Photosynthetic performance of the red alga Solieria pacifica (Solieriaceae) from two different depths in the sublittoral waters of Kagoshima, Japan

Abstract

Photosynthetic responses to photosynthetically active radiation (PAR) and temperature were examined in the red alga Solieria pacifica from deep (35 m) and shallow (5 m) portions of the sublittoral zone in Kagoshima, Japan. Dissolved oxygen sensors and pulse-amplitude modulated (PAM) fluorometry were used for the measurements of net photosynthesis, dark respiration rates, and photochemical efficiency. The photosynthetic performances of the deep- and shallow-water ecotypes provided substantial evidence of their adaptation to the ambient PAR and temperature conditions of their respective habitats. Both algal samples showed different temperature optima for photosynthesis: 19.5–19.9 °C for S. pacifica from Mageshima (MAG) and 18.6–27.0 °C for species from Yatsushiro Bay (YAT), that reflect the temperature ranges in the 35- and 5-m depths of the sublittoral zone, respectively. Maximum net photosynthetic rate (Pmax = 3.73 μg O2 gfw−1 min−1), compensation PAR (Ec = 21 μmol photons m−2 s−1), and saturation PAR (Ek = 131 μmol photons m−2 s−1) were higher in YAT S. pacifica than in MAG samples (Pmax = 1.55 μg O2 gfw−1 min−1, Ec = 3 μmol photons m−2 s−1, Ek = 15 μmol photons m−2 s−1), which can be attributed to the higher PAR levels experienced by the seaweeds occurring at depths of 5 m. The large depressions in effective quantum yields (ΦPSII) after chronic PAR exposures and failed recovery in maximum quantum yields (Fv/Fm) after dark acclimation of MAG S. pacifica suggest a greater tendency for photodamage in the deep-water ecotype. As for the shallow-water S. pacifica (YAT), complete recovery occurred only at 20 °C. Low temperature limitation may account for the decreased gross photosynthetic rates and delayed recovery of post-dark acclimation Fv/Fm of YAT S. pacifica at temperatures below their optimum, which can occur during winter.