Macroalgae on Shallow Tropical Reefs Reduce the Availability of Reflected Light for Use in Coral Photosynthesis

• Autores: Nicholas B. Colvard, Peter J. Edmunds
• Localización: Bulletin of Marine Science, ISSN 0007-4977, Vol. 88, Nº. 4, 2012, págs. 1019-1033
• Idioma: inglés
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• Resumen

  • We tested the hypothesis that light reflected from dense growths of macroalgae [i.e., a low reflectance (LR) surface] vs heavily grazed surfaces [i.e., a high reflectance (HR) surface] has no effect on the photophysiology of scleractinian corals on the shallow (3-m depth) back reef of Moorea, French Polynesia. Underwater light was measured using a cosine-corrected sensor that detected photosynthetically active radiation (PAR, between 400 and 700 nm), and an underwater spectrophotometer that measured spectral reflectance, R([lambda]), with nanometer wavelength resolution. The effect of reflected light on corals was assessed by incubating small colonies of massive Porites spp. and Pocillopora verrucosa (Ellis and Solander, 1786) for 27 d on artificial HR and LR surfaces, and measuring the effective photochemical efficiency ([Delta]/Fm') of Symbiodinium on the sides of colonies adjacent to the benthos. At noon on a cloudless day, upwelling photon irradiance (Eu) from the benthos was reduced 20% over LR vs HR surfaces, and LR surfaces reduced R([lambda]) 50%-60% for PAR. For massive Porites spp., [Delta]F/Fm' did not differ between HR and LR surfaces, but for P. verrucosa, [Delta]F/Fm' increased 60% on LR compared to HR surfaces. The increase in [Delta]F/Fm' suggests that P. verrucosa modifies its photophysiological performance in tissue adjacent to LR surfaces to increase the efficiency with which light can be utilized in photochemical pathways.