The effects of in situ shading on the growth of a seagrass, Syringodium isoetifolium

The effect of light reduction on a tropical seagrass, Syringodium isoetifolium, was examined over a period of six months (July 2001 to December 2001) in relation to leaf elongation rates, shoot densities and chlorophyll content of the leaf blades. The experiment was carried out at Poste Lafayette, Mauritius, in winter (July to September) and summer (October to December) in the same seagrass meadow. In both seasons three plots were shaded with Sarlon cloth (75% light cut-off), with three unshaded plots as controls. The growth rate for both winter and summer was higher in the shaded plots than in the control. Leaf elongation rates were higher in shaded plots in summer than in the shaded plots in winter. Blade chlorophyll was also higher in the shaded plots than in unshaded plots both in winter and in summer. There was no significant difference in the shoot density between plots. These results are consistent with the suggestion that high irradiance brings about a reduction in seagrass growth. The results also show that light is one of the factors that control the vertical growth response of S. isoetifolium as well as its photoreceptors.