Catalogus

Leaf spectral transmittance [T_L(λ)], reflectance [R_L(λ)], and non-photosynthetic absorptance [A_L(NP)] were measured in order to calculate leaf spectral absorptance [A_L(λ)] and photosynthetic leaf absorptance [A_L(PAR)]. Leaf spectra for the seagrasses were similar in shape, but variable in magnitude. Greatest among-species differences in leaf optical properties were present across green (500–600 nm) and near infrared (700–750 nm) wavelengths. This suggests differences in seagrass leaf optical properties are mainly due to variations in accessory pigments and leaf functional anatomy (e.g., internal structure, sclerenchyma fibers, etc.). Reflectance of photosynthetically active radiation (PAR) by leaves [%R_L(PAR)] ranged from 4.6 to 9.3% with a mean of 6.1 ± 1.2%. A_L(NP) was more variable (16 ± 5%) than %R_L(PAR) among species and sites. P. coriacea, a seagrass characteristic of high energy environments with the most structurally reinforced leaves, had the highest values of %R_L(PAR) (9.3 ± 1.4%) and A_L(NP) (29 ± 8%). A_L(PAR) values ranged from 45 ± 3% for H. ovalis from a shallow (1 m) open coastal site in Western Australia to 68 ± 3% for P. australis from a deeper (3 m) protected site in New South Wales. The overall mean A_L(PAR) of 57 ± 6% for the seagrasses measured here is over 30% lower than the absorption factor of 84%, commonly used in PAM fluorometric studies of seagrasses. Because of the relatively low within-species variability in this parameter, A_L(PAR) was significantly higher for the eight large-bodied species (59 ± 6%) compared to the small-bodied H. ovalis (53 ± 5%). This limited survey of seagrass leaf optical characteristics indicates relatively low variability in light absorption across a wide range of leaf morphologies and environments consistent with previous suggestions of constraints on light absorption by aquatic plants.