Efficient light‐harvesting of mesophotic corals is facilitated by coral optical traits

Abstract

Scleractinian corals are the primary building blocks of coral reef ecosystems. The underlying success of corals as ecosystem engineers is mainly due to the complex interaction that takes place between the coral hosts and their endosymbiont microalgae (family: Symbiodiniaceae). The coral-algal symbiosis is driven by solar energy and acts as the biological engine fuelling the reef (Roth, 2014). Corals have adapted to capture and maximize light under various environmental conditions, and it has been suggested that they are among the most efficient photosynthetic organisms at utilizing and convert-

Morpho-functional traits of the coral Stylophora pistillata enhance light capture for photosynthesis at mesophotic depths

“…Overall, samples from shallow depths exhibited a more rapid attenuation of light in the tissue and a greater ability to cope with excess light under high intensities, given that above the tissue surface the escaping flux (Φ) was enhanced by up to twofold higher from the incident irradiance (Fig. 5 ), thus supporting previous ecophysiological observations of light-adapted photosynthetic performance 31 , 33 . On the colony scale, Hoogenboom et al 41 found evidence of a strong reduction in energy available for coral growth under high-light levels and suggested that corals avoid the costs of excessive light exposure by means of altering colony morphology.…”

“…Based on the results of the morphometric analyses and the optical data from Kramer et al (2022 31 ; Tables S1-3 ), we performed a total of 112 optical simulations (Figs. 5 and 6 ; Figs.…”

“…However, understanding how the different mechanisms of photoadaptation (e.g., morphological, physiological, and optical) interact to influence photosynthesis under a specific light regime is critical in determining the photic boundaries of any particular coral species. Integrating our morphometric results with recently obtained photosynthetic and optical data 31 , and using three-dimensional light propagation models, we applied a novel method by which to determine the functional significance of small-scale morphological traits with respect to the coral's internal irradiance distribution.…”

“…The greater space occupied by the coenosteum relative to the corallites, as documented for mesophotic-depth colonies, may reflect the host’s response to minimize light limitation for its photosymbionts. This response may reduce the denser pigmentation of the polyps, as the polyps reveal the largest pigmentation cross-section when all the tentacles are retracted 31 , 48 .…”

“…1 and Table S1 ). For the coral tissue, we assumed thicknesses based on previous measurements 31 . We acknowledge that under natural conditions coral tissues are flexible, and expansion and contraction can affect light propagation.…”