Abstract:The chlorophyll fluorescence of the blades of three common seagrass species (Zostera marina, Z. caespitosa and Phyllospadix iwatensis) in eastern waters of Chudao, south coast of Sanggou Bay, was determined using the pulse amplitude modulated (PAM) fluorometer. The absorbance factor (AF) of seagrass blades were also determined,and the absolute electron transport rates of the seagrass species were calculated.It was found that the photosynthetic activity of Z. marina, Z. caespitosa and P. iwatensis, was strongly influenced by leaf age. The chlorophyll content and the AF values increased with blade age in respective plants. Young blades showed higher electron transport rate than older ones (Zm: Leaf 1=26.56, Leaf 2=16.3, Leaf 3= 19.98; Pi: Leaf 1 =22.31, Leaf 2=19.23, Leaf 3=17.06; and Zc: Leaf 1=20.16, Leaf 2 =16.10，Leaf 3=13.10). Among three species, Z. marina showed the highest photosynthetic activity (ETRmax=22.67), in accordance with its highest productivity in the field compared with the other two species.
