Response of the temperate coral &amp;lt;i&amp;gt;Cladocora caespitosa&amp;lt;/i&amp;gt; to mid- and long-term exposure to &amp;lt;i&amp;gt;p&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; and temperature levels projected for the year 2100 AD

R Rodolfo-Metalpa,C Ferrier-Pagès,S Martin,J.-P Gattuso

doi:10.5194/bg-7-289-2010

Abstract

Abstract. Atmospheric CO2 partial pressure (pCO2) is expected to increase to 700 μatm or more by the end of the present century. Anthropogenic CO2 is absorbed by the oceans, leading to decreases in pH and the CaCO3 saturation state (Ω) of the seawater. Elevated pCO2 was shown to drastically decrease calcification rates in tropical zooxanthellate corals. Here we show, using the Mediterranean zooxanthellate coral Cladocora caespitosa, that an increase in pCO2, in the range predicted for 2100, does not reduce its calcification rate. Therefore, the conventional belief that calcification rates will be affected by ocean acidification may not be widespread in temperate corals. Seasonal change in temperature is the predominant factor controlling photosynthesis, respiration, calcification and symbiont density. An increase in pCO2, alone or in combination with elevated temperature, had no significant effect on photosynthesis, photosynthetic efficiency and calcification. The lack of sensitivity C. caespitosa to elevated pCO2 might be due to its slow growth rates, which seem to be more dependent on temperature than on the saturation state of calcium carbonate in the range projected for the end of the century.

Highlights

Atmospheric CO2 partial pressure has increased by 32% between 1880 and 2005 (280 vs. 379 μatm) and a further doubling is expected by the end of this century (IPCC, 2007)
The lack of sensitivity C. caespitosa to elevated pCO2 might be due to its slow growth rates, which seem to be more dependent on temperature than on the saturation state of calcium carbonate in the range projected for the end of the century
While temperature is a critical environmental parameter controlling the physiology and calcification of C. caespitosa, an increase in CO2 partial pressure, within the values expected by the end of 2100, did not significantly affect either their photosynthetic performance or the calcification rates

Summary

Introduction

Atmospheric CO2 partial pressure (pCO2) has increased by 32% between 1880 and 2005 (280 vs. 379 μatm) and a further doubling is expected by the end of this century (IPCC, 2007). Several studies on the effect of ocean acidification on fast-growing tropical corals show that calcification could decline by 0 to 56% under a doubling of pCO2 alone (Kleypas et al, 2006) or in combination with a +3 ◦C increase in temperature (Reynaud et al, 2003; Anthony et al, 2008). Anthony et al (2008) found that, in contrast to Acropora intermedia, Porites lobata exhibited a lower net productivity under intermediate CO2 concentrations (700 μatm), high temperature and irradiance regime. The only study that investigated the effect of high pCO2 on a Mediterranean coral, Oculina patagonica (Fine and Tchernov, 2007) revealed a complete dissolution of the skeleton at pH 7.4, a value lower than the one expected in 2100

Methods

Results

Conclusion