Light Respiratory Processes and Gross Photosynthesis in Two Scleractinian Corals

<div><p>The light dependency of respiratory activity of two scleractinian corals was examined using O₂ microsensors and CO₂ exchange measurements. Light respiration increased strongly but asymptotically with elevated irradiance in both species. Light respiration in <i>Pocillopora damicornis</i> was higher than in <i>Pavona decussata</i> under low irradiance, indicating species-specific differences in light-dependent metabolic processes. Overall, the coral <i>P. decussata</i> exhibited higher CO₂ uptake rates than <i>P. damicornis</i> over the experimental irradiance range. <i>P. decussata</i> also harboured twice as many algal symbionts and higher total protein biomass compared to <i>P. damicornis</i>, possibly resulting in self-shading of the symbionts and/or changes in host tissue specific light distribution. Differences in light respiration and CO₂ availability could be due to host-specific characteristics that modulate the symbiont microenvironment, its photosynthesis, and hence the overall performance of the coral holobiont.</p>