Abstract
Light spectrum plays a key role in the biology of symbiotic corals, with blue light resulting in higher coral growth, zooxanthellae density, chlorophyll a content and photosynthesis rates as compared to red light. However, it is still unclear whether these physiological processes are blue-enhanced or red-repressed. This study investigated the individual and combined effects of blue and red light on the health, zooxanthellae density, photophysiology and colouration of the scleractinian coral Stylophora pistillata over 6 weeks. Coral fragments were exposed to blue, red, and combined 50/50% blue red light, at two irradiance levels (128 and 256 μmol m−2 s−1). Light spectrum affected the health/survival, zooxanthellae density, and NDVI (a proxy for chlorophyll a content) of S. pistillata. Blue light resulted in highest survival rates, whereas red light resulted in low survival at 256 μmol m−2 s−1. Blue light also resulted in higher zooxanthellae densities compared to red light at 256 μmol m−2 s−1, and a higher NDVI compared to red and combined blue red light. Overall, our results suggest that red light negatively affects the health, survival, symbiont density and NDVI of S. pistillata, with a dominance of red over blue light for NDVI.
Highlights
Light plays a key role in the growth, reproduction and physiology of scleractinian corals that host phototrophic symbionts [1,2,3,4]
After week 3, corals grown under red and blue red light at an irradiance of 256 mmol m22 s21 started to show necrosis, which continued to progress towards mortality after week 4 and beyond
This study revealed distinct effects of light spectrum and irradiance on the health/survival, symbiont density, photophysiology and colouration of the scleractinian coral Stylophora pistillata
Summary
Light plays a key role in the growth, reproduction and physiology of scleractinian corals that host phototrophic symbionts [1,2,3,4]. Only few studies investigated the individual roles played by different colours within the visible light spectrum [5,6,7,8]. Blue light plays a key role in coral growth, colouration, and photophysiology, promoting coral and zooxanthellae growth, chlorophyll a content (either through increased zooxanthellae density or higher chlorophyll a per zooxanthella), fluorescent protein production, and increased photosynthesis rates [5,6,7,8]. The studies of Kinzie et al [5] and Wang et al [11] show that coral and zooxanthellae growth are blue-enhanced, it is still unclear whether red light acts neutrally on inhibitory on coral growth, zooxanthellae density, and photophysiology
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