Physiological studies of subtidal red algae

Abstract

The net photosynthesis of the subtidal red algae Euthora cristata (C. Agardh) J. Agardh, Phycodrys rubens (L. ) Batters, Phyllophora truncata (Pallas) Newroth et Taylor and Ptilota serrata Kützing were determined under a variety of different light and temperature regimes. The optimal light requirements for net photosynthesis of the species are relatively low, mostly ranging from 465 to 747 ft-c at 5 ° and 15 °C. Seasonal and spatial differences were found in the photosynthesis-light responses of Phyllophora truncata and Ptilota serrata; winter plants exhibited lower light optima for net photosynthesis than spring plants. Deep-water populations of Ptilota showed lower light optima and reduced net photosynthesis as compared with shallow subtidal populations. Summer plants of Euthora cristata, Phycodrys rubens and Phyllophora truncata showed a greater tolerance to high temperatures and higher temperature optima than winter plants. It is suggested that optimal temperature and light requirements of seaweeds are adjusted in an adaptive fashion to the environmental regimes of their habitats. The temperature requirements of the four species are discussed in relation to their local estuarine distributions in New England; eurythermal species have the widest estuarine distributions. Cystocarpic and tetrasporic plants of Euthora cristata and Ptilota serrata show differential physiological responses and vertical distributions. The significance of higher rates of net photosynthesis and lower light optima are discussed in relation to vertical stratification of different generations.