The coral reef-dwelling Peneroplis spp. shows calcification resilience to ocean acidification conditions - results from culture experiments

<p>Ocean acidification is a consequence of current anthropogenic climate changes.&#160;The concomitant decrease in pH and carbonate ion concentration in sea water may have severe impacts on calcifying organisms. Coral reefs are among the first ecosystems recognized vulnerable to ocean acidification. Within&#160;coral reefs, large benthic foraminifera (LBF) are major calcium carbonate producers.</p><p>The aim of this study was to evaluate the effects of varying&#160;pH on&#160;survival and calcification of the&#160;symbiont-bearing LBF species <em>Peneroplis</em> spp.&#160;We performed culture experiments to study their&#160;resistance to ocean acidification conditions,&#160;as well as their resilience once placed back under open ocean pH (7.9).</p><p>After three&#160;days, small signs of test decalcification were observed on specimens kept at pH 7.4, and severe test decalcification was observed on specimens kept at pH 6.9, with the inner organic lining clearly appearing.&#160;After 32 days under pH 7.4, similar strongly decalcified specimens were observed. All the specimens were alive&#160;at the end of the experiment. This result demonstrates the&#160;resistance of <em>Peneroplis </em>spp.&#160;to an acidified pH, at least on a short period of time.</p><p>After being partially decalcified, some of the living specimens were placed back at pH 7.9. After one month, the majority of the specimens showed recalcification&#160;features, mostly by addition of new chambers.&#160;The trace elements concentrations of the newly formed chambers were analysed by LA-ICPMS. Interestingly, more chambers were added when food was given, which&#160;highlights the crucial role of energy source in the&#160;recalcification process. Moreover, the newly formed chambers were most of the time abnormal, and the general structure&#160;of the tests was altered, with potential impacts on reproduction and in situ survival. In conclusion, if symbiont-bearing LBF show some resistance and resilience to&#160;lowered pH&#160;conditions, they&#160;will remain&#160;strongly affected by ocean acidification.</p>