SUBMERGED LIFE. “The photosynthetic apparatus needs to be modulated to accommodate the changes in light attenuation through the water depth. Consequently, the overall light intensity is decreased and the wavelength composition of sunlight reaching underwater plants is different. Accordingly, seagrasses have one of the highest light requirements among angiosperms.”
http://bmcevolbiol.biomedcentral.com/articles/10.1186/1471-2148-11-8