Emergent Properties Of Branching Morphologies Modulate The Sensitivity Of Coral Calcification To High P-co2

Experiments with coral fragments (i.e. nubbins) have shown that net calcification is depressed by elevated P-CO2. Evaluating the implications of this finding requires scaling of results from nubbins to colonies, yet the experiments to codify this process have not been carried out. Building from our previous research demonstrating that net calcification of Pocillopora verrucosa (2-13 cm diameter) was unaffected by P-CO2 (400 and 1000 mu atm) and temperature (26.5 and 29.7 degrees C), we sought generality to this outcome by testing how colony size modulates P-CO2 and temperature sensitivity in a branching acroporid. Together, these taxa represent two of the dominant lineages of branching corals on Indo-Pacific coral reefs. Two trials conducted over 2 years tested the hypothesis that the seasonal range in seawater temperature (26.5 and 29.2 degrees C) and a future P-CO2 (1062 mu atm versus an ambient level of 461 mu atm) affect net calcification of an ecologically relevant size range (5-20 cm diameter) of colonies of Acropora hyacinthus. As for P. verrucosa, the effects of temperature and P-CO2 on net calcification (mg day(-1)) of A. verrucosa were not statistically detectable. These results support the generality of a null outcome on net calcification of exposing intact colonies of branching corals to environmental conditions contrasting seasonal variation in temperature and predicted future variation in P-CO2. While there is a need to expand beyond an experimental culture relying on coral nubbins as tractable replicates, rigorously responding to this need poses substantial ethical and logistical challenges.