Lateral light transfer ensures efficient resource distribution in symbiont-bearing corals

Abstract

Coral tissue optics has received very little attention in the past, although the interaction between tissue and light is central to our basic understanding of coral physiology. Here we used fibre-optic and electrochemical microsensors along with variable chlorophyll fluorescence imaging to directly measure lateral light propagation within living coral tissues. Our results show that corals can transfer light laterally within their tissues to a distance of ~2 cm. Such light transport stimulates O 2 evolution and photosystem II operating efficiency in areas >0.5-1 cm away from direct illumination. Light is scattered strongly in both coral tissue and skeleton, leading to photon trapping and lateral redistribution within the tissue. Lateral light transfer in coral tissue is a new mechanism by which light is redistributed over the coral colony and we argue that tissue optical properties are one of the key factors in explaining the high photosynthetic efficiency of corals.

Trophic dynamics of scleractinian corals: A stable isotope evidence

“…These measurements are in agreement with the observation that a high metabolic demand per cell usually impairs high symbiont concentration (Wooldridge, 2013). In turn, a smaller concentration in T. reniformis avoided self-shading and increased the amount of light reaching each symbiont, promoting photosynthesis (Wangpraseurt et al, 2014). Overall, host-symbiont differences can have induced large intrinsic metabolic differences between the two coral species (Gates and Edmunds, 1999), which might have affected energy fluxes within the symbiosis.…”

“…For example, T. reniformis presented lower growth rates as well as higher protein content and metabolic rates compared with S. pistillata, and might have exhibited higher protein turnover rates (Gates and Edmunds, 1999). A different light environment inside the host tissue (Wangpraseurt et al, 2012(Wangpraseurt et al, , 2014, clade-specific metabolic demands (Leal et al, 2015) or different growth rates might have led to differences in symbiont concentration. Significant genotypic differences were observed in the rates of nutrient acquisition, retention and translocation per cell (Table 1) between Symbiodinium of each coral species (Cantin et al, 2009;Baker et al, 2013).…”

Changes in the Number of Symbionts and Symbiodinium Cell Pigmentation Modulate Differentially Coral Light Absorption and Photosynthetic Performance

“…Micro-scale approaches are useful tools for the characterization of the internal light fields of the symbionts (Kühl et al, 1995;Wangpraseurt et al, 2012Wangpraseurt et al, , 2014Wangpraseurt et al, , 2016Brodersen et al, 2014). This approach has documented the presence of light gradients (Wangpraseurt et al, 2012) and lateral light transfer within coral tissues , which apparently are more pronounced in corals with thicker tissues.…”

Non-intrusive Assessment of Photosystem II and Photosystem I in Whole Coral Tissues

“…Such methods have been broadly applied to investigate light use efficiency (Gorbunov et al, 2001;Ralph et al, 2005;Szabó et al, 2014), photoacclimation (Hill and Ralph, 2005;Hennige et al, 2008;Lichtenberg et al, 2016), and photodamage (Ragni et al, 2010;Hill et al, 2011;Hill and Takahashi, 2014;Schrameyer et al, 2016) of intact corals under various environmental stress conditions. However, chlorophyll a fluorescence measurements of whole coral tissues are not always straightforward due to a strong light gradient and other complex optical properties specific to coral tissues (Enríquez et al, 2005;Wangpraseurt et al, 2012Wangpraseurt et al, , 2014Schrameyer et al, 2014;Lichtenberg et al, 2016). Light attenuation within coral tissue is strongly wavelength dependent (Wangpraseurt et al, 2012;Szabó et al, 2014), which particularly influences both the penetration depth of the excitation light beam projected onto the coral surface and the re-absorption of the fluorescence.…”