acropora millepora were variable between treatments and ranged from 0.1160.02 to 0.3060.01 mg CaCO3 g coral21 h21 (Fig. 1)
The results clearly show the profound effects of seawater oxygen saturation on light and dark calcification rates of A. millepora, whereas the role of pH in our experiments was limited to light conditions
Summary
Coral reefs provide essential goods and ecosystem services to many nations worldwide (Moberg and Folke, 1999). The projected pH decrease for this century is greatly exceeded by the daily pH fluctuation to which Indo-Pacific corals on reef flats and lagoons are exposed, which ranges from 8.7 during the day to 7.8 at night (Ohde and van Woesik, 1999). Received 10 February 2014; Accepted 22 April 2014 reef locales shows dramatic changes over a diel cycle, with a range of 241% air saturation (or 14.19 mg O2 L21) at daytime, to 27% saturation (or 1.67 mg O2 L21) at night (Ohde and van Woesik, 1999)
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