Conceptual model of light and carbon availability, in the two hard coral species, <i>Pocillopora damicornis</i> and <i>Pavona decussata</i> in moderate light (∼100 µmol photons m⁻² s⁻¹).

<p>The schematic diagram of a coral shows the coral tissue containing algal symbionts (green circles), which lies above the calicoblastic layer. Photosynthetic active radiation (PAR) (rainbow arrow) penetrates the coral tissue. In <i>P. decussata</i> a higher density of symbionts reduced light availability compared to <i>P. damicornis</i>. Dissolved inorganic carbon (grey arrows; quantity is relative to arrow thickness) can originate from internal sources such as the calicoblastic layer or from the external environment, where <i>P. decussata</i> draws stronger on the external carbon uptake. Light respiration (R) (strength indicated through size), was greater in <i>P. damicornis</i> than in <i>P. decussata</i>.