Photosynthetic responses of Florida seaweeds to light and temperature: a physiological survey

The photosynthetic responses of 37 tropical seaweeds (14 Chlorophyceae, 5 Phaeophyceae and 18 Rhodophyceae) were measured in a Gilson Warburg Apparatus under a variety of light and temperature regimes. The brown algae Padina vickersiae and Sporochnus pedunculatus exhibited the lowest saturation light intensity (263 μE/m²/sec), while five green algae (Acetabularia crenulata, Cladophora coelothrix, Dictyosphaeria cavernosa, Monostroma oxyspermum and Codium repens) had the highest light optima (3,843–4,258 μE/m²/sec). Overall, the Chlorophyceae exhibited the broadest range of light optima; in contrast, the Phaeophyceae primarily had low light optima, while several Rhodophyceae had higher light optima. The thermal optima for 34 seaweeds ranged from 15–30°C. Catoglossa leprierii, Botryocladia occidentalis, Codium taylorii, Soliera tenera and Codium intertextum exhibited relatively broad thermal optima, with C. leprierii having the most eurythermal response. The Chlorophyceae exhibited thermal optima between 15–30°C, the Phaeophyceae between 15–27°C, and most Rhodophyceae between 18–24°C. Few taxa, except for Cladophora coelothrix and Dictyosphaeria cavernosa, had broad physiological tolerances to both high temperature and light regimes. Overall, the Phaeophyceae exhibited the most restricted temperature and light optima, while the Chlorophyceae and Rhodophyceae exhibited broader tolerances.